−---
−title: HVAC Ductwork
−category: Mechanical / Air Distribution
−toc_depth: 3
−description: >
− When to use: Metal and flexible ductwork for low-pressure, medium-pressure, and high-pressure HVAC air distribution systems in commercial, institutional, and industrial buildings. Covers rectangular, round, flat-oval, and flexible duct; pressure and seal classifications; gauge and reinforcement; fittings and turning vanes; duct liner and external insulation; sealants; fire and smoke dampers; access doors; hangers and supports; leakage testing; and field verification. Applies to new construction and major renovation of supply, return, exhaust, and outside-air distribution systems.
− Not intended for: Kitchen exhaust grease duct systems (see [[sync/kitchen-exhaust-systems]]); industrial process ventilation conveying particulates, corrosive gases, or high-temperature products; fume hood exhaust systems; pneumatic tube systems; chilled-water or hydronic piping insulation (see [[sync/building-thermal-insulation]]); air-handling unit casing and coil sections (see [[sync/air-handling-units]]); air terminal units (see [[sync/air-terminal-units]]); air distribution devices at duct outlets (see [[sync/hvac-air-distribution-devices]]); testing, adjusting, and balancing of the completed air distribution system (see [[sync/testing-adjusting-and-balancing]]).
−---
−
−# Scope
−
−This standard covers the materials, fabrication, installation, sealing, insulation, support, testing, and field verification of HVAC ductwork systems for commercial and institutional buildings. All duct construction shall conform to ANSI/SMACNA 006-2020, HVAC Duct Construction Standards — Metal and Flexible, Fourth Edition, and shall satisfy the requirements of the adopted edition of the International Mechanical Code (IMC), NFPA 90A, and ASHRAE 90.1 for the jurisdiction of the project. Where these references conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
−
−Ductwork is the backbone of every air distribution system. Undersized or leaky ductwork wastes fan energy, fails to deliver design airflow, causes noise and vibration, and creates thermal comfort complaints that are difficult and expensive to correct after construction. Over-specified ductwork adds unnecessary cost and weight. This standard is written to establish a clear, consistent baseline that delivers the design pressure class, the design leakage class, and the design insulation performance — nothing less, nothing more — with the quality controls and testing needed to verify that the installed system performs as intended.
−
−Coordinate the duct system with the air-handling unit connections specified in [[sync/air-handling-units]], with air terminal unit connections in [[sync/air-terminal-units]], and with the outlet and inlet devices in [[sync/hvac-air-distribution-devices]]. Coordinate leakage testing, flow measurement, and air-balancing activities with [[sync/testing-adjusting-and-balancing]]. Coordinate thermal insulation of ducts outside the building with [[sync/building-thermal-insulation]] where project-specific requirements supplement this standard.
−
−# Referenced Standards
−
−Equipment, materials, and installation shall comply with the latest editions of the following standards adopted by the project jurisdiction. Where a specific edition is referenced in contract documents or by the local building code, that edition shall govern.
−
−| Standard | Title |
−|----------|-------|
−| ANSI/SMACNA 006-2020 | HVAC Duct Construction Standards — Metal and Flexible, Fourth Edition |
−| ANSI/SMACNA 016-2012 | HVAC Air Duct Leakage Test Manual, Second Edition |
−| ASHRAE 90.1 | Energy Standard for Buildings Except Low-Rise Residential Buildings (current adopted edition) |
−| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems (current adopted edition) |
−| IMC | International Mechanical Code (current adopted edition) |
−| UL 181 | Standard for Factory-Made Air Ducts and Air Connectors |
−| UL 181A | Standard for Closure Systems for Use with Rigid Air Ducts |
−| UL 181B | Standard for Closure Systems for Use with Flexible Air Ducts and Air Connectors |
−| UL 555 | Standard for Fire Dampers |
−| UL 555S | Standard for Smoke Dampers |
−| ASTM A653 | Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated by the Hot-Dip Process |
−| ASTM B209 | Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate |
−| ASTM A240 | Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and General Applications |
−| ASTM C1071 | Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material) |
−| ASTM C553 | Standard Specification for Mineral Fiber Blanket Thermal Insulation for Commercial and Industrial Applications |
−| ASTM E84 | Standard Test Method for Surface Burning Characteristics of Building Materials |
−| NFPA 90B | Standard for the Installation of Warm Air Heating and Air-Conditioning Systems |
−
−# Submittals
−
−## Action Submittals
−
−The Contractor shall submit the following for the Engineer's review and return prior to procurement or installation of the corresponding duct system components. No fabrication or installation shall proceed on a duct system or duct component until the associated submittal has been reviewed and returned with no outstanding engineering questions.
−
−- Product data for each duct material, including the metal specification, coating designation, and gauge schedules proposed for each pressure class
−- Product data for duct sealants, tapes, and mastics, including the applicable UL 181, UL 181A, or UL 181B listing, the manufacturer's cure and surface preparation requirements, and the working temperature range
−- Product data and cut sheets for flexible duct, including the UL 181 listing, the insulation R-value, the vapor jacket material, and the maximum recommended bend radius
−- Product data for fire dampers and smoke dampers, including UL 555 and UL 555S listings, the pressure class, the blade orientation, the actuator type, and the access requirements
−- Product data for duct liner and external duct wrap insulation, including ASTM C1071 conformance for liner, the R-value, the facing material, and the flame-spread and smoke-developed indices
−- Leakage test plan, prepared before testing begins, identifying the duct sections to be tested, the test pressures, the instruments to be used, and the acceptance criteria
−- Shop drawings showing duct routing, offset dimensions, fitting configurations, hanger locations, access door locations, and the coordination of duct penetrations with fire-rated assemblies where the routing deviates from the contract drawings
−
−```datasheet
−label: Action Submittals Required
−type: checkbox
−options:
− - "Product data — duct materials (metal specification, gauge, coating)"
− - "Product data — duct sealants, mastics, and tapes"
− - "Product data — flexible duct (UL 181 listing, R-value)"
− - "Product data — fire and smoke dampers"
− - "Product data — duct liner and external insulation"
− - "Leakage test plan"
− - "Shop drawings for duct routing and coordination"
−default: "Product data — duct materials (metal specification, gauge, coating)"
−```
−
−## Closeout Submittals
−
−At substantial completion and before final acceptance of the duct system, the Contractor shall provide:
−
−- Leakage test reports for all tested duct sections, signed by the testing technician, documenting the test method, instruments (with calibration dates), ambient conditions, measured leakage rates, acceptance criteria, and pass/fail determination; include the corrective action taken and re-test results for any failed section
−- Damper schedule as-built, listing each fire damper and smoke damper by tag number, the fire-rated assembly it serves, the UL listing number, and the access door location
−- Operation and maintenance data for fire dampers, smoke dampers, and motorized control dampers, including manufacturer maintenance intervals and actuator replacement procedures
−- Warranty documentation for ductwork components carrying a manufacturer warranty
−
−# Quality Assurance
−
−## Installer Qualifications
−
−Duct fabrication and installation shall be performed by a sheet-metal contractor whose work force consists of trained sheet-metal workers. Fabrication of spiral wound and longitudinal seam round duct, flat-oval duct, and rectangular duct shall be performed by personnel experienced in the pressure class and seal class specified. Personnel responsible for fire-damper installation shall have received training from the damper manufacturer or a distributor for the specific damper series being installed.
−
−## Regulatory Inspection and Coordination
−
−The Contractor shall coordinate the scheduling of inspections of fire damper installations, duct penetrations of rated barriers, and duct liner installations with the Authority Having Jurisdiction before those elements are concealed. Fire dampers installed in rated barriers shall not be concealed by ceiling finishes, furring, or access panels until the damper installation has been inspected and released. The Contractor shall submit the damper schedule to the AHJ with sufficient lead time to schedule the inspection without delaying construction.
−
−## Source Quality Control
−
−Duct materials shall be purchased from suppliers who provide mill certifications confirming conformance to the applicable ASTM material specification. Certifications shall be retained by the Contractor for the duration of the project and made available to the Engineer on request. Gauge shall not be reduced below the SMACNA HVAC Duct Construction Standards minimum for the declared pressure class under any circumstances, including bid-phase value engineering, without a written change order.
−
−## Mock-Up
−
−Where the project involves more than 5,000 ft² of duct cross-sectional area at a single pressure class, or where the Engineer specifies it, the Contractor shall install a mock-up panel of the specified seal class before beginning production work. The mock-up shall be of a size sufficient to demonstrate the joint type and sealant application proposed. The Engineer shall review the mock-up for conformance with the seal class requirements of this standard before authorizing production installation.
−
−# Environmental and Service Conditions
−
−Ductwork must be designed and fabricated for the environmental conditions of its installed location. Metal ductwork in contact with dissimilar metals, in corrosive environments, or exposed to outdoor weather requires material selection and protective measures beyond the standard galvanized steel used in normal interior applications.
−
−## Interior Conditioned or Mechanical Space
−
−Standard galvanized steel conforming to ASTM A653, G90 coating designation, is appropriate for normal interior HVAC applications in conditioned or semiconditioned spaces. G90 provides a minimum average total-both-sides coating of 0.90 oz/ft² and gives adequate corrosion life in normal building environments.
−
−## Exterior and Outdoor-Air Applications
−
−Duct installed outdoors, in partially open parking structures, in outdoor air plenums, or in other locations exposed to weather, driving rain, or sustained high humidity shall use a heavier galvanized coating, aluminum alloy, or stainless steel as specified by the Engineer. External insulation and jacketing applied over outdoor duct shall protect the metal from moisture intrusion.
−
−## Corrosive and High-Humidity Applications
−
−In indoor swimming pools, natatoriums, chemical storage areas, and other spaces with corrosive or persistently high-humidity conditions, duct material selection shall be approved by the Engineer for the specific environment. Standard galvanized steel is not acceptable where chloride concentrations, pool chemical vapors, or persistent condensation would attack the zinc coating.
−
−```datasheet
−label: Duct Material for this System
−type: radio
−options:
− - "Galvanized steel, ASTM A653, G90 coating (standard interior)"
− - "Galvanized steel, ASTM A653, G90 coating, with exterior insulation jacket"
− - "Aluminum alloy, ASTM B209, 3003-H14 or 5052-H32"
− - "Stainless steel, ASTM A240, Type 304"
− - "Stainless steel, ASTM A240, Type 316 (corrosive environments)"
−default: "Galvanized steel, ASTM A653, G90 coating (standard interior)"
−```
−
−Aluminum ductwork offers significant weight reduction compared to galvanized steel and natural corrosion resistance, making it appropriate for outdoor applications and some corrosive environments. Aluminum shall not be installed in contact with dissimilar metals, cementitious materials, or soil without isolating gaskets or coatings because galvanic attack will rapidly consume the aluminum. Stainless steel type 304 provides resistance to general corrosion; type 316 shall be used where chloride exposure is anticipated, because chlorides attack the passive film on type 304 and cause pitting.
−
−# Duct Materials
−
−## Galvanized Steel
−
−Galvanized steel duct shall conform to ASTM A653, structural quality, with a hot-dip G90 zinc coating. The steel shall be of lock-forming quality, capable of fabrication into duct with seams, joints, and reinforcement attachments without cracking or delamination of the zinc coating. G90 coating corresponds to a minimum average zinc deposit of 0.90 oz/ft² total-both-sides. G60 coating shall not be substituted for G90 in ductwork.
−
−Gauge (minimum sheet thickness) for galvanized steel duct shall conform to ANSI/SMACNA 006-2020 for the declared pressure class. The 4th Edition of SMACNA standardized on minimum (not nominal) sheet thickness; the Contractor shall verify that the steel purchased meets the minimum thickness specified by SMACNA for each pressure class and duct size, not merely the nominal gauge designation, because nominal gauge thicknesses vary by supplier and may not satisfy the SMACNA minimum. Representative gauge ranges by pressure class are shown in the datasheet element below; the actual SMACNA tables govern.
−
−```datasheet
−label: Rectangular Duct Gauge Schedule
−type: radio
−options:
− - "Per SMACNA Table 1-3 for pressure class declared — minimum thickness governs"
− - "Heavier gauge specified by Engineer — see drawings"
−default: "Per SMACNA Table 1-3 for pressure class declared — minimum thickness governs"
−```
−
−For rectangular duct, typical galvanized gauge requirements for 2″ w.g. pressure class range from 26 gauge (0.016 in. minimum) for duct up to approximately 30 in. wide to 18 gauge (0.052 in. minimum) for the largest duct sizes, with intermediate gauges for intermediate widths, before accounting for intermediate or major reinforcement. For 4″ w.g. pressure class, gauges are heavier throughout. The Contractor shall use the SMACNA tables for the declared pressure class and shall not reduce gauge by more than one step based on a reinforcement upgrade without verifying that the alternate construction satisfies the SMACNA equivalent construction provisions.
−
−## Aluminum
−
−Aluminum duct sheet and strip shall conform to ASTM B209, alloy 3003-H14 or 5052-H32. Aluminum gauge schedules for the pressure class shall be selected from the SMACNA HVAC Duct Construction Standards tables applicable to aluminum. Because aluminum has a lower modulus of elasticity than steel, gauge and reinforcement requirements differ from those for galvanized steel at the same pressure class; the SMACNA aluminum tables shall be used rather than substituting equivalent steel gauges.
−
−All aluminum fittings, flanges, reinforcement angles, and attachment hardware in contact with aluminum duct shall be aluminum or stainless steel. Steel fasteners shall not be used in aluminum duct assemblies in corrosive or wet environments because the resulting galvanic cell consumes the aluminum. Where aluminum duct connects to steel equipment, an isolating transition coupling or gasket shall be provided.
−
−## Stainless Steel
−
−Stainless steel duct sheet shall conform to ASTM A240. Type 304 is appropriate for most applications where stainless is required. Type 316 shall be used where chloride contamination is anticipated. Gauge schedules shall conform to SMACNA or shall be calculated by the Engineer for the declared pressure class; stainless steel has higher yield strength than galvanized steel at equivalent gauge, so SMACNA stainless tables reflect reduced gauge requirements relative to steel. Welding, if required for stainless steel ductwork, shall be performed by qualified welders using stainless filler metal compatible with the base alloy.
−
−# Pressure and Seal Classifications
−
−## Pressure Classes
−
−Duct pressure class designates the maximum static pressure the duct must withstand and governs gauge, reinforcement, seam type, and seal class selection. SMACNA defines pressure classes of ±0.5, ±1, ±2, ±3, ±4, ±6, and ±10 in. w.g. The pressure class shall be established by the mechanical engineer based on the system fan static pressure, the duct routing, and the pressure distribution in the system, and shall be indicated on the contract documents for each duct system or duct zone.
−
−Where the pressure class is not indicated on the contract documents, the Contractor shall use +1 in. w.g. for low-pressure supply and return systems in accordance with SMACNA. Variable-air-volume systems with pressure-independent boxes shall use the pressure class corresponding to the maximum static pressure at the inlet to each duct zone, not the average system pressure.
−
−```datasheet
−label: Duct Pressure Class
−type: select
−unit: in. w.g.
−drawing_ref: true
−options:
− - "±0.5 in. w.g."
− - "±1 in. w.g."
− - "±2 in. w.g."
− - "±3 in. w.g."
− - "±4 in. w.g."
− - "±6 in. w.g."
− - "±10 in. w.g."
−default: "±1 in. w.g."
−```
−
−A common design error is specifying +1 in. w.g. pressure class throughout a medium-pressure VAV system and relying on SMACNA's "if not stated, use 1 in." default. The 1 in. w.g. pressure class is only appropriate at duct points where the actual static pressure is 1 in. w.g. or less. Where the duct is directly connected to a fan outlet or immediately downstream of a VAV fan that operates at 3–5 in. w.g. total static, the duct immediately adjacent to the fan must be designed for the higher pressure class. The Engineer shall designate pressure zones and indicate the applicable pressure class for each zone on the mechanical drawings.
−
−## Seal Classes
−
−Seal classes govern which duct surfaces must be sealed and the application method. SMACNA defines three seal classes, with Class A being the most stringent and Class C the least:
−
−**Seal Class A** — All transverse joints, all longitudinal seams, and all duct wall penetrations (including wire and control penetrations) shall be sealed. Required for pressure class 4 in. w.g. and above. Where indicated on the contract documents, Class A may also be required at lower pressure classes for energy-efficiency or clean-room projects.
−
−**Seal Class B** — All transverse joints and all longitudinal seams shall be sealed. Penetrations through the duct wall are not required to be sealed under Seal Class B alone, but penetrations shall be sealed where the system energy standard requires it. Required for pressure class 3 in. w.g.
−
−**Seal Class C** — Transverse joints only shall be sealed. Permitted for pressure class 2 in. w.g. and below. Many energy codes and project-specific requirements mandate Seal Class B or higher even at low pressure classes; the Contractor shall apply the more stringent requirement.
−
−```datasheet
−label: Duct Seal Class
−type: radio
−options:
− - "Class A — all transverse joints, longitudinal seams, and wall penetrations"
− - "Class B — all transverse joints and longitudinal seams"
− - "Class C — transverse joints only"
−default: "Class B — all transverse joints and longitudinal seams"
−```
−
−ASHRAE 90.1 requires that supply and return air ducts in unconditioned spaces, and all ducts in high-pressure systems, be sealed to the level required for the declared pressure class. Many jurisdictions adopting ASHRAE 90.1 or IECC effectively mandate Seal Class B for all commercial duct systems regardless of pressure class. The Engineer shall confirm the energy code requirement for the project jurisdiction and designate the minimum seal class accordingly on the contract documents. Specifying Seal Class B as the project default regardless of pressure class is the conservative and increasingly standard practice for commercial work.
−
−# Duct Construction and Reinforcement
−
−## Rectangular Duct
−
−Rectangular duct shall be fabricated and reinforced in conformance with ANSI/SMACNA 006-2020, Tables 1-3 through 1-11 and the associated construction details, for the declared pressure class. The following requirements supplement the SMACNA tables and represent the most frequently encountered field issues.
−
−Transverse joints shall be of a type listed in SMACNA for the declared pressure class and the duct size. Standing drive slip (S-drive), pocket drive slip, and companion angle joints are acceptable at low pressure classes for smaller duct sizes. Pittsburgh lock longitudinal seams are the standard for rectangular duct fabricated in the shop. Button punch snap lock is permitted for low-pressure duct only and is not acceptable for pressure class 2 in. w.g. and above. Grooved seams shall not be used for exterior or outdoor ductwork because moisture intrusion into the seam promotes corrosion.
−
−Flanged joint systems (TDC/TDF and equivalent roll-formed flanged systems) are acceptable transverse joint methods where listed by SMACNA for the declared pressure class. Flanged joint systems used at pressure class 2 in. w.g. and above shall use corner clips and gaskets of the type listed with the joint system, and the Contractor shall follow the manufacturer's installation instructions for bolt torque or clip spacing. Omitting corner clips or substituting uncertified generic corner pieces for a listed flanged joint system defeats the joint's pressure rating and is not acceptable.
−
−```datasheet
−label: Transverse Joint Type — Rectangular Duct
−type: select
−options:
− - "Flanged joint system (TDC/TDF or equivalent) — listed for pressure class"
− - "Companion angle flanges, bolted at spacing per SMACNA"
− - "Standing drive slip and pocket drive slip (low pressure, small duct only)"
−default: "Flanged joint system (TDC/TDF or equivalent) — listed for pressure class"
−```
−
−Reinforcement spacing and size shall conform to SMACNA for the declared pressure class. Intermediate reinforcement (angle iron, hat channel, or equivalent structural shape) shall be sized and spaced per the SMACNA reinforcement tables. The spacing intervals in SMACNA are maximum spacings; closer spacing is always acceptable. Where duct size or pressure class requires major reinforcement (spacing of 2 ft or less at high pressure), the Contractor shall verify that the reinforcement is attached through the duct wall to prevent the duct panel from separating from the reinforcement under pressure.
−
−Internal tie rods, where required by SMACNA for very large duct dimensions, shall be installed with backing plates at both duct walls to distribute the load and shall not be used as supports for internal elements such as damper blades or turning vanes.
−
−Duct aspect ratio shall be minimized consistent with the space constraints indicated on the drawings. High-aspect-ratio rectangular duct (width-to-height ratios above approximately 4:1) requires heavier gauge and closer reinforcement to resist panel deflection, increases friction loss per unit of cross-sectional area, and is more prone to drumming and vibration. Where layout permits, the Contractor should discuss with the Engineer whether a round or lower-aspect-ratio alternative achieves the required cross-sectional area within the available space.
−
−## Round and Spiral Duct
−
−Round duct shall be spiral-wound or longitudinal-seam welded in conformance with ANSI/SMACNA 006-2020. Spiral-wound duct is the standard fabrication method for round supply and return duct in commercial applications. Gauge for spiral round duct shall conform to SMACNA Table 3-1 for the declared pressure class. Round duct gauge requirements are lower than rectangular duct at equivalent size and pressure because the cylindrical form distributes internal pressure in pure hoop tension without bending stress on flat panels, which is the fundamental structural advantage of round duct.
−
−```datasheet
−label: Round Duct Fabrication Method
−type: radio
−options:
− - "Spiral wound, continuously welded seam"
− - "Longitudinal seam, welded or lock-formed"
−default: "Spiral wound, continuously welded seam"
−```
−
−Round fittings shall be fabricated from the same material and at least the same gauge as the connecting straight duct. Elbows for round duct shall have a centerline radius of at least 1.0 times the duct diameter (R/D ≥ 1.0) for low-pressure systems. Gored elbows are acceptable for sizes 12 in. diameter and above at the pressure class indicated; the number of gores (segments) shall be not less than three for 45-degree elbows and not less than four for 90-degree elbows for diameters 12 in. and below, and five-gore (or more) construction shall be used for larger diameters and high-pressure applications to reduce fitting loss coefficients.
−
−Tees and wye fittings for round duct shall be conical tees or 45-degree entry wyes rather than square-cut tee intersections. Square-cut tap connections create high entry loss and turbulence that significantly reduces branch airflow compared to design values and is one of the most common sources of air-balancing RFIs in round duct systems.
−
−## Flat-Oval Duct
−
−Flat-oval duct provides the flow cross-section advantage of round duct with a reduced installation height, making it useful where round duct cannot fit within structural bays but rectangular duct of equivalent area would be too large. Flat-oval duct shall be fabricated and reinforced in conformance with ANSI/SMACNA 006-2020, which introduced dedicated flat-oval tables in the 4th Edition for both positive and negative pressure applications.
−
−```datasheet
−label: Flat-Oval Duct
−type: radio
−options:
− - "Not used on this project"
− - "Used — fabricate per SMACNA flat-oval tables for declared pressure class"
−default: "Not used on this project"
−```
−
−Flat-oval fittings shall be fabricated to match the duct and shall conform to SMACNA. Transitions from flat-oval to rectangular or round shall be gradual — a total included angle of 30 degrees or less on each side is recommended to avoid flow separation — and shall be shown on shop drawings.
−
−# Fittings
−
−## General Requirements
−
−All fittings, including elbows, tees, wyes, offsets, transitions, and boot connections, shall be fabricated from the same material and at least the same gauge as the adjoining straight duct, at the declared pressure class. Fittings fabricated from lighter gauge sheet than the straight duct are a common field substitution and are not acceptable; they create the weakest points in the system at the locations of highest turbulence and dynamic pressure.
−
−## Rectangular Elbows
−
−Rectangular elbows shall be square-throat with turning vanes or radius-throat (curved elbows) as indicated on the contract drawings or as selected by the Contractor to meet the available space. Square-throat elbows without turning vanes have a loss coefficient of approximately 1.3 or higher and shall not be used in main supply or return ducts. Square-throat elbows with turning vanes reduce the loss coefficient to approximately 0.10 to 0.20 and are the standard for main duct elbows.
−
−Turning vanes shall be the double-wall airfoil type for all elbows in medium-pressure and high-pressure systems (pressure class 2 in. w.g. and above). Single-thickness vanes are acceptable in low-pressure systems for duct widths up to 36 in. Turning vanes shall be mounted in rails and shall be secured so that they cannot come loose under operating pressures. Turning vane spacing shall conform to SMACNA. Vane gauge shall be not less than 26 gauge for 2 in. vanes and not less than 24 gauge for 4 in. vanes, in conformance with SMACNA.
−
−Radius elbows shall have a centerline radius of at least 1.0 times the duct width (R/W ≥ 1.0) measured in the plane of the turn. The use of R/W < 0.75 creates significant flow separation on the inside of the elbow that persists for 10 to 15 duct diameters downstream and shall not be used except where specifically approved by the Engineer.
−
−```datasheet
−label: Rectangular Duct Elbow Type
−type: radio
−options:
− - "Square throat with double-wall airfoil turning vanes (medium/high pressure)"
− - "Square throat with single-wall turning vanes (low pressure, W ≤ 36 in.)"
− - "Radius elbow, R/W ≥ 1.0"
− - "Radius elbow, R/W ≥ 1.5 (low loss, shown on drawings)"
−default: "Square throat with double-wall airfoil turning vanes (medium/high pressure)"
−```
−
−## Transitions
−
−Transitions that change duct size shall have a total included angle not exceeding 30 degrees on each side for diverging (expansion) transitions to prevent flow separation. Converging (contraction) transitions are less sensitive to angle. Where space constraints require a transition angle greater than 30 degrees, turning vanes or a splitter may be required; the Contractor shall note on the shop drawing when a transition exceeds this guideline and obtain Engineer review.
−
−## Offsets and Conical Tee Connections
−
−Offsets shall be fabricated as two-piece or three-piece fittings to maintain reasonable transition angles. Connections from round main ducts to round branches shall use conical or saddle taps rather than raw hole taps. The high loss and turbulence of a raw hole tap (a drilled hole with no conical entry fitting) frequently causes branch-circuit air quantities to be significantly below design values and is one of the leading sources of TAB RFIs.
−
−# Flexible Duct
−
−## Listing and Classification
−
−Flexible duct shall be factory-made, listed to UL 181 as a Class 1 air duct. Class 1 requires a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 when tested in accordance with ASTM E84. Flexible air connectors (limited to 14 ft by UL listing) are not equivalent to flexible air ducts and shall not be used as a substitute where flexible duct is required.
−
−```datasheet
−label: Flexible Duct UL 181 Listing Required
−type: radio
−options:
− - "Yes — UL 181, Class 1 air duct listing required"
− - "Not applicable — no flexible duct on this project"
−default: "Yes — UL 181, Class 1 air duct listing required"
−```
−
−## Maximum Length
−
−Flexible duct runs shall be as short as practicable. The maximum allowable length of any single flexible duct run shall not exceed 6 ft, measured along the duct centerline in the installed position, except where the contract documents specifically permit longer runs for a defined purpose. Longer flexible duct runs increase resistance disproportionately relative to rigid duct, particularly when the duct is not fully extended, and create airflow deficiencies at the served outlets. Long runs of flex duct used in place of rigid duct to avoid coordination problems are a frequent source of complaints from building owners and are not acceptable.
−
−```datasheet
−label: Maximum Flexible Duct Run Length
−type: range
−unit: ft
−options:
− min: 2
− max: 14
− setpoints: [2, 4, 6, 8, 10, 14]
−default: 6
−```
−
−## Extension and Sag
−
−Flexible duct shall be installed fully extended, with the inner core pulled taut and without excess length coiled or looped in the ceiling. Excess length increases friction loss approximately as the square of the length ratio and is the single most common installation defect in flexible duct systems. The installed duct shall not be compressed or convoluted. Sag between supports shall not exceed 1/2 in. per foot of horizontal run.
−
−## Bends and Turns
−
−Bends in flexible duct shall have a centerline bend radius of at least 1.0 times the duct diameter. The flex duct shall be allowed to run straight for a minimum of 12 in. from any plenum, collar, or rigid duct connection before making a bend, to allow the flow to develop before the direction change. Tight bends immediately at the collar connection are a leading cause of poor airflow to diffusers and shall not be permitted.
−
−## Support and Hanger Spacing
−
−Flexible duct shall be supported at intervals not exceeding 4 ft on horizontal runs in conformance with ANSI/SMACNA 006-2020, Fourth Edition. Support straps or hangers shall be at least 1.5 in. wide and shall not constrict the inner core. Pinching or cinching the support strap tight enough to reduce the internal diameter is not acceptable. Flexible duct shall not sag more than 1/2 in. per foot of unsupported span.
−
−```datasheet
−label: Flexible Duct Hanger Maximum Spacing
−type: range
−unit: ft
−options:
− min: 2
− max: 4
− setpoints: [2, 3, 4]
−default: 4
−```
−
−## Connections
−
−Flexible duct connections to rigid duct, air terminal units, and air distribution devices shall be made using sheet-metal collars, sleeves, or flexible connections designed for the purpose. The inner core jacket shall extend over the collar a minimum of 1.5 in. and shall be secured with a draw band (worm-gear clamp). The outer insulation jacket and vapor barrier shall then be drawn over the connection, overlapping the collar by at least 2 in., and secured with a second draw band. The connection shall be sealed with UL 181B listed tape or mastic. Connections made with duct tape (pressure-sensitive cloth-backed tape) are not acceptable for any application; cloth-backed duct tape is not UL 181B listed and degrades and fails within a few years of installation.
−
−# Duct Insulation and Liner
−
−## Duct Liner
−
−Duct liner is applied to the interior surface of the duct and provides both thermal insulation and sound attenuation. The primary acoustical benefit of liner is the reduction of fan and system-generated noise transmitted through the duct walls.
−
−Duct liner shall conform to ASTM C1071 and shall have a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 per ASTM E84 when tested as an assembly. The liner face velocity shall not exceed the liner manufacturer's maximum recommended face velocity; exceeding face velocity limits can cause liner fibers to erode and enter the airstream, which represents an indoor air quality concern. The standard face velocity limit for most fibrous glass liners is 6,000 ft/min; the Engineer shall specify a lower limit or a different liner material where system velocities exceed this value.
−
−Liner shall not be installed in supply duct downstream of humidifiers or in portions of the system subject to persistent moisture accumulation (condensation zones, kitchen exhaust, etc.) because moisture degrades fibrous glass liner over time and promotes microbial growth. In moisture-prone zones, smooth-interior unlined duct with external insulation is preferred.
−
−```datasheet
−label: Duct Liner
−type: radio
−options:
− - "Not used — external insulation only"
− - "Provided — ASTM C1071, 1 in. thick (R-4 nominal)"
− - "Provided — ASTM C1071, 1.5 in. thick (R-6 nominal)"
− - "Provided — ASTM C1071, 2 in. thick (R-8 nominal)"
−default: "Not used — external insulation only"
−```
−
−Liner shall be adhered continuously to the duct interior surface with a water-resistant adhesive, and mechanical fasteners (stick pins with clips or weld pins) shall be installed at a spacing not exceeding 18 in. in each direction to prevent the liner from separating from the duct wall. All liner edges at duct openings, elbows, and access doors shall be coated or sealed to prevent erosion of the exposed edge into the airstream. Impaled-pin fastener caps shall be the same material as the liner facing.
−
−Liner thickness shall be as shown on the contract documents. Where not shown, a minimum of 1 in. thick liner shall be provided. The specified duct dimension is the clear inside dimension after liner installation; the duct shall be fabricated oversize to maintain the design airflow area. Fabricating duct to the design dimension and then applying liner inside reduces the cross-sectional area and increases velocity beyond design values, and is not acceptable.
−
−## External Duct Insulation
−
−External duct insulation (duct wrap) shall be applied to ducts in unconditioned spaces, in semi-conditioned spaces, in ceiling plenums not serving as return air plenums, and in all locations outside the conditioned envelope, in conformance with ASHRAE 90.1 for the applicable climate zone and duct location.
−
−```datasheet
−label: External Duct Insulation R-Value — Ducts in Unconditioned Spaces
−type: select
−unit: h·ft²·°F/Btu
−drawing_ref: true
−options:
− - "R-4.2"
− - "R-6"
− - "R-8"
− - "R-12"
−default: "R-6"
−```
−
−```datasheet
−label: External Duct Insulation R-Value — Ducts Outdoors or in Ventilated Attics
−type: select
−unit: h·ft²·°F/Btu
−drawing_ref: true
−options:
− - "R-6"
− - "R-8"
− - "R-12"
−default: "R-8"
−```
−
−ASHRAE 90.1 (current edition) establishes minimum R-values for ducts by location and climate zone. For Climate Zones 1 through 3, R-6 is a common minimum for unconditioned space ducts; for Climate Zones 4 and above, R-8 is often required for unconditioned spaces and R-12 for outdoor ducts. The Engineer shall specify the required R-value by location on the contract documents based on the project climate zone; the above defaults are representative for Climate Zone 3B/4A and shall be verified for the specific project.
−
−External duct insulation shall conform to ASTM C553 (mineral fiber blanket) or other approved material. Insulation shall have a factory-applied vapor retarder jacket for supply air duct systems carrying conditioned air in unconditioned spaces. The vapor retarder shall have a permeance of 0.10 perm or less (Class II vapor retarder). Joints in the vapor retarder shall be sealed with tape compatible with the jacket material to maintain a continuous vapor barrier. Incomplete or punctured vapor retarders on cold-air supply ducts in humid unconditioned spaces will result in condensation, dripping, and over time insulation deterioration and microbial growth.
−
−Installed insulation thickness to achieve the specified R-value shall account for the compression factor. For flexible duct wrap installed on rectangular duct, the installed thickness is approximately 75 percent of nominal thickness due to compression at corners and supports; the selected product nominal thickness shall provide the required R-value at installed thickness, not at nominal thickness.
−
−```datasheet
−label: External Insulation Vapor Retarder Jacket
−type: radio
−options:
− - "Factory-applied FSK (foil-scrim-kraft) jacket, ≤ 0.10 perm"
− - "Factory-applied reinforced aluminum foil jacket, ≤ 0.10 perm"
− - "Not required — duct in conditioned space"
−default: "Factory-applied FSK (foil-scrim-kraft) jacket, ≤ 0.10 perm"
−```
−
−# Duct Sealants
−
−## General Sealant Requirements
−
−All duct sealing materials shall be compatible with the duct material and shall remain effective at the operating temperature and pressure of the system. Sealants shall be applied to clean, dry, dust-free surfaces; applying sealant to dusty, oily, or damp duct surfaces prevents adhesion and causes early sealant failure, which is a leading cause of duct leakage test failures on projects where sealant was applied but not to clean surfaces.
−
−## Mastic Sealant
−
−Water-based mastic is the preferred sealant for transverse joints, longitudinal seams, and duct wall penetrations in metal ductwork. Mastic shall conform to UL 181A-M for application to rigid ducts. Mastic shall be applied in a continuous bead and tooled to fill the joint completely, with the excess feathered onto the adjacent duct surface. The dry-film thickness shall conform to the manufacturer's recommendation; a single thin coat is not sufficient to fill gaps at flanged joints.
−
−Where gaps exceed 1/4 in. at any joint, mastic alone is insufficient and the gap shall be bridged by applying fiberglass mesh tape before applying mastic. The mastic shall be worked through the mesh fabric and shall fully embed the fabric. Large gaps that cannot be closed by mesh-reinforced mastic indicate a fabrication defect; joints with gaps exceeding 3/4 in. shall be re-fabricated or re-fitted, not merely bridged with mesh and mastic.
−
−```datasheet
−label: Primary Sealant Type — Metal Ductwork
−type: radio
−options:
− - "Water-based mastic, UL 181A-M listed"
− - "Spray-applied duct sealant, UL 181A-M listed (shop application)"
− - "Aerosolized sealant injected into installed duct (remedial use only)"
−default: "Water-based mastic, UL 181A-M listed"
−```
−
−## Foil Tape
−
−Pressure-sensitive foil tape, listed to UL 181A-P, is acceptable as a supplement to mastic but shall not be used as the sole sealant at transverse joints in ducts at pressure class 2 in. w.g. and above. Foil tape is appropriate for sealing longitudinal seams on spiral round duct and for patching small punctures. Cloth-backed duct tape is not UL 181A or 181A-P listed and is not acceptable for ductwork sealing in any application.
−
−## Flexible Duct Connections
−
−Sealants and tapes for flexible duct connections shall be listed to UL 181B-M or UL 181B-FX, respectively, conforming to the applicable closure class. Connections at flexible duct collars shall use draw bands and UL 181B listed tape or mastic as described in the flexible duct section.
−
−# Accessories
−
−## Fire Dampers
−
−Fire dampers shall be installed in ductwork where ducts penetrate or terminate at openings in fire-rated assemblies (walls, floors, and partitions) required to have a fire-resistance rating of 2 hours or more, in accordance with NFPA 90A and the IMC. Fire dampers shall be listed to UL 555, suitable for dynamic or static duty as required by the installation condition. Where the fan serves the duct without an upstream isolation point, dynamic-rated dampers (rated while the air system is running) shall be used; static dampers may only be used where the fire-safety system shuts down the fan before the damper closes.
−
−Fire dampers shall be rated for a minimum of 1.5 hours or 3 hours as required by the fire-resistance rating of the assembly being penetrated, in conformance with the building code. The Contractor shall verify the required rating for each damper location from the fire-rated assembly schedule on the architectural drawings.
−
−```datasheet
−label: Fire Damper Rating
−type: radio
−options:
− - "1.5 hours (for assemblies requiring 2-hour rating per IBC/IMC)"
− - "3 hours (for assemblies requiring 3-hour or greater rating)"
−default: "1.5 hours (for assemblies requiring 2-hour rating per IBC/IMC)"
−```
−
−```datasheet
−label: Fire Damper Duty Rating
−type: radio
−options:
− - "Dynamic (fan operates until damper closes — standard for VAV systems)"
− - "Static (fan shut down before damper closes)"
−default: "Dynamic (fan operates until damper closes — standard for VAV systems)"
−```
−
−Fire dampers shall be installed in the plane of the rated assembly in conformance with their UL listing and the manufacturer's installation instructions. The damper shall be installed using a sleeve transition or breakaway connection so that thermal expansion of the duct does not impose loads on the rated assembly. Retaining angles or frames shall be provided in conformance with UL 555 listing requirements to prevent the damper from being displaced when the duct collapses under fire conditions.
−
−Each fire damper shall be equipped with an access door located immediately adjacent to the damper on the side that provides access to the fusible link or actuator and the reset mechanism. Access door size shall be not less than 16 in. × 16 in., or not less than 18 in. in diameter for round duct, sufficient to allow inspection, link replacement, and damper reset without removing building finishes. Access panels in fire-rated assemblies shall be rated to match the assembly.
−
−## Smoke Dampers
−
−Smoke dampers shall be listed to UL 555S and shall be installed where required by NFPA 90A, the IMC, and the building fire protection and life safety design. Smoke dampers shall be installed in ductwork at penetrations of smoke barriers and in HVAC systems with a capacity exceeding 15,000 cfm to isolate the air-handling equipment from the duct distribution system in a smoke-control event.
−
−Smoke dampers shall be equipped with a suitable actuator — electric or pneumatic — capable of closing within the time required by the system smoke-control sequence, and shall be supervised by the fire alarm system in conformance with the Life Safety Contractor's requirements. Smoke dampers shall be capable of holding closed against the maximum system pressure and of operating over the full temperature range of the installation.
−
−```datasheet
−label: Smoke Damper Actuator Type
−type: radio
−options:
− - "Electric, 24 VAC, spring return fail-closed"
− - "Electric, 120 VAC, spring return fail-closed"
− - "Pneumatic, fail-closed"
−default: "Electric, 24 VAC, spring return fail-closed"
−```
−
−Each smoke damper shall be provided with an access door on each side of the assembly it penetrates (or on the side with the actuator) that complies with NFPA 90A access requirements. Access to smoke dampers shall not require removal of permanent construction. The fire alarm contractor shall coordinate actuator wiring and supervisory connections with the HVAC Contractor; the HVAC Contractor is responsible for installing the damper and the access door and for providing the rough-in provisions required by the actuator manufacturer.
−
−## Combination Fire and Smoke Dampers
−
−Where both a fire rating and smoke control are required at a single penetration, a combination fire/smoke damper listed to both UL 555 and UL 555S shall be installed. Combination dampers shall comply with the requirements of both this section and the fire damper and smoke damper sections above.
−
−## Volume Control Dampers
−
−Volume control dampers (manual balancing dampers) shall be installed in branch ducts at locations shown on the contract drawings to allow balancing of airflow. Volume control dampers shall be opposed-blade (for control applications) or single-blade (for zone shutoff) type as shown on the contract drawings. Dampers shall be equipped with quadrant handles with locking nuts that maintain the set position permanently after balancing. The Contractor shall provide all volume control dampers at the locations shown on the drawings and shall not omit dampers as a cost-reduction measure; missing volume control dampers prevent the TAB contractor from balancing the system and are a frequent source of punch-list items.
−
−```datasheet
−label: Volume Control Damper Blade Type
−type: radio
−options:
− - "Opposed blade (for throttling and control)"
− - "Single blade / butterfly (for zone shut-off)"
−default: "Opposed blade (for throttling and control)"
−```
−
−## Access Doors in Ductwork
−
−Access doors shall be provided in the duct at locations indicated on the contract documents and at every fire damper, smoke damper, combination fire/smoke damper, and flow-measuring station. Access doors shall also be provided at coil access points, filter frames, and other components requiring maintenance access through the duct wall.
−
−Access doors shall be airtight, shall be hinged or removable, and shall be constructed of the same material and at least the same gauge as the duct they serve. For pressure class 2 in. w.g. and above, access doors shall incorporate a gasket around the perimeter to prevent leakage. Access door frames shall be sealed to the duct with mastic before installation. Access door size shall be not less than 12 in. × 12 in. for ducts up to 24 in. in the smaller dimension, and shall be not less than 18 in. × 18 in. for larger ducts to permit personnel to work inside. Size shall in all cases be sufficient to inspect, test, and reset the device served.
−
−```datasheet
−label: Access Door Minimum Size
−type: radio
−unit: in
−options:
− - "12 × 12 (ducts ≤ 24 in. smaller dimension)"
− - "18 × 18 (ducts > 24 in. smaller dimension)"
− - "As shown on drawings (custom size for specific access requirement)"
−default: "12 × 12 (ducts ≤ 24 in. smaller dimension)"
−```
−
−# Hangers and Supports
−
−## General Support Requirements
−
−Ductwork shall be supported from the building structure — concrete structure, steel framing, or wood framing — using hangers, trapeze supports, or wall brackets designed and installed for the weight of the duct, the insulation, and any devices mounted on or in the duct. Supports shall not be attached to piping, conduit, or other mechanical and electrical systems that are themselves supported from structure; cross-supporting between different systems creates loads on systems not designed for them and is not permitted.
−
−Support spacing, rod diameter, and trapeze member size shall conform to SMACNA HVAC Duct Construction Standards, Tables 4-1 through 4-4, for the duct size and pressure class. The SMACNA hanger tables provide maximum spacing and minimum rod/strap sizes; closer spacing is always acceptable and may be required at elbows, transitions, and heavy accessories.
−
−```datasheet
−label: Maximum Hanger Spacing — Rectangular Duct
−type: range
−unit: ft
−options:
− min: 4
− max: 10
− setpoints: [4, 5, 8, 10]
−default: 8
−```
−
−```datasheet
−label: Maximum Hanger Spacing — Round and Flat-Oval Duct
−type: range
−unit: ft
−options:
− min: 8
− max: 12
− setpoints: [8, 10, 12]
−default: 10
−```
−
−Additional supports shall be provided within 2 ft of each elbow, transition, and duct intersection, and within 2 ft of each end of flexible duct runs, in conformance with SMACNA. Ductwork shall not be supported by the suspended ceiling system; the duct weight shall be carried directly to structure by independent hangers.
−
−## Hanger Types
−
−Trapeze hangers shall be used for rectangular duct wider than 42 in. and for duct carrying heavy accessories such as dampers, coil sections, or fan-powered boxes. Trapeze lower members shall be steel angle or strut channel of sufficient size to span the duct width without excessive deflection. Upper rod sizes shall be selected from SMACNA Table 4-2.
−
−Strap hangers (galvanized steel flat strap) shall be acceptable for rectangular duct up to 42 in. wide where the duct is supported directly from structure without a long rod, and for round and oval duct. Strap width and gauge shall conform to SMACNA.
−
−Hanger rods shall be galvanized steel threaded rod, with nuts and lock washers at all connection points. Hanger rods shall be attached to the building structure by means appropriate to the structural material — concrete anchors for concrete, drilled and bolted connections for steel framing, or wood screws for wood framing. Power-actuated fasteners shall not be used to attach duct hangers to structural members without Engineer approval.
−
−```datasheet
−label: Hanger Type — Rectangular Duct
−type: radio
−options:
− - "Trapeze (lower angle with upper rods) — ducts over 42 in. wide"
− - "Flat strap (galvanized) — ducts ≤ 42 in. wide"
− - "Fabricated bracket — wall-mounted duct"
−default: "Trapeze (lower angle with upper rods) — ducts over 42 in. wide"
−```
−
−## Seismic Bracing
−
−Where the project is located in a seismic design category (SDC) requiring seismic restraint of mechanical systems, ductwork shall be laterally braced in conformance with SMACNA Seismic Restraint Manual — Guidelines for Mechanical Systems and the requirements of the adopted building code. Seismic bracing shall be designed by a licensed structural or mechanical engineer where required by the local jurisdiction. The Contractor shall not omit seismic bracing to reduce cost without a written change in scope; SDC B and higher typically requires lateral restraint of ducts larger than specified threshold sizes.
−
−```datasheet
−label: Seismic Bracing Required
−type: radio
−options:
− - "Yes — per SMACNA Seismic Restraint Manual and local code"
− - "No — project SDC does not require duct bracing"
−default: "Yes — per SMACNA Seismic Restraint Manual and local code"
−```
−
−## Vibration Isolation at Equipment Connections
−
−Flexible connections shall be provided between ductwork and air-handling units, fans, fan coil units, and other rotating equipment to prevent transmission of vibration and noise into the duct system. Flexible connections shall be of neoprene or canvas reinforced fabric, not less than 3 in. long, and shall be installed without tension or compression in the neutral position with the equipment operating. The ductwork immediately adjacent to the air-handling unit shall be independently supported so that the weight of the duct does not bear on the flexible connection or on the equipment casing.
−
−```datasheet
−label: Flexible Connections at Equipment
−type: radio
−options:
− - "Neoprene-coated woven glass fiber fabric, 3 in. minimum length"
− - "Canvas duck fabric (not for outdoor use), 3 in. minimum length"
−default: "Neoprene-coated woven glass fiber fabric, 3 in. minimum length"
−```
−
−# Installation
−
−## Coordination and Sequencing
−
−Before fabricating shop ductwork, the Contractor shall verify that the routing shown on the contract drawings is achievable within the structure, existing utilities, and other mechanical and electrical systems. Where interferences exist, the Contractor shall participate in the BIM coordination process or manual coordination process established for the project and shall resolve interferences before fabrication. Field modifications to duct routing made after fabrication to avoid interferences result in non-standard fittings, increased field labor, and delays; early coordination prevents these problems.
−
−## Clearances
−
−Ductwork shall be installed with clearances conforming to the IMC. Clearances from combustible construction shall be maintained as required by NFPA 90A. Where insulated ductwork is installed adjacent to combustible construction, the clearance shall be measured to the outer face of the insulation. Where uninsulated metal ductwork is installed near combustible materials, the NFPA 90A minimum clearances shall be maintained.
−
−The Contractor shall maintain a minimum 1-in. clearance between insulated ductwork and any other building system (piping, conduit, structure) to avoid compression of duct insulation and to allow future maintenance access. Duct-to-duct clearances shall allow for insulation installation and maintenance access to dampers and other devices.
−
−## Hangers — Installation Details
−
−All threaded rod connections shall be made up wrench-tight with jam nuts to prevent vibration-induced loosening over time. Nuts shall be installed above and below the trapeze lower member to prevent the lower member from sliding. Duct straps shall be attached to the duct sides, not the bottom, for rectangular duct, to prevent the strap from cutting into the duct bottom under load. Round duct strap hangers shall be wide enough to distribute load without deforming the duct cylinder.
−
−## Sealant Application
−
−Sealant shall be applied in conformance with this standard and the sealant manufacturer's published application instructions. All surfaces to be sealed shall be cleaned of dirt, oil, and loose metal burrs before sealant application. Sealant shall be applied before the duct is insulated; sealing over installed insulation is not acceptable.
−
−For flanged (TDC/TDF) transverse joints, mastic shall be applied to the interior face of both flanges before assembly, and a bead shall be applied to the exterior face of the assembled joint. Corner clips and any visible gaps shall be masked with mastic. The common practice of applying mastic only to the exterior of an already-assembled flanged joint without interior sealant is not acceptable for Seal Class B or Class A systems; it does not seal the contact face between the flanges.
−
−For Pittsburgh lock longitudinal seams, mastic shall be applied continuously to the exterior of the seam. For spiral round duct, the spiral seam is welded in manufacture and does not require additional field sealing; the field joints (slip-and-drive or flanged) shall be sealed with UL 181A listed tape or mastic.
−
−## Duct Liner Installation
−
−Liner shall be installed per the liner manufacturer's instructions and SMACNA HVAC Duct Construction Standards duct liner details. Adhesive shall be applied to 100 percent of the liner surface for duct surfaces facing the airstream, with particular care at corners. Mechanical fasteners shall be installed through the liner into the duct wall with caps that prevent the liner from pulling free of the fastener. At fittings, liner shall be mitered and fitted to maintain a smooth interior surface; gaps in liner at elbow throats and heels allow airstream exposure of raw liner edges that erode and delaminate over time.
−
−## Fire Damper Installation
−
−Fire dampers shall be installed in strict conformance with the UL listing requirements for the specific damper series, the damper manufacturer's installation instructions, and NFPA 90A. No installation method, orientation, or accessory configuration that deviates from the listing is acceptable without a specific listing expansion or special engineering approval from the AHJ.
−
−The Contractor shall coordinate with the structural and architectural trades to ensure that the rated assembly framing is in place before the damper sleeve is installed, that the sleeve is installed plumb and square in the rated assembly, and that the fire-stopping of the annular space between the sleeve and the assembly is completed after damper installation. Fire damper locations shall be marked on the as-built drawings with damper tag numbers corresponding to the damper schedule.
−
−Fusible links in fire dampers shall not be installed until after the duct system construction, cleaning, and leakage testing are complete. Installing fusible links during construction exposes them to heat, paint overspray, and mechanical damage and is a common cause of damper failures during commissioning.
−
−## Cleanliness
−
−The interior of duct systems shall be protected from contamination during construction. Duct openings left in place during construction shall be sealed with cardboard, plastic sheeting, or sheet-metal caps to prevent construction debris — concrete dust, drywall dust, masonry debris, insulation fibers — from entering the duct. Duct protection is a routine construction requirement, not an optional quality measure; ducts contaminated with construction debris require costly post-construction cleaning and can cause fan damage when the system is first operated.
−
−The Contractor shall inspect ductwork before insulation is applied and before access doors are closed and shall remove all debris, tools, and foreign objects. Where the owner requires post-construction duct cleaning per NADCA standards, the cleaning contractor's work is a separate scope; this standard governs the Contractor's obligation to keep the duct clean during construction.
−
−# Leakage Testing
−
−## Purpose and Scope
−
−Leakage testing verifies that the duct system meets the seal class specified and, where the energy code requires it, meets the maximum leakage rate allowed under ASHRAE 90.1. Testing shall be conducted in conformance with ANSI/SMACNA 016-2012, HVAC Air Duct Leakage Test Manual, Second Edition.
−
−Leakage testing shall be performed before duct systems are insulated, before access doors are permanently closed, and before ceilings are installed or duct is otherwise made inaccessible. Performing leakage testing after insulation installation reduces the ability to locate and seal leaks when the test fails, and is not acceptable.
−
−```datasheet
−label: Leakage Testing Required
−type: radio
−options:
− - "Yes — required for all pressure class 2 in. w.g. and above systems"
− - "Yes — required for all duct systems (including low-pressure) per energy code"
− - "No — project conditions exempt (confirm with Engineer)"
−default: "Yes — required for all pressure class 2 in. w.g. and above systems"
−```
−
−## Test Sections
−
−Testing shall be performed on sections of the duct system totaling a minimum of 25 percent of the total duct surface area, selected to include the sections most likely to leak — high-pressure zones, sections with many joints, and sections near fan connections. Where a project-specific energy code requires testing of a larger percentage, the larger percentage governs. The leakage test plan submitted by the Contractor shall identify the test sections and the rationale for selection before testing begins.
−
−## Test Method
−
−The duct section to be tested shall be isolated by sealing open ends (diffuser and grille openings, flanged connections not yet made, branch openings) with temporary caps or blank-off plates. The test fan and flowmeter shall be connected to the isolated section. The section shall be pressurized to the test pressure (equal to the declared pressure class for the duct system) and the leakage flow rate shall be measured in cfm using a calibrated flowmeter.
−
−Test equipment shall be calibrated. The Contractor shall provide documentation of the calibration date for the flowmeter and pressure gauges used in the test. Calibration shall be current within one year or within the instrument manufacturer's recommended calibration interval, whichever is shorter.
−
−## Acceptance Criteria
−
−Maximum permitted leakage (Lmax) shall be calculated per the SMACNA leakage test manual formula:
−
−**Lmax = CL × P^0.65**
−
−Where: Lmax is the maximum leakage rate in cfm per 100 ft² of duct surface area; CL is the duct leakage class; and P is the test pressure in inches water column equal to the declared pressure class.
−
−The duct leakage class (CL) values from ANSI/SMACNA 016-2012 (Second Edition) for the declared seal class are:
−
−| Seal Class | CL — Rectangular | CL — Round and Flat-Oval |
−|------------|-------------------|--------------------------|
−| Class A | 4 cfm/100 ft² at 1 in. w.g. | 2 cfm/100 ft² at 1 in. w.g. |
−| Class B | 8 cfm/100 ft² at 1 in. w.g. | 4 cfm/100 ft² at 1 in. w.g. |
−| Class C | 16 cfm/100 ft² at 1 in. w.g. | 8 cfm/100 ft² at 1 in. w.g. |
−
−```datasheet
−label: Maximum Leakage Class (CL) — Rectangular Duct
−type: select
−unit: cfm/100 ft² at 1 in. w.g.
−options:
− - "CL = 4 (Seal Class A)"
− - "CL = 8 (Seal Class B)"
− - "CL = 16 (Seal Class C)"
−default: "CL = 8 (Seal Class B)"
−```
−
−```datasheet
−label: Maximum Leakage Class (CL) — Round and Flat-Oval Duct
−type: select
−unit: cfm/100 ft² at 1 in. w.g.
−options:
− - "CL = 2 (Seal Class A)"
− - "CL = 4 (Seal Class B)"
− - "CL = 8 (Seal Class C)"
−default: "CL = 4 (Seal Class B)"
−```
−
−Where ASHRAE 90.1 or the energy code imposes a maximum total system leakage expressed as a percentage of total supply airflow or as a fixed cfm/ft² value, the Engineer shall convert that requirement to a CL-equivalent and specify the more stringent of the SMACNA CL or the energy code limit on the contract documents.
−
−## Remediation and Re-Test
−
−Where a test section fails to meet the acceptance criterion, the Contractor shall locate the leaks by listening, feeling with a gloved hand, or using a soap solution or smoke pencil while the section is under pressure. All identified leaks shall be sealed with mastic or tape per this standard. After remediation, the section shall be re-tested to confirm that the corrected leakage is within the acceptance criterion. Re-testing shall be performed before insulation is applied to the repaired area.
−
−```datasheet
−label: Leak Location Method
−type: radio
−options:
− - "Manual (listening and touch while pressurized)"
− - "Soap solution or smoke pencil while pressurized"
− - "Ultrasonic leak detector"
−default: "Soap solution or smoke pencil while pressurized"
−```
−
−## Test Reporting
−
−The testing technician shall prepare a written test report for each tested section documenting the section location and tag, the duct surface area of the section, the test pressure, the measured leakage flow rate, the calculated Lmax, the pass/fail determination, the leaks found and corrective action taken, and the post-correction re-test result. Reports shall be signed by the testing technician and included in the closeout submittal.
−
−# Delivery, Storage, and Handling
−
−Shop-fabricated ductwork shall be protected during transportation to the site with caps or plugs on all open ends. Duct sections shall be stored indoors or under weatherproof cover at the site; duct stored outdoors without cover accumulates rainwater, dirt, and construction debris that is difficult to remove once the duct is installed. Flexible duct shall be stored in its original packaging, indoors, and shall not be stored where it will be walked upon or subjected to loads that deform the inner core.
−
−Liner and external insulation shall be stored in dry conditions and protected from moisture. Wet insulation loses R-value, may support microbial growth, and if installed wet will dry unevenly and may separate from the duct face. Insulation that has been saturated shall be discarded and replaced; it shall not be dried and re-installed.
−
−Duct sections, fittings, and accessories shall be handled with care during installation to avoid denting, crushing, or deforming the duct. Rectangular duct used as a stepladder or work surface is damaged and shall not be installed. Workers shall not walk on flat-oval or round duct.
−
−# Identification
−
−Ductwork shall be identified with system type and direction of flow at each branch, at each access door, and at intervals not exceeding 50 ft on straight runs, in conformance with SMACNA and the IMC. Identification shall include the system designation (SAL-1, RA-2, EA-3, etc.) and an airflow direction arrow. Fire dampers and smoke dampers shall be tagged with the damper tag number matching the damper schedule. Access doors shall be labeled with the device served.
−
−Insulated ductwork identification shall be placed on the outer face of the insulation jacket using stencil or adhesive label. Color coding is not required by SMACNA but where the Engineer specifies a color-coding scheme for system types, the Contractor shall apply the designated colors.
−
−# Warranty
−
−The Contractor shall warrant the ductwork installation, including fabrication, seams, joints, sealing, insulation, hangers, and accessories, against defects in materials and workmanship for a period from the date of substantial completion as specified below. The warranty shall cover failures, excessive leakage, hanger failures, sealant failures, and insulation separation from duct surfaces. Damper actuators and other mechanical accessories shall carry the manufacturer's warranty, which the Contractor shall assign to the Owner at project closeout.
−
−```datasheet
−label: Ductwork Installation Warranty Period
−type: select
−options:
− - "1 year from substantial completion"
− - "2 years from substantial completion"
−default: "1 year from substantial completion"
−```
−
−Where leakage testing results that are borderline (passing but within 10 percent of the acceptance criterion) are accepted, the Engineer may require a re-test during the warranty period to confirm that seasonal temperature cycles, building settlement, and sealant aging have not caused the leakage rate to increase to a failing value. Re-testing under warranty shall be at the Contractor's expense. The Contractor shall maintain access to all tested duct sections throughout the warranty period by keeping access doors clear of finishes, equipment, and storage.
+---
+title: HVAC Ductwork
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: Metal and flexible ductwork for low-pressure, medium-pressure, and high-pressure HVAC air distribution systems in commercial, institutional, and industrial buildings. Covers rectangular, round, flat-oval, and flexible duct; pressure and seal classifications; gauge and reinforcement; fittings and turning vanes; duct liner and external insulation; sealants; fire and smoke dampers; access doors; hangers and supports; leakage testing; and field verification. Applies to new construction and major renovation of supply, return, exhaust, and outside-air distribution systems.
+ Not intended for: Kitchen exhaust grease duct systems (see [[sync/kitchen-exhaust-systems]]); industrial process ventilation conveying particulates, corrosive gases, or high-temperature products; fume hood exhaust systems; pneumatic tube systems; chilled-water or hydronic piping insulation (see [[sync/building-thermal-insulation]]); air-handling unit casing and coil sections (see [[sync/air-handling-units]]); air terminal units (see [[sync/air-terminal-units]]); air distribution devices at duct outlets (see [[sync/hvac-air-distribution-devices]]); testing, adjusting, and balancing of the completed air distribution system (see [[sync/testing-adjusting-and-balancing]]).
+---
+
+# Scope {toc}
+
+## This standard covers the materials, fabrication, installation, sealing, insulation, support, testing, and field verification of HVAC ductwork systems for commercial and institutional buildings. {note}
+
+## All duct construction shall conform to ANSI/SMACNA 006-2020, HVAC Duct Construction Standards — Metal and Flexible, Fourth Edition, and shall satisfy the requirements of the adopted edition of the International Mechanical Code (IMC), NFPA 90A, and ASHRAE 90.1 for the jurisdiction of the project.
+
+## Where these references conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+## Why a clear baseline matters: ductwork is the backbone of every air distribution system, and undersized or leaky ductwork wastes fan energy, fails to deliver design airflow, causes noise and vibration, and creates thermal comfort complaints that are difficult and expensive to correct after construction, while over-specified ductwork adds unnecessary cost and weight; this standard establishes a clear, consistent baseline that delivers the design pressure class, the design leakage class, and the design insulation performance — nothing less, nothing more — with the quality controls and testing needed to verify that the installed system performs as intended. {note}
+
+## Coordinate the duct system with the air-handling unit connections specified in [[sync/air-handling-units]], with air terminal unit connections in [[sync/air-terminal-units]], and with the outlet and inlet devices in [[sync/hvac-air-distribution-devices]].
+
+## Coordinate leakage testing, flow measurement, and air-balancing activities with [[sync/testing-adjusting-and-balancing]].
+
+## Coordinate thermal insulation of ducts outside the building with [[sync/building-thermal-insulation]] where project-specific requirements supplement this standard.
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest editions of the following standards adopted by the project jurisdiction.
+## Where a specific edition is referenced in contract documents or by the local building code, that edition shall govern.
+
+| Standard | Title |
+|----------|-------|
+| ANSI/SMACNA 006-2020 | HVAC Duct Construction Standards — Metal and Flexible, Fourth Edition |
+| ANSI/SMACNA 016-2012 | HVAC Air Duct Leakage Test Manual, Second Edition |
+| ASHRAE 90.1 | Energy Standard for Buildings Except Low-Rise Residential Buildings (current adopted edition) |
+| NFPA 90A | Standard for the Installation of Air-Conditioning and Ventilating Systems (current adopted edition) |
+| IMC | International Mechanical Code (current adopted edition) |
+| UL 181 | Standard for Factory-Made Air Ducts and Air Connectors |
+| UL 181A | Standard for Closure Systems for Use with Rigid Air Ducts |
+| UL 181B | Standard for Closure Systems for Use with Flexible Air Ducts and Air Connectors |
+| UL 555 | Standard for Fire Dampers |
+| UL 555S | Standard for Smoke Dampers |
+| ASTM A653 | Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated by the Hot-Dip Process |
+| ASTM B209 | Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate |
+| ASTM A240 | Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and General Applications |
+| ASTM C1071 | Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material) |
+| ASTM C553 | Standard Specification for Mineral Fiber Blanket Thermal Insulation for Commercial and Industrial Applications |
+| ASTM E84 | Standard Test Method for Surface Burning Characteristics of Building Materials |
+| NFPA 90B | Standard for the Installation of Warm Air Heating and Air-Conditioning Systems |
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following for the Engineer's review and return prior to procurement or installation of the corresponding duct system components.
+
+### No fabrication or installation shall proceed on a duct system or duct component until the associated submittal has been reviewed and returned with no outstanding engineering questions.
+
+## Action Submittal Items {toc}
+
+### The Contractor shall submit the following action submittal items:
+
+- Product data for each duct material, including the metal specification, coating designation, and gauge schedules proposed for each pressure class
+- Product data for duct sealants, tapes, and mastics, including the applicable UL 181, UL 181A, or UL 181B listing, the manufacturer's cure and surface preparation requirements, and the working temperature range
+- Product data and cut sheets for flexible duct, including the UL 181 listing, the insulation R-value, the vapor jacket material, and the maximum recommended bend radius
+- Product data for fire dampers and smoke dampers, including UL 555 and UL 555S listings, the pressure class, the blade orientation, the actuator type, and the access requirements
+- Product data for duct liner and external duct wrap insulation, including ASTM C1071 conformance for liner, the R-value, the facing material, and the flame-spread and smoke-developed indices
+- Leakage test plan, prepared before testing begins, identifying the duct sections to be tested, the test pressures, the instruments to be used, and the acceptance criteria
+- Shop drawings showing duct routing, offset dimensions, fitting configurations, hanger locations, access door locations, and the coordination of duct penetrations with fire-rated assemblies where the routing deviates from the contract drawings
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "Product data — duct materials (metal specification, gauge, coating)"
+ - "Product data — duct sealants, mastics, and tapes"
+ - "Product data — flexible duct (UL 181 listing, R-value)"
+ - "Product data — fire and smoke dampers"
+ - "Product data — duct liner and external insulation"
+ - "Leakage test plan"
+ - "Shop drawings for duct routing and coordination"
+default: "Product data — duct materials (metal specification, gauge, coating)"
+```
+
+## Closeout Submittals {toc}
+
+### At substantial completion and before final acceptance of the duct system, the Contractor shall provide:
+
+- Leakage test reports for all tested duct sections, signed by the testing technician, documenting the test method, instruments (with calibration dates), ambient conditions, measured leakage rates, acceptance criteria, and pass/fail determination; include the corrective action taken and re-test results for any failed section
+- Damper schedule as-built, listing each fire damper and smoke damper by tag number, the fire-rated assembly it serves, the UL listing number, and the access door location
+- Operation and maintenance data for fire dampers, smoke dampers, and motorized control dampers, including manufacturer maintenance intervals and actuator replacement procedures
+- Warranty documentation for ductwork components carrying a manufacturer warranty
+
+```datasheet
+label: Closeout Submittals Required
+type: checkbox
+options:
+ - "Leakage test reports (signed, with calibration dates)"
+ - "Damper schedule as-built"
+ - "Operation and maintenance data for dampers"
+ - "Warranty documentation"
+default: [Leakage test reports (signed, with calibration dates), Damper schedule as-built, Operation and maintenance data for dampers, Warranty documentation]
+```
+
+# Quality Assurance {toc}
+
+## Installer Qualifications {toc}
+
+### Duct fabrication and installation shall be performed by a sheet-metal contractor whose work force consists of trained sheet-metal workers.
+
+### Fabrication of spiral wound and longitudinal seam round duct, flat-oval duct, and rectangular duct shall be performed by personnel experienced in the pressure class and seal class specified.
+
+### Personnel responsible for fire-damper installation shall have received training from the damper manufacturer or a distributor for the specific damper series being installed.
+
+## Regulatory Inspection and Coordination {toc}
+
+### The Contractor shall coordinate the scheduling of inspections of fire damper installations, duct penetrations of rated barriers, and duct liner installations with the Authority Having Jurisdiction before those elements are concealed.
+
+### Fire dampers installed in rated barriers shall not be concealed by ceiling finishes, furring, or access panels until the damper installation has been inspected and released.
+
+### The Contractor shall submit the damper schedule to the AHJ with sufficient lead time to schedule the inspection without delaying construction.
+
+## Source Quality Control {toc}
+
+### Duct materials shall be purchased from suppliers who provide mill certifications confirming conformance to the applicable ASTM material specification.
+
+### Certifications shall be retained by the Contractor for the duration of the project and made available to the Engineer on request.
+
+### Gauge shall not be reduced below the SMACNA HVAC Duct Construction Standards minimum for the declared pressure class under any circumstances, including bid-phase value engineering, without a written change order.
+
+## Mock-Up {toc}
+
+### Where the project involves more than 5,000 ft² of duct cross-sectional area at a single pressure class, or where the Engineer specifies it, the Contractor shall install a mock-up panel of the specified seal class before beginning production work.
+
+### The mock-up shall be of a size sufficient to demonstrate the joint type and sealant application proposed.
+
+### The Engineer shall review the mock-up for conformance with the seal class requirements of this standard before authorizing production installation.
+
+# Environmental and Service Conditions {toc}
+
+## Ductwork must be designed and fabricated for the environmental conditions of its installed location.
+## Metal ductwork in contact with dissimilar metals, in corrosive environments, or exposed to outdoor weather requires material selection and protective measures beyond the standard galvanized steel used in normal interior applications. {note}
+
+## Interior Conditioned or Mechanical Space {toc}
+
+### Standard galvanized steel conforming to ASTM A653, G90 coating designation, is appropriate for normal interior HVAC applications in conditioned or semiconditioned spaces.
+
+### G90 provides a minimum average total-both-sides coating of 0.90 oz/ft² and gives adequate corrosion life in normal building environments. {note}
+
+## Exterior and Outdoor-Air Applications {toc}
+
+### Duct installed outdoors, in partially open parking structures, in outdoor air plenums, or in other locations exposed to weather, driving rain, or sustained high humidity shall use a heavier galvanized coating, aluminum alloy, or stainless steel as specified by the Engineer.
+
+### External insulation and jacketing applied over outdoor duct shall protect the metal from moisture intrusion.
+
+## Corrosive and High-Humidity Applications {toc}
+
+### In indoor swimming pools, natatoriums, chemical storage areas, and other spaces with corrosive or persistently high-humidity conditions, duct material selection shall be approved by the Engineer for the specific environment.
+
+### Standard galvanized steel is not acceptable where chloride concentrations, pool chemical vapors, or persistent condensation would attack the zinc coating.
+
+## Material Selection Datasheet {toc}
+
+```datasheet
+label: Duct Material for this System
+type: radio
+options:
+ - "Galvanized steel, ASTM A653, G90 coating (standard interior)"
+ - "Galvanized steel, ASTM A653, G90 coating, with exterior insulation jacket"
+ - "Aluminum alloy, ASTM B209, 3003-H14 or 5052-H32"
+ - "Stainless steel, ASTM A240, Type 304"
+ - "Stainless steel, ASTM A240, Type 316 (corrosive environments)"
+default: "Galvanized steel, ASTM A653, G90 coating (standard interior)"
+```
+
+### Aluminum shall not be installed in contact with dissimilar metals, cementitious materials, or soil without isolating gaskets or coatings because galvanic attack will rapidly consume the aluminum.
+
+### Stainless steel type 316 shall be used where chloride exposure is anticipated, because chlorides attack the passive film on type 304 and cause pitting.
+
+### Aluminum ductwork offers significant weight reduction compared to galvanized steel and natural corrosion resistance, making it appropriate for outdoor applications and some corrosive environments, and stainless steel type 304 provides resistance to general corrosion. {note}
+
+# Duct Materials {toc}
+
+## Galvanized Steel {toc}
+
+### Galvanized steel duct shall conform to ASTM A653, structural quality, with a hot-dip G90 zinc coating.
+
+### The steel shall be of lock-forming quality, capable of fabrication into duct with seams, joints, and reinforcement attachments without cracking or delamination of the zinc coating.
+
+### G60 coating shall not be substituted for G90 in ductwork.
+
+### G90 coating corresponds to a minimum average zinc deposit of 0.90 oz/ft² total-both-sides. {note}
+
+### Gauge (minimum sheet thickness) for galvanized steel duct shall conform to ANSI/SMACNA 006-2020 for the declared pressure class.
+
+### The Contractor shall verify that the steel purchased meets the minimum thickness specified by SMACNA for each pressure class and duct size, not merely the nominal gauge designation.
+
+### Why minimum thickness governs: the 4th Edition of SMACNA standardized on minimum (not nominal) sheet thickness, because nominal gauge thicknesses vary by supplier and can fall short of the SMACNA minimum; representative gauge ranges by pressure class are shown in the datasheet element below, and the actual SMACNA tables govern. {note}
+
+### Gauge Schedule Datasheet {toc}
+
+```datasheet
+label: Rectangular Duct Gauge Schedule
+type: radio
+options:
+ - "Per SMACNA Table 1-3 for pressure class declared — minimum thickness governs"
+ - "Heavier gauge specified by Engineer — see drawings"
+default: "Per SMACNA Table 1-3 for pressure class declared — minimum thickness governs"
+```
+
+### The Contractor shall use the SMACNA tables for the declared pressure class and shall not reduce gauge by more than one step based on a reinforcement upgrade without verifying that the alternate construction satisfies the SMACNA equivalent construction provisions.
+
+### For rectangular duct, typical galvanized gauge requirements for 2″ w.g. pressure class range from 26 gauge (0.016 in. minimum) for duct up to approximately 30 in. wide to 18 gauge (0.052 in. minimum) for the largest duct sizes, with intermediate gauges for intermediate widths, before accounting for intermediate or major reinforcement; for 4″ w.g. pressure class, gauges are heavier throughout. {note}
+
+## Aluminum {toc}
+
+### Aluminum duct sheet and strip shall conform to ASTM B209, alloy 3003-H14 or 5052-H32.
+
+### Aluminum gauge schedules for the pressure class shall be selected from the SMACNA HVAC Duct Construction Standards tables applicable to aluminum.
+
+### Because aluminum has a lower modulus of elasticity than steel, gauge and reinforcement requirements differ from those for galvanized steel at the same pressure class, which is why the SMACNA aluminum tables are used rather than substituting equivalent steel gauges. {note}
+
+### All aluminum fittings, flanges, reinforcement angles, and attachment hardware in contact with aluminum duct shall be aluminum or stainless steel.
+
+### Steel fasteners shall not be used in aluminum duct assemblies in corrosive or wet environments because the resulting galvanic cell consumes the aluminum.
+
+### Where aluminum duct connects to steel equipment, an isolating transition coupling or gasket shall be provided.
+
+## Stainless Steel {toc}
+
+### Stainless steel duct sheet shall conform to ASTM A240.
+
+### Type 304 is appropriate for most applications where stainless is required.
+
+### Type 316 shall be used where chloride contamination is anticipated.
+
+### Gauge schedules shall conform to SMACNA or shall be calculated by the Engineer for the declared pressure class.
+
+### Stainless steel has higher yield strength than galvanized steel at equivalent gauge, so SMACNA stainless tables reflect reduced gauge requirements relative to steel. {note}
+
+### Welding, if required for stainless steel ductwork, shall be performed by qualified welders using stainless filler metal compatible with the base alloy.
+
+# Pressure and Seal Classifications {toc}
+
+## Pressure Classes {toc}
+
+### Duct pressure class designates the maximum static pressure the duct must withstand and governs gauge, reinforcement, seam type, and seal class selection.
+### SMACNA defines pressure classes of ±0.5, ±1, ±2, ±3, ±4, ±6, and ±10 in. w.g. {note}
+
+### The pressure class shall be established by the mechanical engineer based on the system fan static pressure, the duct routing, and the pressure distribution in the system, and shall be indicated on the contract documents for each duct system or duct zone.
+
+### Where the pressure class is not indicated on the contract documents, the Contractor shall use +1 in. w.g. for low-pressure supply and return systems in accordance with SMACNA.
+
+### Variable-air-volume systems with pressure-independent boxes shall use the pressure class corresponding to the maximum static pressure at the inlet to each duct zone, not the average system pressure.
+
+### Pressure Class Datasheet {toc}
+
+```datasheet
+label: Duct Pressure Class
+type: select
+unit: in. w.g.
+drawing_ref: true
+options:
+ - "±0.5 in. w.g."
+ - "±1 in. w.g."
+ - "±2 in. w.g."
+ - "±3 in. w.g."
+ - "±4 in. w.g."
+ - "±6 in. w.g."
+ - "±10 in. w.g."
+default: "±1 in. w.g."
+```
+
+### The Engineer shall designate pressure zones and indicate the applicable pressure class for each zone on the mechanical drawings.
+
+### A common design error is specifying +1 in. w.g. pressure class throughout a medium-pressure VAV system and relying on SMACNA's "if not stated, use 1 in." default; the 1 in. w.g. pressure class is only appropriate at duct points where the actual static pressure is 1 in. w.g. or less, and where the duct is directly connected to a fan outlet or immediately downstream of a VAV fan that operates at 3–5 in. w.g. total static, the duct immediately adjacent to the fan must be designed for the higher pressure class. {note}
+
+## Seal Classes {toc}
+
+### Seal classes govern which duct surfaces must be sealed and the application method.
+### SMACNA defines three seal classes, with Class A being the most stringent and Class C the least. {note}
+
+### Seal Class A — all transverse joints, all longitudinal seams, and all duct wall penetrations (including wire and control penetrations) shall be sealed.
+
+### Seal Class A is required for pressure class 4 in. w.g. and above, and may also be required at lower pressure classes for energy-efficiency or clean-room projects where indicated on the contract documents.
+
+### Seal Class B — all transverse joints and all longitudinal seams shall be sealed.
+
+### Under Seal Class B penetrations through the duct wall shall be sealed where the system energy standard requires it.
+
+### Seal Class B is required for pressure class 3 in. w.g.
+
+### Seal Class C — transverse joints only shall be sealed.
+
+### Seal Class C is permitted for pressure class 2 in. w.g. and below; where energy codes or project-specific requirements mandate Seal Class B or higher, the Contractor shall apply the more stringent requirement.
+
+### Seal Class Datasheet {toc}
+
+```datasheet
+label: Duct Seal Class
+type: radio
+options:
+ - "Class A — all transverse joints, longitudinal seams, and wall penetrations"
+ - "Class B — all transverse joints and longitudinal seams"
+ - "Class C — transverse joints only"
+default: "Class B — all transverse joints and longitudinal seams"
+```
+
+### The Engineer shall confirm the energy code requirement for the project jurisdiction and designate the minimum seal class accordingly on the contract documents.
+
+### Energy code context for seal class: ASHRAE 90.1 requires that supply and return air ducts in unconditioned spaces, and all ducts in high-pressure systems, be sealed to the level required for the declared pressure class; many jurisdictions adopting ASHRAE 90.1 or IECC effectively mandate Seal Class B for all commercial duct systems regardless of pressure class, and specifying Seal Class B as the project default regardless of pressure class is the conservative and increasingly standard practice for commercial work. {note}
+
+# Duct Construction and Reinforcement {toc}
+
+## Rectangular Duct {toc}
+
+### Rectangular duct shall be fabricated and reinforced in conformance with ANSI/SMACNA 006-2020, Tables 1-3 through 1-11 and the associated construction details, for the declared pressure class.
+
+### The following requirements supplement the SMACNA tables and represent the most frequently encountered field issues. {note}
+
+### Transverse joints shall be of a type listed in SMACNA for the declared pressure class and the duct size.
+
+### Standing drive slip (S-drive), pocket drive slip, and companion angle joints are acceptable at low pressure classes for smaller duct sizes.
+
+### Pittsburgh lock longitudinal seams are the standard for rectangular duct fabricated in the shop.
+
+### Button punch snap lock is permitted for low-pressure duct only and is not acceptable for pressure class 2 in. w.g. and above.
+
+### Grooved seams shall not be used for exterior or outdoor ductwork because moisture intrusion into the seam promotes corrosion.
+
+### Flanged joint systems (TDC/TDF and equivalent roll-formed flanged systems) are acceptable transverse joint methods where listed by SMACNA for the declared pressure class.
+
+### Flanged joint systems used at pressure class 2 in. w.g. and above shall use corner clips and gaskets of the type listed with the joint system, and the Contractor shall follow the manufacturer's installation instructions for bolt torque or clip spacing.
+
+### Omitting corner clips or substituting uncertified generic corner pieces for a listed flanged joint system is not acceptable because it defeats the joint's pressure rating.
+
+### Transverse Joint Datasheet {toc}
+
+```datasheet
+label: Transverse Joint Type — Rectangular Duct
+type: select
+options:
+ - "Flanged joint system (TDC/TDF or equivalent) — listed for pressure class"
+ - "Companion angle flanges, bolted at spacing per SMACNA"
+ - "Standing drive slip and pocket drive slip (low pressure, small duct only)"
+default: "Flanged joint system (TDC/TDF or equivalent) — listed for pressure class"
+```
+
+### Reinforcement spacing and size shall conform to SMACNA for the declared pressure class.
+
+### Intermediate reinforcement (angle iron, hat channel, or equivalent structural shape) shall be sized and spaced per the SMACNA reinforcement tables.
+
+### The spacing intervals in SMACNA are maximum spacings; closer reinforcement spacing is always acceptable. {note}
+
+### Where duct size or pressure class requires major reinforcement (spacing of 2 ft or less at high pressure), the Contractor shall verify that the reinforcement is attached through the duct wall to prevent the duct panel from separating from the reinforcement under pressure.
+
+### Internal tie rods, where required by SMACNA for very large duct dimensions, shall be installed with backing plates at both duct walls to distribute the load and shall not be used as supports for internal elements such as damper blades or turning vanes.
+
+### Duct aspect ratio shall be minimized consistent with the space constraints indicated on the drawings.
+
+### Where layout permits, the Contractor should discuss with the Engineer whether a round or lower-aspect-ratio alternative achieves the required cross-sectional area within the available space.
+
+### High-aspect-ratio rectangular duct (width-to-height ratios above approximately 4:1) requires heavier gauge and closer reinforcement to resist panel deflection, increases friction loss per unit of cross-sectional area, and is more prone to drumming and vibration. {note}
+
+## Round and Spiral Duct {toc}
+
+### Round duct shall be spiral-wound or longitudinal-seam welded in conformance with ANSI/SMACNA 006-2020.
+
+### Gauge for spiral round duct shall conform to SMACNA Table 3-1 for the declared pressure class.
+
+### Spiral-wound duct is the standard fabrication method for round supply and return duct in commercial applications, and round duct gauge requirements are lower than rectangular duct at equivalent size and pressure because the cylindrical form distributes internal pressure in pure hoop tension without bending stress on flat panels, which is the fundamental structural advantage of round duct. {note}
+
+### Fabrication Method Datasheet {toc}
+
+```datasheet
+label: Round Duct Fabrication Method
+type: radio
+options:
+ - "Spiral wound, continuously welded seam"
+ - "Longitudinal seam, welded or lock-formed"
+default: "Spiral wound, continuously welded seam"
+```
+
+### Round fittings shall be fabricated from the same material and at least the same gauge as the connecting straight duct.
+
+### Elbows for round duct shall have a centerline radius of at least 1.0 times the duct diameter (R/D ≥ 1.0) for low-pressure systems.
+
+### Gored elbows are acceptable for sizes 12 in. diameter and above at the pressure class indicated; the number of gores (segments) shall be not less than three for 45-degree elbows and not less than four for 90-degree elbows for diameters 12 in. and below, and five-gore (or more) construction shall be used for larger diameters and high-pressure applications to reduce fitting loss coefficients.
+
+### Tees and wye fittings for round duct shall be conical tees or 45-degree entry wyes rather than square-cut tee intersections.
+
+### Square-cut tap connections create high entry loss and turbulence that significantly reduces branch airflow compared to design values and is one of the most common sources of air-balancing RFIs in round duct systems. {note}
+
+## Flat-Oval Duct {toc}
+
+### Flat-oval duct provides the flow cross-section advantage of round duct with a reduced installation height, making it useful where round duct cannot fit within structural bays but rectangular duct of equivalent area would be too large. {note}
+
+### Flat-oval duct shall be fabricated and reinforced in conformance with ANSI/SMACNA 006-2020, which introduced dedicated flat-oval tables in the 4th Edition for both positive and negative pressure applications.
+
+### Flat-Oval Datasheet {toc}
+
+```datasheet
+label: Flat-Oval Duct
+type: radio
+options:
+ - "Not used on this project"
+ - "Used — fabricate per SMACNA flat-oval tables for declared pressure class"
+default: "Not used on this project"
+```
+
+### Flat-oval fittings shall be fabricated to match the duct and shall conform to SMACNA.
+
+### Transitions from flat-oval to rectangular or round shall be gradual — a total included angle of 30 degrees or less on each side is recommended to avoid flow separation — and shall be shown on shop drawings.
+
+# Fittings {toc}
+
+## General Requirements {toc}
+
+### All fittings, including elbows, tees, wyes, offsets, transitions, and boot connections, shall be fabricated from the same material and at least the same gauge as the adjoining straight duct, at the declared pressure class.
+
+### Fittings fabricated from lighter gauge sheet than the straight duct are a common field substitution and are not acceptable because they create the weakest points in the system at the locations of highest turbulence and dynamic pressure. {note}
+
+## Rectangular Elbows {toc}
+
+### Rectangular elbows shall be square-throat with turning vanes or radius-throat (curved elbows) as indicated on the contract drawings or as selected by the Contractor to meet the available space.
+
+### Square-throat elbows without turning vanes shall not be used in main supply or return ducts.
+
+### Square-throat elbows without turning vanes have a loss coefficient of approximately 1.3 or higher, while square-throat elbows with turning vanes reduce the loss coefficient to approximately 0.10 to 0.20 and are the standard for main duct elbows. {note}
+
+### Turning vanes shall be the double-wall airfoil type for all elbows in medium-pressure and high-pressure systems (pressure class 2 in. w.g. and above).
+
+### Single-thickness vanes are acceptable in low-pressure systems for duct widths up to 36 in.
+
+### Turning vanes shall be mounted in rails and shall be secured so that they cannot come loose under operating pressures.
+
+### Turning vane spacing shall conform to SMACNA.
+
+### Vane gauge shall be not less than 26 gauge for 2 in. vanes and not less than 24 gauge for 4 in. vanes, in conformance with SMACNA.
+
+### Radius elbows shall have a centerline radius of at least 1.0 times the duct width (R/W ≥ 1.0) measured in the plane of the turn.
+
+### The use of R/W < 0.75 shall not be used except where specifically approved by the Engineer.
+
+### The use of R/W < 0.75 creates significant flow separation on the inside of the elbow that persists for 10 to 15 duct diameters downstream. {note}
+
+### Elbow Type Datasheet {toc}
+
+```datasheet
+label: Rectangular Duct Elbow Type
+type: radio
+options:
+ - "Square throat with double-wall airfoil turning vanes (medium/high pressure)"
+ - "Square throat with single-wall turning vanes (low pressure, W ≤ 36 in.)"
+ - "Radius elbow, R/W ≥ 1.0"
+ - "Radius elbow, R/W ≥ 1.5 (low loss, shown on drawings)"
+default: "Square throat with double-wall airfoil turning vanes (medium/high pressure)"
+```
+
+## Transitions {toc}
+
+### Transitions that change duct size shall have a total included angle not exceeding 30 degrees on each side for diverging (expansion) transitions to prevent flow separation.
+
+### Converging (contraction) transitions are less sensitive to angle.
+
+### Where space constraints require a transition angle greater than 30 degrees, turning vanes or a splitter may be required; the Contractor shall note on the shop drawing when a transition exceeds this guideline and obtain Engineer review.
+
+## Offsets and Conical Tee Connections {toc}
+
+### Offsets shall be fabricated as two-piece or three-piece fittings to maintain reasonable transition angles.
+
+### Connections from round main ducts to round branches shall use conical or saddle taps rather than raw hole taps.
+
+### The high loss and turbulence of a raw hole tap (a drilled hole with no conical entry fitting) frequently causes branch-circuit air quantities to be significantly below design values and is one of the leading sources of TAB RFIs. {note}
+
+# Flexible Duct {toc}
+
+## Listing and Classification {toc}
+
+### Flexible duct shall be factory-made, listed to UL 181 as a Class 1 air duct.
+
+### Class 1 requires a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 when tested in accordance with ASTM E84. {note}
+
+### Flexible air connectors (limited to 14 ft by UL listing) are not equivalent to flexible air ducts and shall not be used as a substitute where flexible duct is required.
+
+### Listing Datasheet {toc}
+
+```datasheet
+label: Flexible Duct UL 181 Listing Required
+type: radio
+options:
+ - "Yes — UL 181, Class 1 air duct listing required"
+ - "Not applicable — no flexible duct on this project"
+default: "Yes — UL 181, Class 1 air duct listing required"
+```
+
+## Maximum Length {toc}
+
+### Flexible duct runs shall be as short as practicable.
+
+### The maximum allowable length of any single flexible duct run shall not exceed 6 ft, measured along the duct centerline in the installed position, except where the contract documents specifically permit longer runs for a defined purpose.
+
+### Longer flexible duct runs increase resistance disproportionately relative to rigid duct, particularly when the duct is not fully extended, and create airflow deficiencies at the served outlets; long runs of flex duct used in place of rigid duct to avoid coordination problems are a frequent source of complaints from building owners and are not acceptable. {note}
+
+### Maximum Length Datasheet {toc}
+
+```datasheet
+label: Maximum Flexible Duct Run Length
+type: range
+unit: ft
+options:
+ min: 2
+ max: 14
+ setpoints: [2, 4, 6, 8, 10, 14]
+default: 6
+```
+
+## Extension and Sag {toc}
+
+### Flexible duct shall be installed fully extended, with the inner core pulled taut and without excess length coiled or looped in the ceiling.
+
+### The installed duct shall not be compressed or convoluted.
+
+### Sag between supports shall not exceed 1/2 in. per foot of horizontal run.
+
+### Excess length increases friction loss approximately as the square of the length ratio and is the single most common installation defect in flexible duct systems. {note}
+
+## Bends and Turns {toc}
+
+### Bends in flexible duct shall have a centerline bend radius of at least 1.0 times the duct diameter.
+
+### The flex duct shall be allowed to run straight for a minimum of 12 in. from any plenum, collar, or rigid duct connection before making a bend, to allow the flow to develop before the direction change.
+
+### Tight bends immediately at the collar connection shall not be permitted.
+
+### Tight bends immediately at the collar connection are a leading cause of poor airflow to diffusers. {note}
+
+## Support and Hanger Spacing {toc}
+
+### Flexible duct shall be supported at intervals not exceeding 4 ft on horizontal runs in conformance with ANSI/SMACNA 006-2020, Fourth Edition.
+
+### Support straps or hangers shall be at least 1.5 in. wide and shall not constrict the inner core.
+
+### Pinching or cinching the support strap tight enough to reduce the internal diameter is not acceptable.
+
+### Flexible duct shall not sag more than 1/2 in. per foot of unsupported span.
+
+### Hanger Spacing Datasheet {toc}
+
+```datasheet
+label: Flexible Duct Hanger Maximum Spacing
+type: range
+unit: ft
+options:
+ min: 2
+ max: 4
+ setpoints: [2, 3, 4]
+default: 4
+```
+
+## Connections {toc}
+
+### Flexible duct connections to rigid duct, air terminal units, and air distribution devices shall be made using sheet-metal collars, sleeves, or flexible connections designed for the purpose.
+
+### The inner core jacket shall extend over the collar a minimum of 1.5 in. and shall be secured with a draw band (worm-gear clamp).
+
+### The outer insulation jacket and vapor barrier shall then be drawn over the connection, overlapping the collar by at least 2 in., and secured with a second draw band.
+
+### The connection shall be sealed with UL 181B listed tape or mastic.
+
+### Connections made with duct tape (pressure-sensitive cloth-backed tape) are not acceptable for any application.
+
+### Cloth-backed duct tape is not UL 181B listed and degrades and fails within a few years of installation. {note}
+
+# Duct Insulation and Liner {toc}
+
+## Duct Liner {toc}
+
+### Duct liner is applied to the interior surface of the duct and provides both thermal insulation and sound attenuation. {note}
+### The primary acoustical benefit of liner is the reduction of fan and system-generated noise transmitted through the duct walls. {note}
+
+### Duct liner shall conform to ASTM C1071 and shall have a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 per ASTM E84 when tested as an assembly.
+
+### The liner face velocity shall not exceed the liner manufacturer's maximum recommended face velocity.
+
+### The Engineer shall specify a lower limit or a different liner material where system velocities exceed the standard face velocity limit.
+
+### Exceeding face velocity limits can cause liner fibers to erode and enter the airstream, which represents an indoor air quality concern; the standard face velocity limit for most fibrous glass liners is 6,000 ft/min. {note}
+
+### Liner shall not be installed in supply duct downstream of humidifiers or in portions of the system subject to persistent moisture accumulation (condensation zones, kitchen exhaust, etc.) because moisture degrades fibrous glass liner over time and promotes microbial growth.
+
+### In moisture-prone zones, smooth-interior unlined duct with external insulation is preferred.
+
+### Duct Liner Datasheet {toc}
+
+```datasheet
+label: Duct Liner
+type: radio
+options:
+ - "Not used — external insulation only"
+ - "Provided — ASTM C1071, 1 in. thick (R-4 nominal)"
+ - "Provided — ASTM C1071, 1.5 in. thick (R-6 nominal)"
+ - "Provided — ASTM C1071, 2 in. thick (R-8 nominal)"
+default: "Not used — external insulation only"
+```
+
+### Liner shall be adhered continuously to the duct interior surface with a water-resistant adhesive, and mechanical fasteners (stick pins with clips or weld pins) shall be installed at a spacing not exceeding 18 in. in each direction to prevent the liner from separating from the duct wall.
+
+### All liner edges at duct openings, elbows, and access doors shall be coated or sealed to prevent erosion of the exposed edge into the airstream.
+
+### Impaled-pin fastener caps shall be the same material as the liner facing.
+
+### Liner thickness shall be as shown on the contract documents; where not shown, a minimum of 1 in. thick liner shall be provided.
+
+### The duct shall be fabricated oversize to maintain the design airflow area, so that the specified duct dimension is the clear inside dimension after liner installation.
+
+### Fabricating duct to the design dimension and then applying liner inside reduces the cross-sectional area and increases velocity beyond design values, and is not acceptable. {note}
+
+## External Duct Insulation {toc}
+
+### External duct insulation (duct wrap) shall be applied to ducts in unconditioned spaces, in semi-conditioned spaces, in ceiling plenums not serving as return air plenums, and in all locations outside the conditioned envelope, in conformance with ASHRAE 90.1 for the applicable climate zone and duct location.
+
+### R-Value Datasheets {toc}
+
+```datasheet
+label: External Duct Insulation R-Value — Ducts in Unconditioned Spaces
+type: select
+unit: h·ft²·°F/Btu
+drawing_ref: true
+options:
+ - "R-4.2"
+ - "R-6"
+ - "R-8"
+ - "R-12"
+default: "R-6"
+```
+
+```datasheet
+label: External Duct Insulation R-Value — Ducts Outdoors or in Ventilated Attics
+type: select
+unit: h·ft²·°F/Btu
+drawing_ref: true
+options:
+ - "R-6"
+ - "R-8"
+ - "R-12"
+default: "R-8"
+```
+
+### The Engineer shall specify the required R-value by location on the contract documents based on the project climate zone.
+
+### ASHRAE 90.1 R-value context: ASHRAE 90.1 (current edition) establishes minimum R-values for ducts by location and climate zone — for Climate Zones 1 through 3, R-6 is a common minimum for unconditioned space ducts, and for Climate Zones 4 and above, R-8 is often required for unconditioned spaces and R-12 for outdoor ducts; the above defaults are representative for Climate Zone 3B/4A and are to be verified for the specific project. {note}
+
+### External duct insulation shall conform to ASTM C553 (mineral fiber blanket) or other approved material.
+
+### Insulation shall have a factory-applied vapor retarder jacket for supply air duct systems carrying conditioned air in unconditioned spaces.
+
+### The vapor retarder shall have a permeance of 0.10 perm or less (Class II vapor retarder).
+
+### Joints in the vapor retarder shall be sealed with tape compatible with the jacket material to maintain a continuous vapor barrier.
+
+### Incomplete or punctured vapor retarders on cold-air supply ducts in humid unconditioned spaces will result in condensation, dripping, and over time insulation deterioration and microbial growth. {note}
+
+### Installed insulation thickness to achieve the specified R-value shall account for the compression factor, so that the selected product nominal thickness provides the required R-value at installed thickness, not at nominal thickness.
+
+### For flexible duct wrap installed on rectangular duct, the installed thickness is approximately 75 percent of nominal thickness due to compression at corners and supports. {note}
+
+### Vapor Retarder Datasheet {toc}
+
+```datasheet
+label: External Insulation Vapor Retarder Jacket
+type: radio
+options:
+ - "Factory-applied FSK (foil-scrim-kraft) jacket, ≤ 0.10 perm"
+ - "Factory-applied reinforced aluminum foil jacket, ≤ 0.10 perm"
+ - "Not required — duct in conditioned space"
+default: "Factory-applied FSK (foil-scrim-kraft) jacket, ≤ 0.10 perm"
+```
+
+# Duct Sealants {toc}
+
+## General Sealant Requirements {toc}
+
+### All duct sealing materials shall be compatible with the duct material and shall remain effective at the operating temperature and pressure of the system.
+
+### Sealants shall be applied to clean, dry, dust-free surfaces.
+
+### Applying sealant to dusty, oily, or damp duct surfaces prevents adhesion and causes early sealant failure, which is a leading cause of duct leakage test failures on projects where sealant was applied but not to clean surfaces. {note}
+
+## Mastic Sealant {toc}
+
+### Water-based mastic is the preferred sealant for transverse joints, longitudinal seams, and duct wall penetrations in metal ductwork.
+
+### Mastic shall conform to UL 181A-M for application to rigid ducts.
+
+### Mastic shall be applied in a continuous bead and tooled to fill the joint completely, with the excess feathered onto the adjacent duct surface.
+
+### The dry-film thickness shall conform to the manufacturer's recommendation.
+
+### A single thin coat is not sufficient to fill gaps at flanged joints. {note}
+
+### Where gaps exceed 1/4 in. at any joint, mastic alone is insufficient and the gap shall be bridged by applying fiberglass mesh tape before applying mastic.
+
+### The mastic shall be worked through the mesh fabric and shall fully embed the fabric.
+
+### Joints with gaps exceeding 3/4 in. shall be re-fabricated or re-fitted, not merely bridged with mesh and mastic.
+
+### Large gaps that cannot be closed by mesh-reinforced mastic indicate a fabrication defect. {note}
+
+### Primary Sealant Datasheet {toc}
+
+```datasheet
+label: Primary Sealant Type — Metal Ductwork
+type: radio
+options:
+ - "Water-based mastic, UL 181A-M listed"
+ - "Spray-applied duct sealant, UL 181A-M listed (shop application)"
+ - "Aerosolized sealant injected into installed duct (remedial use only)"
+default: "Water-based mastic, UL 181A-M listed"
+```
+
+## Foil Tape {toc}
+
+### Pressure-sensitive foil tape, listed to UL 181A-P, is acceptable as a supplement to mastic but shall not be used as the sole sealant at transverse joints in ducts at pressure class 2 in. w.g. and above.
+
+### Foil tape is appropriate for sealing longitudinal seams on spiral round duct and for patching small punctures.
+
+### Cloth-backed duct tape is not UL 181A or 181A-P listed and is not acceptable for ductwork sealing in any application.
+
+## Flexible Duct Connections {toc}
+
+### Sealants and tapes for flexible duct connections shall be listed to UL 181B-M or UL 181B-FX, respectively, conforming to the applicable closure class.
+
+### Connections at flexible duct collars shall use draw bands and UL 181B listed tape or mastic as described in the flexible duct section.
+
+# Accessories {toc}
+
+## Fire Dampers {toc}
+
+### Fire dampers shall be installed in ductwork where ducts penetrate or terminate at openings in fire-rated assemblies (walls, floors, and partitions) required to have a fire-resistance rating of 2 hours or more, in accordance with NFPA 90A and the IMC.
+
+### Fire dampers shall be listed to UL 555, suitable for dynamic or static duty as required by the installation condition.
+
+### Where the fan serves the duct without an upstream isolation point, dynamic-rated dampers (rated while the air system is running) shall be used; static dampers may only be used where the fire-safety system shuts down the fan before the damper closes.
+
+### Fire dampers shall be rated for a minimum of 1.5 hours or 3 hours as required by the fire-resistance rating of the assembly being penetrated, in conformance with the building code.
+
+### The Contractor shall verify the required rating for each damper location from the fire-rated assembly schedule on the architectural drawings.
+
+### Fire Damper Datasheets {toc}
+
+```datasheet
+label: Fire Damper Rating
+type: radio
+options:
+ - "1.5 hours (for assemblies requiring 2-hour rating per IBC/IMC)"
+ - "3 hours (for assemblies requiring 3-hour or greater rating)"
+default: "1.5 hours (for assemblies requiring 2-hour rating per IBC/IMC)"
+```
+
+```datasheet
+label: Fire Damper Duty Rating
+type: radio
+options:
+ - "Dynamic (fan operates until damper closes — standard for VAV systems)"
+ - "Static (fan shut down before damper closes)"
+default: "Dynamic (fan operates until damper closes — standard for VAV systems)"
+```
+
+### Fire dampers shall be installed in the plane of the rated assembly in conformance with their UL listing and the manufacturer's installation instructions.
+
+### The damper shall be installed using a sleeve transition or breakaway connection so that thermal expansion of the duct does not impose loads on the rated assembly.
+
+### Retaining angles or frames shall be provided in conformance with UL 555 listing requirements to prevent the damper from being displaced when the duct collapses under fire conditions.
+
+### Each fire damper shall be equipped with an access door located immediately adjacent to the damper on the side that provides access to the fusible link or actuator and the reset mechanism.
+
+### Access door size shall be not less than 16 in. × 16 in., or not less than 18 in. in diameter for round duct, sufficient to allow inspection, link replacement, and damper reset without removing building finishes.
+
+### Access panels in fire-rated assemblies shall be rated to match the assembly.
+
+## Smoke Dampers {toc}
+
+### Smoke dampers shall be listed to UL 555S and shall be installed where required by NFPA 90A, the IMC, and the building fire protection and life safety design.
+
+### Smoke dampers shall be installed in ductwork at penetrations of smoke barriers and in HVAC systems with a capacity exceeding 15,000 cfm to isolate the air-handling equipment from the duct distribution system in a smoke-control event.
+
+### Smoke dampers shall be equipped with a suitable actuator — electric or pneumatic — capable of closing within the time required by the system smoke-control sequence, and shall be supervised by the fire alarm system in conformance with the Life Safety Contractor's requirements.
+
+### Smoke dampers shall be capable of holding closed against the maximum system pressure and of operating over the full temperature range of the installation.
+
+### Smoke Damper Actuator Datasheet {toc}
+
+```datasheet
+label: Smoke Damper Actuator Type
+type: radio
+options:
+ - "Electric, 24 VAC, spring return fail-closed"
+ - "Electric, 120 VAC, spring return fail-closed"
+ - "Pneumatic, fail-closed"
+default: "Electric, 24 VAC, spring return fail-closed"
+```
+
+### Each smoke damper shall be provided with an access door on each side of the assembly it penetrates (or on the side with the actuator) that complies with NFPA 90A access requirements.
+
+### Access to smoke dampers shall not require removal of permanent construction.
+
+### The fire alarm contractor shall coordinate actuator wiring and supervisory connections with the HVAC Contractor.
+
+### The HVAC Contractor is responsible for installing the damper and the access door and for providing the rough-in provisions required by the actuator manufacturer.
+
+## Combination Fire and Smoke Dampers {toc}
+
+### Where both a fire rating and smoke control are required at a single penetration, a combination fire/smoke damper listed to both UL 555 and UL 555S shall be installed.
+
+### Combination dampers shall comply with the requirements of both this section and the fire damper and smoke damper sections above.
+
+## Volume Control Dampers {toc}
+
+### Volume control dampers (manual balancing dampers) shall be installed in branch ducts at locations shown on the contract drawings to allow balancing of airflow.
+
+### Volume control dampers shall be opposed-blade (for control applications) or single-blade (for zone shutoff) type as shown on the contract drawings.
+
+### Dampers shall be equipped with quadrant handles with locking nuts that maintain the set position permanently after balancing.
+
+### The Contractor shall provide all volume control dampers at the locations shown on the drawings and shall not omit dampers as a cost-reduction measure.
+
+### Missing volume control dampers prevent the TAB contractor from balancing the system and are a frequent source of punch-list items. {note}
+
+### Volume Control Damper Datasheet {toc}
+
+```datasheet
+label: Volume Control Damper Blade Type
+type: radio
+options:
+ - "Opposed blade (for throttling and control)"
+ - "Single blade / butterfly (for zone shut-off)"
+default: "Opposed blade (for throttling and control)"
+```
+
+## Access Doors in Ductwork {toc}
+
+### Access doors shall be provided in the duct at locations indicated on the contract documents and at every fire damper, smoke damper, combination fire/smoke damper, and flow-measuring station.
+
+### Access doors shall also be provided at coil access points, filter frames, and other components requiring maintenance access through the duct wall.
+
+### Access doors shall be airtight, shall be hinged or removable, and shall be constructed of the same material and at least the same gauge as the duct they serve.
+
+### For pressure class 2 in. w.g. and above, access doors shall incorporate a gasket around the perimeter to prevent leakage.
+
+### Access door frames shall be sealed to the duct with mastic before installation.
+
+### Access door size shall be not less than 12 in. × 12 in. for ducts up to 24 in. in the smaller dimension, and shall be not less than 18 in. × 18 in. for larger ducts to permit personnel to work inside.
+
+### Access door size shall in all cases be sufficient to inspect, test, and reset the device served.
+
+### Access Door Datasheet {toc}
+
+```datasheet
+label: Access Door Minimum Size
+type: radio
+unit: in
+options:
+ - "12 × 12 (ducts ≤ 24 in. smaller dimension)"
+ - "18 × 18 (ducts > 24 in. smaller dimension)"
+ - "As shown on drawings (custom size for specific access requirement)"
+default: "12 × 12 (ducts ≤ 24 in. smaller dimension)"
+```
+
+# Hangers and Supports {toc}
+
+## General Support Requirements {toc}
+
+### Ductwork shall be supported from the building structure — concrete structure, steel framing, or wood framing — using hangers, trapeze supports, or wall brackets designed and installed for the weight of the duct, the insulation, and any devices mounted on or in the duct.
+
+### Supports shall not be attached to piping, conduit, or other mechanical and electrical systems that are themselves supported from structure.
+
+### Cross-supporting between different systems creates loads on systems not designed for them and is not permitted. {note}
+
+### Support spacing, rod diameter, and trapeze member size shall conform to SMACNA HVAC Duct Construction Standards, Tables 4-1 through 4-4, for the duct size and pressure class.
+
+### The SMACNA hanger tables provide maximum spacing and minimum rod/strap sizes, and closer hanger spacing is always acceptable, often warranted at elbows, transitions, and heavy accessories. {note}
+
+### Hanger Spacing Datasheets {toc}
+
+```datasheet
+label: Maximum Hanger Spacing — Rectangular Duct
+type: range
+unit: ft
+options:
+ min: 4
+ max: 10
+ setpoints: [4, 5, 8, 10]
+default: 8
+```
+
+```datasheet
+label: Maximum Hanger Spacing — Round and Flat-Oval Duct
+type: range
+unit: ft
+options:
+ min: 8
+ max: 12
+ setpoints: [8, 10, 12]
+default: 10
+```
+
+### Additional supports shall be provided within 2 ft of each elbow, transition, and duct intersection, and within 2 ft of each end of flexible duct runs, in conformance with SMACNA.
+
+### Ductwork shall not be supported by the suspended ceiling system; the duct weight shall be carried directly to structure by independent hangers.
+
+## Hanger Types {toc}
+
+### Trapeze hangers shall be used for rectangular duct wider than 42 in. and for duct carrying heavy accessories such as dampers, coil sections, or fan-powered boxes.
+
+### Trapeze lower members shall be steel angle or strut channel of sufficient size to span the duct width without excessive deflection.
+
+### Upper rod sizes for trapeze hangers shall be selected from SMACNA Table 4-2.
+
+### Strap hangers (galvanized steel flat strap) shall be acceptable for rectangular duct up to 42 in. wide where the duct is supported directly from structure without a long rod, and for round and oval duct.
+
+### Strap width and gauge shall conform to SMACNA.
+
+### Hanger rods shall be galvanized steel threaded rod, with nuts and lock washers at all connection points.
+
+### Hanger rods shall be attached to the building structure by means appropriate to the structural material — concrete anchors for concrete, drilled and bolted connections for steel framing, or wood screws for wood framing.
+
+### Power-actuated fasteners shall not be used to attach duct hangers to structural members without Engineer approval.
+
+### Hanger Type Datasheet {toc}
+
+```datasheet
+label: Hanger Type — Rectangular Duct
+type: radio
+options:
+ - "Trapeze (lower angle with upper rods) — ducts over 42 in. wide"
+ - "Flat strap (galvanized) — ducts ≤ 42 in. wide"
+ - "Fabricated bracket — wall-mounted duct"
+default: "Trapeze (lower angle with upper rods) — ducts over 42 in. wide"
+```
+
+## Seismic Bracing {toc}
+
+### Where the project is located in a seismic design category (SDC) requiring seismic restraint of mechanical systems, ductwork shall be laterally braced in conformance with SMACNA Seismic Restraint Manual — Guidelines for Mechanical Systems and the requirements of the adopted building code.
+
+### Seismic bracing shall be designed by a licensed structural or mechanical engineer where required by the local jurisdiction.
+
+### The Contractor shall not omit seismic bracing to reduce cost without a written change in scope.
+
+### SDC B and higher typically requires lateral restraint of ducts larger than specified threshold sizes. {note}
+
+### Seismic Bracing Datasheet {toc}
+
+```datasheet
+label: Seismic Bracing Required
+type: radio
+options:
+ - "Yes — per SMACNA Seismic Restraint Manual and local code"
+ - "No — project SDC does not require duct bracing"
+default: "Yes — per SMACNA Seismic Restraint Manual and local code"
+```
+
+## Vibration Isolation at Equipment Connections {toc}
+
+### Flexible connections shall be provided between ductwork and air-handling units, fans, fan coil units, and other rotating equipment to prevent transmission of vibration and noise into the duct system.
+
+### Flexible connections shall be of neoprene or canvas reinforced fabric, not less than 3 in. long, and shall be installed without tension or compression in the neutral position with the equipment operating.
+
+### The ductwork immediately adjacent to the air-handling unit shall be independently supported so that the weight of the duct does not bear on the flexible connection or on the equipment casing.
+
+### Flexible Connection Datasheet {toc}
+
+```datasheet
+label: Flexible Connections at Equipment
+type: radio
+options:
+ - "Neoprene-coated woven glass fiber fabric, 3 in. minimum length"
+ - "Canvas duck fabric (not for outdoor use), 3 in. minimum length"
+default: "Neoprene-coated woven glass fiber fabric, 3 in. minimum length"
+```
+
+# Installation {toc}
+
+## Coordination and Sequencing {toc}
+
+### Before fabricating shop ductwork, the Contractor shall verify that the routing shown on the contract drawings is achievable within the structure, existing utilities, and other mechanical and electrical systems.
+
+### Where interferences exist, the Contractor shall participate in the BIM coordination process or manual coordination process established for the project and shall resolve interferences before fabrication.
+
+### Field modifications to duct routing made after fabrication to avoid interferences result in non-standard fittings, increased field labor, and delays; early coordination prevents these problems. {note}
+
+## Clearances {toc}
+
+### Ductwork shall be installed with clearances conforming to the IMC.
+
+### Clearances from combustible construction shall be maintained as required by NFPA 90A.
+
+### Where insulated ductwork is installed adjacent to combustible construction, the clearance shall be measured to the outer face of the insulation.
+
+### Where uninsulated metal ductwork is installed near combustible materials, the NFPA 90A minimum clearances shall be maintained.
+
+### The Contractor shall maintain a minimum 1-in. clearance between insulated ductwork and any other building system (piping, conduit, structure) to avoid compression of duct insulation and to allow future maintenance access.
+
+### Duct-to-duct clearances shall allow for insulation installation and maintenance access to dampers and other devices.
+
+## Hangers — Installation Details {toc}
+
+### All threaded rod connections shall be made up wrench-tight with jam nuts to prevent vibration-induced loosening over time.
+
+### Nuts shall be installed above and below the trapeze lower member to prevent the lower member from sliding.
+
+### Duct straps shall be attached to the duct sides, not the bottom, for rectangular duct, to prevent the strap from cutting into the duct bottom under load.
+
+### Round duct strap hangers shall be wide enough to distribute load without deforming the duct cylinder.
+
+## Sealant Application {toc}
+
+### Sealant shall be applied in conformance with this standard and the sealant manufacturer's published application instructions.
+
+### All surfaces to be sealed shall be cleaned of dirt, oil, and loose metal burrs before sealant application.
+
+### Sealant shall be applied before the duct is insulated; sealing over installed insulation is not acceptable.
+
+### For flanged (TDC/TDF) transverse joints, mastic shall be applied to the interior face of both flanges before assembly, and a bead shall be applied to the exterior face of the assembled joint.
+
+### Corner clips and any visible gaps shall be masked with mastic.
+
+### The common practice of applying mastic only to the exterior of an already-assembled flanged joint without interior sealant is not acceptable for Seal Class B or Class A systems; it does not seal the contact face between the flanges.
+
+### For Pittsburgh lock longitudinal seams, mastic shall be applied continuously to the exterior of the seam.
+
+### For spiral round duct, the field joints (slip-and-drive or flanged) shall be sealed with UL 181A listed tape or mastic, while the spiral seam is welded in manufacture and does not require additional field sealing.
+
+## Duct Liner Installation {toc}
+
+### Liner shall be installed per the liner manufacturer's instructions and SMACNA HVAC Duct Construction Standards duct liner details.
+
+### Adhesive shall be applied to 100 percent of the liner surface for duct surfaces facing the airstream, with particular care at corners.
+
+### Mechanical fasteners shall be installed through the liner into the duct wall with caps that prevent the liner from pulling free of the fastener.
+
+### At fittings, liner shall be mitered and fitted to maintain a smooth interior surface.
+
+### Gaps in liner at elbow throats and heels allow airstream exposure of raw liner edges that erode and delaminate over time. {note}
+
+## Fire Damper Installation {toc}
+
+### Fire dampers shall be installed in strict conformance with the UL listing requirements for the specific damper series, the damper manufacturer's installation instructions, and NFPA 90A.
+
+### No installation method, orientation, or accessory configuration that deviates from the listing is acceptable without a specific listing expansion or special engineering approval from the AHJ.
+
+### The Contractor shall coordinate with the structural and architectural trades to ensure that the rated assembly framing is in place before the damper sleeve is installed, that the sleeve is installed plumb and square in the rated assembly, and that the fire-stopping of the annular space between the sleeve and the assembly is completed after damper installation.
+
+### Fire damper locations shall be marked on the as-built drawings with damper tag numbers corresponding to the damper schedule.
+
+### Fusible links in fire dampers shall not be installed until after the duct system construction, cleaning, and leakage testing are complete.
+
+### Installing fusible links during construction exposes them to heat, paint overspray, and mechanical damage and is a common cause of damper failures during commissioning. {note}
+
+## Cleanliness {toc}
+
+### The interior of duct systems shall be protected from contamination during construction.
+
+### Duct openings left in place during construction shall be sealed with cardboard, plastic sheeting, or sheet-metal caps to prevent construction debris — concrete dust, drywall dust, masonry debris, insulation fibers — from entering the duct.
+
+### Duct protection is a routine construction requirement, not an optional quality measure; ducts contaminated with construction debris require costly post-construction cleaning and can cause fan damage when the system is first operated. {note}
+
+### The Contractor shall inspect ductwork before insulation is applied and before access doors are closed and shall remove all debris, tools, and foreign objects.
+
+### Where the owner requires post-construction duct cleaning per NADCA standards, the cleaning contractor's work is a separate scope, and this standard governs the Contractor's obligation to keep the duct clean during construction. {note}
+
+# Leakage Testing {toc}
+
+## Purpose and Scope {toc}
+
+### Leakage testing verifies that the duct system meets the seal class specified and, where the energy code requires it, meets the maximum leakage rate allowed under ASHRAE 90.1.
+
+### Testing shall be conducted in conformance with ANSI/SMACNA 016-2012, HVAC Air Duct Leakage Test Manual, Second Edition.
+
+### Leakage testing shall be performed before duct systems are insulated, before access doors are permanently closed, and before ceilings are installed or duct is otherwise made inaccessible.
+
+### Performing leakage testing after insulation installation reduces the ability to locate and seal leaks when the test fails, and is not acceptable. {note}
+
+### Leakage Testing Datasheet {toc}
+
+```datasheet
+label: Leakage Testing Required
+type: radio
+options:
+ - "Yes — required for all pressure class 2 in. w.g. and above systems"
+ - "Yes — required for all duct systems (including low-pressure) per energy code"
+ - "No — project conditions exempt (confirm with Engineer)"
+default: "Yes — required for all pressure class 2 in. w.g. and above systems"
+```
+
+## Test Sections {toc}
+
+### Testing shall be performed on sections of the duct system totaling a minimum of 25 percent of the total duct surface area, selected to include the sections most likely to leak — high-pressure zones, sections with many joints, and sections near fan connections.
+
+### Where a project-specific energy code requires testing of a larger percentage, the larger percentage governs.
+
+### The leakage test plan submitted by the Contractor shall identify the test sections and the rationale for selection before testing begins.
+
+## Test Method {toc}
+
+### The duct section to be tested shall be isolated by sealing open ends (diffuser and grille openings, flanged connections not yet made, branch openings) with temporary caps or blank-off plates.
+
+### The test fan and flowmeter shall be connected to the isolated section.
+
+### The section shall be pressurized to the test pressure (equal to the declared pressure class for the duct system) and the leakage flow rate shall be measured in cfm using a calibrated flowmeter.
+
+### Test equipment shall be calibrated, and the Contractor shall provide documentation of the calibration date for the flowmeter and pressure gauges used in the test.
+
+### Calibration shall be current within one year or within the instrument manufacturer's recommended calibration interval, whichever is shorter.
+
+## Acceptance Criteria {toc}
+
+### Maximum permitted leakage (Lmax) shall be calculated per the SMACNA leakage test manual formula:
+
+### **Lmax = CL × P^0.65** {note}
+
+### Where: Lmax is the maximum leakage rate in cfm per 100 ft² of duct surface area; CL is the duct leakage class; and P is the test pressure in inches water column equal to the declared pressure class. {note}
+
+### The duct leakage class (CL) values from ANSI/SMACNA 016-2012 (Second Edition) for the declared seal class are: {note}
+
+| Seal Class | CL — Rectangular | CL — Round and Flat-Oval |
+|------------|-------------------|--------------------------|
+| Class A | 4 cfm/100 ft² at 1 in. w.g. | 2 cfm/100 ft² at 1 in. w.g. |
+| Class B | 8 cfm/100 ft² at 1 in. w.g. | 4 cfm/100 ft² at 1 in. w.g. |
+| Class C | 16 cfm/100 ft² at 1 in. w.g. | 8 cfm/100 ft² at 1 in. w.g. |
+
+### Maximum permitted leakage shall be calculated using the formula Lmax = CL × P^0.65 with the CL value for the declared seal class.
+
+### Leakage Class Datasheets {toc}
+
+```datasheet
+label: Maximum Leakage Class (CL) — Rectangular Duct
+type: select
+unit: cfm/100 ft² at 1 in. w.g.
+options:
+ - "CL = 4 (Seal Class A)"
+ - "CL = 8 (Seal Class B)"
+ - "CL = 16 (Seal Class C)"
+default: "CL = 8 (Seal Class B)"
+```
+
+```datasheet
+label: Maximum Leakage Class (CL) — Round and Flat-Oval Duct
+type: select
+unit: cfm/100 ft² at 1 in. w.g.
+options:
+ - "CL = 2 (Seal Class A)"
+ - "CL = 4 (Seal Class B)"
+ - "CL = 8 (Seal Class C)"
+default: "CL = 4 (Seal Class B)"
+```
+
+### Where ASHRAE 90.1 or the energy code imposes a maximum total system leakage expressed as a percentage of total supply airflow or as a fixed cfm/ft² value, the Engineer shall convert that requirement to a CL-equivalent and specify the more stringent of the SMACNA CL or the energy code limit on the contract documents.
+
+## Remediation and Re-Test {toc}
+
+### Where a test section fails to meet the acceptance criterion, the Contractor shall locate the leaks by listening, feeling with a gloved hand, or using a soap solution or smoke pencil while the section is under pressure.
+
+### All identified leaks shall be sealed with mastic or tape per this standard.
+
+### After remediation, the section shall be re-tested to confirm that the corrected leakage is within the acceptance criterion.
+
+### Re-testing shall be performed before insulation is applied to the repaired area.
+
+### Leak Location Datasheet {toc}
+
+```datasheet
+label: Leak Location Method
+type: radio
+options:
+ - "Manual (listening and touch while pressurized)"
+ - "Soap solution or smoke pencil while pressurized"
+ - "Ultrasonic leak detector"
+default: "Soap solution or smoke pencil while pressurized"
+```
+
+## Test Reporting {toc}
+
+### The testing technician shall prepare a written test report for each tested section documenting the section location and tag, the duct surface area of the section, the test pressure, the measured leakage flow rate, the calculated Lmax, the pass/fail determination, the leaks found and corrective action taken, and the post-correction re-test result.
+
+### Reports shall be signed by the testing technician and included in the closeout submittal.
+
+# Delivery, Storage, and Handling {toc}
+
+## Shop-fabricated ductwork shall be protected during transportation to the site with caps or plugs on all open ends.
+
+## Duct sections shall be stored indoors or under weatherproof cover at the site.
+
+## Duct stored outdoors without cover accumulates rainwater, dirt, and construction debris that is difficult to remove once the duct is installed. {note}
+
+## Flexible duct shall be stored in its original packaging, indoors, and shall not be stored where it will be walked upon or subjected to loads that deform the inner core.
+
+## Liner and external insulation shall be stored in dry conditions and protected from moisture.
+
+## Insulation that has been saturated shall be discarded and replaced; it shall not be dried and re-installed.
+
+## Wet insulation loses R-value, can support microbial growth, and if installed wet will dry unevenly and can separate from the duct face. {note}
+
+## Duct sections, fittings, and accessories shall be handled with care during installation to avoid denting, crushing, or deforming the duct.
+
+## Rectangular duct used as a stepladder or work surface is damaged and shall not be installed.
+
+## Workers shall not walk on flat-oval or round duct.
+
+# Identification {toc}
+
+## Ductwork shall be identified with system type and direction of flow at each branch, at each access door, and at intervals not exceeding 50 ft on straight runs, in conformance with SMACNA and the IMC.
+
+## Identification shall include the system designation (SAL-1, RA-2, EA-3, etc.) and an airflow direction arrow.
+
+## Fire dampers and smoke dampers shall be tagged with the damper tag number matching the damper schedule.
+
+## Access doors shall be labeled with the device served.
+
+## Insulated ductwork identification shall be placed on the outer face of the insulation jacket using stencil or adhesive label.
+
+## Where the Engineer specifies a color-coding scheme for system types, the Contractor shall apply the designated colors.
+
+## Color coding is not required by SMACNA. {note}
+
+# Warranty {toc}
+
+## The Contractor shall warrant the ductwork installation, including fabrication, seams, joints, sealing, insulation, hangers, and accessories, against defects in materials and workmanship for a period from the date of substantial completion as specified below.
+
+## The warranty shall cover failures, excessive leakage, hanger failures, sealant failures, and insulation separation from duct surfaces.
+
+## Damper actuators and other mechanical accessories shall carry the manufacturer's warranty, which the Contractor shall assign to the Owner at project closeout.
+
+## Warranty Period Datasheet {toc}
+
+```datasheet
+label: Ductwork Installation Warranty Period
+type: select
+options:
+ - "1 year from substantial completion"
+ - "2 years from substantial completion"
+default: "1 year from substantial completion"
+```
+
+## Where leakage testing results that are borderline (passing but within 10 percent of the acceptance criterion) are accepted, the Engineer may require a re-test during the warranty period to confirm that seasonal temperature cycles, building settlement, and sealant aging have not caused the leakage rate to increase to a failing value.
+
+## Re-testing under warranty shall be at the Contractor's expense.
+
+## The Contractor shall maintain access to all tested duct sections throughout the warranty period by keeping access doors clear of finishes, equipment, and storage.