1 Scope
NOTE This standard covers the selection, performance rating, materials, construction, and installation of room-side air distribution devices for HVAC systems in commercial and institutional buildings. (1.1)
NOTE Devices covered include supply diffusers of all common configurations (square plaque, round, perforated face, linear slot, swirl, displacement), return and exhaust grilles, transfer grilles, light-troffer-integrated diffusers, and security/correctional-grade grilles. (1.2)
NOTE Construction materials, finishes, frame styles for various ceiling systems, integral opposed-blade dampers (OBDs), equalizing grids, scoops, and other accessory provisions are addressed. (1.3)
1.4 Role of Air Distribution Devices
NOTE Air distribution devices are the visible end of the HVAC system and the interface between the conditioned air stream and the occupant. (1.4.1)
NOTE Properly selected devices deliver the design airflow at acceptable noise, distribute that airflow across the occupied zone without drafts or stagnation, and present a clean architectural appearance consistent with the ceiling system into which they are installed. (1.4.2)
NOTE Poorly selected or installed devices cause every category of occupant complaint that mechanical systems are blamed for: drafts, hot and cold spots, noise, condensation on the face, dust streaking on the ceiling, and visible architectural conflicts with the lighting and ceiling layout. (1.4.3)
NOTE Selection requires coordinated attention to airflow, throw, terminal velocity, room geometry, ceiling height, the location of occupants relative to the device, and the acoustic environment. (1.4.4)
1.5 Performance ratings shall conform to ANSI/ASHRAE 70 and to AHRI 885 as applicable.
1.6 Air diffusion performance for the occupied space shall be evaluated per the ADPI methodology described in ASHRAE Handbook — Fundamentals, Space Air Diffusion chapter.
2 Referenced Standards
2.1 Equipment, materials, and installation shall comply with the latest editions of the following standards adopted by the project jurisdiction.
| Standard |
Title |
| ANSI/ASHRAE 70 |
Method of Testing for Rating the Performance of Air Outlets and Inlets |
| ANSI/AHRI 885 |
Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets |
| ANSI/AHRI 880 |
Performance Rating of Air Terminals (cross-reference for sound and pressure characterization of upstream terminal units only — not applicable to outlets) |
| ASHRAE Handbook — Fundamentals |
Space Air Diffusion chapter (ADPI methodology, throw, terminal velocity, room load criteria) |
| ANSI/ASHRAE/IES 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 |
| ASTM E84 |
Standard Test Method for Surface Burning Characteristics of Building Materials |
| 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 |
| UL 555S |
Standard for Smoke Dampers (applicable where security/blast/fire-rated grilles are required to include damper functionality) |
| SMACNA HVAC Air Duct Leakage Test Manual |
Referenced for duct interface only — does not govern outlet device construction |
| ICC A117.1 / ADA Standards |
Accessible and Usable Buildings and Facilities (clearance and projection limits for wall-mounted devices in accessible routes) |
2.2 Where a specific edition is referenced in contract documents or by the local building code, that edition shall govern.
3 Submittals
3.1 Action Submittals
3.1.1 The Contractor shall submit the following for the Engineer's review and return prior to procurement or installation of the corresponding devices.
3.1.2 No device shall be procured for installation until the associated submittal has been reviewed and returned with no outstanding engineering questions.
3.1.3 The Contractor shall submit the following action submittal deliverables
- Product data sheets for each device type, including face dimensions, neck/throat dimensions, frame style, material, finish, listed pattern controllers or adjustable cores where provided, and integral accessories (OBD, equalizer, scoop)
- Performance data tables or selection curves from the manufacturer showing, at the design neck velocity or face velocity for each tagged outlet: total airflow (cfm), throw to 50/100/150 fpm terminal velocities (in feet), neck total pressure (in. w.g.), and NC rating, all derived from testing per ASHRAE 70 and AHRI 885
- ADPI calculation summary for each typical room type served, demonstrating that the selected outlet, located at the indicated position with the design airflow, achieves an ADPI of not less than the value specified for the room type
- Finish samples or color chip data for each finish specified, including standard white, custom paint colors, and any anodized or special finishes
- Frame style cross-section detail confirming compatibility with the ceiling system or wall construction shown on the architectural drawings, including the ceiling tile size and grid module for lay-in installations, the plaster ring detail for plaster ceilings, and the surface-mount frame detail for hard-lid ceilings
- Schedule of devices keyed to the mechanical drawings and air outlet schedule, listing tag, model, size, neck/throat, finish, frame style, OBD requirement, and design airflow
☑ Product data — each device type
☐ Performance data — throw at 50/100/150 fpm, NC, neck pressure
☐ ADPI calculation summary for each room type
☐ Finish samples or color chips
☐ Frame style cross-section detail for each ceiling/wall type
☐ Device schedule keyed to drawings
3.2 Closeout Submittals
3.2.1 At substantial completion and before final acceptance of the air distribution system, the Contractor shall provide:
- As-built device schedule reflecting any field substitutions, including the substituted manufacturer and the engineering review documentation for each substitution
- Operation and maintenance instructions for removable cores, adjustable pattern controllers, and integral dampers, including the position-setting procedure established during balancing
- TAB report sections for each device documenting the measured airflow at final balance, in coordination with Testing Adjusting And Balancing
- Warranty documentation from the manufacturer covering finish and material defects
☑ As-built device schedule reflecting field substitutions
☐ Operation and maintenance instructions for cores, controllers, and dampers
☑ TAB report sections documenting measured airflow at final balance
☑ Warranty documentation covering finish and material defects
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1 Devices shall be manufactured by a company with a minimum of five years of continuous experience producing air distribution outlets and inlets for commercial HVAC service.
4.1.2 The manufacturer shall publish performance data derived from independent or accredited in-house testing per ASHRAE 70 and AHRI 885.
4.1.3 The manufacturer shall maintain a current published catalog covering the full range of devices supplied.
4.1.4 The manufacturer shall maintain a domestic stock of replacement cores and damper assemblies sufficient to support the project for a minimum of ten years after substantial completion.
4.2 Single-Source for Each Device Family
4.2.1 For each room type and each visible ceiling area, all devices of the same category shall be supplied by a single manufacturer to maintain consistent appearance, frame profile, and finish.
NOTE Mixing manufacturers within a continuous visible area produces visible variation in face pattern, border profile, and color match that is unacceptable and is a frequent source of punch-list items. (4.2.2)
4.3.1 Published performance data shall be derived from testing in accordance with ANSI/ASHRAE 70.
4.3.2 Sound ratings shall be developed in accordance with AHRI 885.
4.3.3 The Contractor shall not substitute devices for which performance data are not derived from these procedures.
4.3.4 Manufacturer data sheets shall clearly identify the test standard applied.
4.4 Mock-Up
4.4.1 Where the project includes more than 50 devices of the same model in a continuous visible ceiling area, or where the Architect or Engineer specifies it, the Contractor shall install a mock-up of one device of each type, installed in the actual ceiling assembly with the proposed finish, before procuring the balance of the order.
4.4.2 The Architect and Engineer shall review the mock-up for finish match, frame fit, and visible appearance before the Contractor releases the full procurement.
5 Environmental and Service Conditions
5.1 Air distribution devices shall be selected for the environment in which they will operate.
NOTE Devices in normal interior conditioned spaces use standard steel or aluminum construction with painted or anodized finishes, while devices in showers, natatoriums, kitchens, and other high-humidity or corrosive environments require material selection appropriate to the service. (5.2)
5.3 Interior Conditioned Spaces
5.3.1 Steel or aluminum construction with the manufacturer's standard powder-coat finish is appropriate for normal interior office, classroom, retail, and similar occupancies.
5.3.2 The standard finish shall be matte white, off-white selected to match common acoustical ceiling tile colors.
5.3.3 Where the architect specifies a custom color, the manufacturer's color-match service shall be used.
5.4 High-Humidity and Wet Areas
5.4.1 In bathrooms with adjacent showers, in natatoriums and indoor pool areas, in kitchens, and in similar wet or high-humidity environments, devices shall be aluminum or stainless steel construction.
NOTE Standard steel devices with painted finishes corrode at the cut edges and at fastener penetrations under sustained moisture exposure, even when the visible face appears acceptable for the first few years of service. (5.4.2)
5.5 Corrosive Atmospheres
5.5.1 In laboratory exhaust applications, in spaces with chemical processing, and in indoor pools with chlorine-based water treatment, stainless steel (Type 316 preferred over Type 304 in chloride-rich environments) shall be specified.
5.5.2 Aluminum is acceptable in many corrosive applications but shall not be used where chloride or alkaline cleaning solutions contact the device.
5.6 Exterior and Outdoor Air Applications
5.6.1 Where intake or exhaust devices are installed at the exterior of the building, they shall be specifically rated for outdoor service with appropriate provisions for water shedding, insect screens, and the wind loads imposed at the device location.
5.6.2 Standard interior diffusers and grilles shall not be installed at exterior wall penetrations; outdoor service requires louvers or weather-rated grilles, which fall outside the scope of this standard.
5.7 Default Device Material Selection
● Steel, ASTM A653, with manufacturer's standard powder-coat finish (interior conditioned)
○ Extruded or formed aluminum, ASTM B209, anodized or powder-coated finish
○ Stainless steel, ASTM A240, Type 304 (wet areas)
○ Stainless steel, ASTM A240, Type 316 (corrosive/chloride environments)
6.1 Airflow, Throw, and Terminal Velocity
NOTE The performance of a supply outlet is characterized by its airflow rate (cfm), by the throw to 50, 100, and 150 fpm terminal velocities, by the neck total pressure required to deliver that airflow (in. w.g.), and by the sound level produced at the design airflow (NC). (6.1.1)
6.1.2 All four characteristics shall be verified against published data for the selected device at the design conditions.
6.1.3 Throw to 100 fpm terminal velocity shall match the room geometry such that the 100 fpm boundary reaches approximately to the perimeter wall (or to the opposing diffuser's 100 fpm boundary in multi-diffuser rooms) at the ceiling level, with the supply jet falling into the occupied zone at velocities below 50 fpm.
NOTE Throw to 100 fpm terminal velocity is the dominant comfort metric for cooling-mode supply diffusers in occupied spaces; selecting a device only by neck size or by airflow without considering throw and NC is a leading cause of comfort and noise complaints. (6.1.4)
6.1.5 Design Throw Setpoints
440
468101215182125303540
Default: 12 ft
Per drawings
660
6810121518212530405060
Default: 18 ft
Per drawings
325
34568101215182125
Default: 8 ft
Per drawings
NOTE For heating-mode supply diffusers serving spaces with the supply air above the room temperature, the buoyancy of the warm jet works against the diffuser's downward throw. (6.1.6)
6.1.7 Where the same ceiling-mounted diffuser is used for both heating and cooling supply, the Engineer shall verify that the heating-mode throw is sufficient to reach the occupied zone; otherwise warm air will stratify at the ceiling and the occupied zone will remain cold.
6.1.8 For combined heating and cooling diffusers in spaces with ceilings above 12 ft, the design team shall verify heating performance with a separate calculation or shall use diffusers with adjustable pattern controllers (see Adjustable Pattern Controllers).
NOTE Throw-to-mounting-height ratios of 0.5 to 0.75 are typical for cooling-mode diffusers. (6.1.9)
NOTE ADPI is the percentage of occupied-zone locations where the local effective draft temperature falls within the comfort envelope and is the consensus single-number metric for cooling-mode air diffusion quality. (6.2.1)
6.2.2 ADPI shall be calculated or estimated for each typical room type, with selection of throw and airflow tuned to achieve the target.
6.2.3 ADPI Target Selection
70% — minimum acceptable (lowest-cost spaces only)
80% — standard commercial target
85% — high-quality office and classroom
90% — premium quality, conference rooms and executive spaces
NOTE ADPI targets above 90% generally require either careful pattern adjustment or higher diffuser counts than the minimum required by airflow alone. (6.2.4)
6.2.5 Where the design room load is high (above approximately 30 Btu/h/ft² sensible), achieving ADPI ≥ 80% with ceiling-mounted diffusers shall require careful attention to the ratio of throw to characteristic room length per ASHRAE Fundamentals; under-throwing such rooms produces stagnant occupied zones with poor mixing.
6.3 Noise Criterion (NC)
6.3.1 NC rating at the design airflow shall be selected based on the room's intended use.
6.3.2 NC shall be derived per AHRI 885, which addresses the conversion from manufacturer outlet sound power data (from ASHRAE 70 testing) to estimated sound pressure in the receiving room using a standardized room correction.
NOTE Bare manufacturer sound power numbers are not directly comparable to room NC without applying the room correction. (6.3.3)
6.3.4 NC Target Selection
NC 25 — concert halls, recording studios, executive offices
NC 30 — private offices, classrooms, conference rooms, hospitals
NC 35 — open offices, retail, restaurants, libraries
NC 40 — corridors, lobbies, light commercial
NC 45 — kitchens, mechanical/service areas, gymnasiums
NOTE Each manufacturer applies a room correction to convert published outlet sound power into the room NC value shown in the published selection table, typically assuming a room with 10 dB of room absorption and the outlet at a specified distance from the receiver. (6.3.5)
6.3.6 For rooms with significantly different absorption (highly reverberant spaces like atria, lobbies with hard surfaces), the Engineer shall apply additional room correction per AHRI 885 where the published assumptions do not represent the actual application.
6.3.7 AHRI 885 Room Correction Method
● Manufacturer's published NC at design airflow (standard room correction)
○ AHRI 885 calculation by Engineer using project room absorption and distance
6.4 Neck Pressure and System Resistance
6.4.1 The neck total pressure of the selected device at the design airflow is the resistance the device adds to the duct system and shall be included in the fan static pressure calculation for the system.
6.4.2 Devices with integral OBDs add additional pressure drop when the OBD is throttled; the Engineer shall account for the throttled OBD pressure drop in the duct design, not the full-open value.
6.4.3 Neck Total Pressure
0.020.3
Default: 0.08 in. w.g.
7 Supply Diffusers — Types and Selection
7.1 Square and Rectangular Plaque Diffusers
NOTE Square and rectangular plaque diffusers discharge a horizontal jet in one, two, three, or four directions across the ceiling, with the supply air attaching to the ceiling surface by Coanda effect and decaying along the throw distance. (7.1.1)
NOTE The directional pattern is set at the factory or selected from a removable core; one- and two-way patterns are used where the diffuser is near a wall or corner and four-way patterns are used in open-area locations away from walls. (7.1.2)
7.1.3 Plaque Diffuser Discharge Pattern
○ 1-way (against perimeter wall)
○ 2-way opposite (between two walls)
○ 2-way adjacent (corner installation)
○ 3-way (one wall adjacent)
● 4-way (open area, no adjacent wall)
NOTE Plaque diffusers are the standard for general cooling-mode supply in office, classroom, and retail spaces with ceilings of 8 to 14 ft. (7.1.4)
7.1.5 Plaque diffusers shall not be used for heating-mode supply where the horizontal discharge does not penetrate the warm ceiling layer; for heating-only spaces use a downward-projecting diffuser such as a swirl diffuser or a sidewall grille set to project downward.
7.1.6 Plaque Diffuser Face and Neck Sizes
6 × 6
9 × 9
12 × 12
15 × 15
18 × 18
24 × 24
Per drawings
7.2 Round Ceiling Diffusers
NOTE Round ceiling diffusers provide a radial 360-degree discharge pattern and are used in open areas where a uniform horizontal throw in all directions is desired. (7.2.1)
7.2.2 Round diffusers shall not be installed close to walls (within one diffuser diameter) because the wall obstructs the radial pattern and produces stagnation on the wall side.
7.2.3 Round Diffuser Face Diameter
7.3 Linear Slot Diffusers
NOTE Linear slot diffusers discharge a long, thin supply jet from a slot (or multiple parallel slots) extending along a continuous run, used to wash perimeter walls and glazing, at the edges of architectural soffits, and in open-plenum or exposed-ceiling applications where the linear form integrates with linear lighting fixtures. (7.3.1)
NOTE The number of slots per linear foot affects throw, neck pressure, and NC: more slots at the same airflow give higher throw and lower NC; fewer slots give the opposite. (7.3.2)
7.3.3 Slot pattern controllers (adjustable internal blades that bias the jet direction) shall be specified where the same linear slot must serve both heating and cooling modes — set to throw outward across the ceiling in cooling and downward into the occupied zone in heating.
7.3.4 Linear Slot Diffuser Selection
1 slot
2 slots
3 slots
4 slots
6 slots
8 slots
220
23456810121520
Default: 4 ft
Per drawings
○ Fixed horizontal discharge (cooling only)
● Field-adjustable pattern controller (combined heating and cooling)
○ Vertical (downward) discharge (heating-dominant or makeup-air)
7.3.5 End caps on continuous linear slot runs shall be coordinated with the architectural design, since exposed end caps are visible at the ends of each run and may interrupt a continuous architectural line.
7.3.6 Where multiple slot sections are joined to form a continuous run, the joints shall align with the architectural module and be sealed at the inactive (non-airflow) length to maintain visual continuity.
7.4 Swirl and Circular-Throw Diffusers
NOTE Swirl diffusers discharge a strong rotational supply jet that mixes rapidly with room air, producing high induction and a relatively short throw. (7.4.1)
NOTE Swirl diffusers are appropriate for spaces with high ceilings (above 12 ft) where conventional plaque diffusers would over-throw the room, and for cold supply or high-temperature-differential applications where rapid mixing is essential to avoid drafts at the occupied level. (7.4.2)
7.4.3 Swirl Diffuser Size
7.5 Displacement Diffusers
NOTE Displacement diffusers introduce conditioned supply air at low velocity (typically 50 to 80 fpm at the device face) near the floor, allowing the cool supply air to spread along the floor and rise by buoyancy as it picks up heat from occupants and equipment. (7.5.1)
NOTE Displacement systems can deliver superior air quality in the breathing zone with reduced fan power compared to overhead mixing systems, but require careful coordination with room layout, internal partitions, and heat sources. (7.5.2)
7.5.3 Displacement Diffuser Configuration
Not used on this project — overhead mixing system
Floor-mounted, half-round wall integrated
Floor-mounted, quarter-round corner integrated
Floor-mounted, free-standing column
Sidewall-mounted at low elevation
7.5.4 Displacement diffusers shall not be specified in rooms with cooling loads above approximately 30 Btu/h/ft² because the supply air temperature required to remove the load creates unacceptable cold-feet sensation at the supply jet.
NOTE Displacement is best applied to rooms with moderate loads, tall ceilings, and clear floor-to-return paths. (7.5.5)
8 Returns, Exhausts, and Transfer
8.1 Return Grilles
NOTE Return grilles collect air from the room for return to the air handler; because the suction zone of an inlet is small, return grille location is less critical for room air motion than supply diffuser location, but improper return location can short-circuit supply air directly back to the return without conditioning the occupied zone. (8.1.1)
8.1.2 Return Grille Style and Size
○ Fixed louver — horizontal blades
○ Fixed louver — 45-degree deflection blades
○ Eggcrate — 1/2 in. × 1/2 in. cell
● Eggcrate — 1/2 in. × 1 in. cell (general purpose)
○ Perforated face (matches supply diffuser appearance)
12 × 12
18 × 18
24 × 12
24 × 24
36 × 12
36 × 24
48 × 24
Per drawings
8.1.3 Return grille face velocity shall be selected based on the NC target for the room and the proximity of the grille to occupied areas.
NOTE Face velocities of 400 to 500 fpm are typical for general office and classroom return grilles; lower face velocities (300 to 400 fpm) are appropriate for NC 30 rooms and quieter; higher face velocities (500 to 600 fpm) are acceptable in corridors and back-of-house areas. (8.1.4)
8.1.5 Face velocities above 700 fpm shall not be used because they produce audible noise and increased system static pressure.
8.1.6 Return Grille Face Velocity
200700
200300400500600700
Default: 400 fpm
8.2 Exhaust Grilles
NOTE Exhaust grilles serve restrooms, janitor closets, and other spaces from which contaminated air shall be removed without returning it to the supply system, typically constructed identically to return grilles but connected to a dedicated exhaust duct system. (8.2.1)
8.2.2 Where the exhaust duct conveys grease, moisture, or fumes that are corrosive, the grille shall match the duct material to avoid galvanic or corrosion incompatibility at the duct interface.
8.2.3 Exhaust Grille Style
○ Same as return grille style (general exhaust)
○ Louver-type with 1/2 in. blade spacing (toilet exhaust)
● Eggcrate (general exhaust)
○ Stainless steel construction (corrosive exhaust)
8.3 Transfer Grilles
NOTE Transfer grilles allow air to pass from one space to an adjacent space without dedicated ductwork, for example allowing supply air from an office to relieve into a return air corridor. (8.3.1)
8.3.2 Transfer grilles in fire-rated assemblies require fire dampers or shall not be installed in the rated assembly; the Contractor shall coordinate with the fire-rated assembly schedule on the architectural drawings to confirm that each transfer grille location does not penetrate a fire-rated assembly without appropriate fire-resistance provisions.
8.3.3 Transfer grilles shall be acoustically rated where they cross from a private office or conference room into a corridor or open area.
NOTE Uninsulated transfer grilles allow speech to pass directly between spaces and undermine the acoustic privacy of the originating space; acoustic transfer grilles include a baffled, lined plenum behind a louver face that absorbs speech-band sound while permitting airflow. (8.3.4)
8.3.5 Transfer Grille Type
○ Standard louver — no acoustic treatment (corridor return paths)
○ Acoustically lined transfer (private office to corridor or conference room transfer)
● Not used on this project
9 Frame Styles for Ceiling and Wall Systems
9.1 Lay-in Ceiling Frames (Suspended T-Bar Grid)
NOTE Lay-in frames are designed to drop into a standard suspended acoustical ceiling T-bar grid (typically 24 in. × 24 in. or 24 in. × 48 in. nominal modules), with the face panel at the full module dimension and the visible flange overlapping the T-bar flush with the surrounding ceiling tiles. (9.1.1)
NOTE Lay-in frames are the default for office, classroom, and corridor ceilings constructed with suspended acoustical tile. (9.1.2)
9.1.3 Lay-in Frame Ceiling Grid Module
24 × 24
24 × 48
Concealed grid (proprietary tile system)
Not applicable — non-lay-in ceiling
9.2 Surface-Mount Frames (Hard-Lid Ceilings and Walls)
NOTE Surface-mount frames are installed on a finished surface (gypsum board ceiling, plaster ceiling, or wall) with a visible border flange screwed to the surface and a duct collar penetrating the surface behind the device. (9.2.1)
NOTE Surface-mount frames are used in hard-lid ceilings, in retail and hospitality where the suspended ceiling has been replaced by a finished hard surface, and at wall-mounted device locations. (9.2.2)
9.2.3 Surface-Mount Frame Surface Type
● Painted gypsum board
○ Plaster
○ Finished wood or paneling
○ Concrete or masonry
9.3 Plaster (Mud-In) Frames
NOTE Plaster frames (also called mud-in or snap-in frames) are installed before the plaster or skim-coat finish is applied and are designed so that the plaster surface terminates flush with the device face, with no visible frame border. (9.3.1)
NOTE The mud-in result is a clean device face with no border interruption — preferred in high-end architectural plaster ceilings, in museum and gallery spaces, and in healthcare patient rooms where surface continuity supports cleanability. (9.3.2)
9.3.3 Plaster frames shall be coordinated with the plastering trade to ensure the rough opening is correctly sized and the frame is installed at the correct elevation before plaster work begins.
9.3.4 Plaster Frame Selection
○ Yes — coordinate with plastering trade
● No — lay-in or surface-mount frame as scheduled
9.4 Light Troffer-Integrated Diffusers
NOTE Light-troffer-integrated diffusers combine a fluorescent or LED troffer light fixture and a linear slot diffuser into a single ceiling unit, used where the architectural design calls for the lighting and HVAC modules to align in the ceiling and where both must be located in the same area. (9.4.1)
NOTE The HVAC connection is to a duct collar at the rear of the troffer; the diffuser slots run along the long edges of the troffer. (9.4.2)
9.4.3 The HVAC contractor shall confirm at submittal that the selected troffer fits the electrical fixture supplied for the troffer body, and that the connection sequence allows both trades to complete their work without conflict.
9.4.4 Troffer-integrated diffusers shall not be used for rooms with high cooling loads, because the troffer's linear slot is generally too small to handle the airflow without excessive NC.
9.4.5 Light-Troffer-Integrated Diffuser Selection
● Not used — separate light fixtures and diffusers
○ Used — coordinate with lighting fixture model on electrical drawings
10 Construction, Cores, and Accessories
10.1 Face and Frame Construction
10.1.1 Steel devices shall be fabricated from cold-rolled steel sheet of 22 gauge minimum for the face and 20 gauge minimum for the frame.
10.1.2 Heavier gauges shall be used where the device dimensions exceed approximately 24 in. on a side or where the device serves a high-static-pressure application.
10.1.3 Aluminum devices shall be fabricated from extruded or formed aluminum sheet of 0.040 in. minimum for face and frame, with extruded sections used for linear slot diffuser bodies and frames.
10.1.4 Face Material
● Steel sheet, 22 gauge face / 20 gauge frame
○ Steel sheet, heavier gauge per manufacturer for large devices
○ Extruded or formed aluminum
○ Stainless steel, 22 gauge face / 20 gauge frame
10.1.5 All visible faces shall be free of burrs, sharp edges, and visible welds.
10.1.6 Fasteners on visible surfaces shall be flush-finished and color-matched to the device finish.
10.1.7 Concealed structural fasteners (screws holding the back-pan to the frame, etc.) may be standard plated steel.
10.2 Removable Cores
NOTE Diffusers with removable cores allow the directional pattern of the device to be changed after installation without removing the entire device from the ceiling, particularly valuable in renovation projects and where the original directional selection proves incorrect during the TAB phase. (10.2.1)
10.2.2 The removable core shall be secured by captive screws or a positive latch mechanism that cannot release accidentally; gravity-only retention is not acceptable.
10.2.3 Removable Core Selection
● Yes — captive screw or positive latch retention
○ No — factory-fixed pattern (lower cost, no field adjustability)
10.3 Opposed-Blade Dampers (OBDs)
NOTE An opposed-blade damper (OBD) is an integral damper assembly mounted in the neck of the diffuser or grille, used to throttle airflow at the device for balancing purposes. (10.3.1)
NOTE OBDs are an alternative to in-duct volume control dampers and are typically less effective at balancing because they produce more noise per unit of throttling and because they are visible to the occupant. (10.3.2)
10.3.3 OBDs at the device shall not be the primary balancing mechanism for the system.
10.3.4 The duct system shall include volume control dampers in branch ducts per Hvac Ductwork for primary balancing, with OBDs at devices used only for fine trim of airflow within ±20% of design. NOTE Specifying OBDs in lieu of volume control dampers is a frequent cost-cutting practice that prevents the TAB contractor from balancing the system and results in noisy devices throttled to choke airflow that should have been balanced upstream. (10.3.5)
10.3.6 OBD Selection
● Yes — OBD provided for fine trim only (branch VCD provides primary balancing)
○ Yes — OBD as primary balancing mechanism (small systems with simple branches)
○ No — balancing entirely by branch VCDs
● Through the device face (visible slot or key access)
○ Through the device neck (concealed, key access only)
○ Not applicable — no OBD
10.4 Equalizing Grids and Scoops
NOTE An equalizing grid is a set of adjustable internal blades upstream of the device face that smooths and equalizes the airflow across the neck of the device when connected to a duct with non-uniform velocity profile. (10.4.1)
10.4.2 Equalizing grids shall be specified where the duct geometry upstream of the device does not provide a minimum of three duct diameters of straight duct entering the neck; otherwise the discharge pattern will be skewed and the throw will be asymmetric.
NOTE A scoop (also called a take-off) is a curved or angled diverter inside the main duct at the branch connection that directs a portion of the main airflow into the branch; scoops are not part of the device itself but are commonly bundled with the device order. (10.4.3)
10.4.4 Where high-induction or branch-flow-equalization devices are required for the duct system, the Contractor shall verify that scoops are coordinated between the duct fabrication and the device order.
10.4.5 Equalizing Grid and Scoop Selection
○ Yes — where boot connection or short duct upstream
● No — straight duct upstream of device neck
○ Conical or 45-degree branch take-off in main duct
○ Bullhead tee with scoop diverter
● Coordinated with duct fabrication (not part of device order)
○ Not applicable
10.5 Adjustable Pattern Controllers
NOTE Adjustable pattern controllers (also called anti-smudge rings, diffuser cones, or drop pattern adjustors) alter the discharge angle of a diffuser between horizontal (cooling mode, attached to ceiling) and downward (heating mode, projecting into the occupied zone). (10.5.1)
NOTE Adjustable pattern controllers are valuable in spaces served by a single device for both heating and cooling, particularly with high ceilings or with significant heating-mode supply temperature differentials. (10.5.2)
10.5.3 Adjustable pattern controllers shall be field-set during the TAB process based on the system operating mode that best serves the occupied zone.
10.5.4 In rooms with prolonged occupancy by stationary occupants (open offices), the cooling-mode horizontal pattern is generally preferred and the controller shall be set accordingly even when heating supply is occasionally used.
10.5.5 In intermittent-occupancy spaces with infrequent heating use, the controller may be set for downward heating performance, accepting somewhat poorer cooling distribution.
10.5.6 Adjustable Pattern Controller Selection
○ Yes — required for combined heating and cooling supply with tall ceilings or high ΔT
● No — single-mode service or moderate conditions where fixed pattern is adequate
10.6 Security and Correctional Grilles
NOTE Security and correctional grilles are heavy-duty grilles installed in correctional facilities, behavioral health units, holding cells, and similar applications where the grille shall resist tampering, ligature attempts, and contraband concealment. (10.6.1)
10.6.2 Security and correctional grille construction shall be heavy steel or stainless steel with tamper-resistant fasteners and shall be selected from a manufacturer's published security or correctional product line.
10.6.3 Where security grilles also serve as fire dampers, they shall be listed to UL 555 or UL 555S as applicable.
10.6.4 Security/Correctional-Grade Construction Selection
● Not required (general commercial/institutional)
○ Behavioral health — anti-ligature, smooth face, tamper-resistant
○ Correctional — heavy gauge, security fasteners, anti-contraband perforation
○ Correctional with integral fire/smoke damper (UL 555/555S listed)
10.6.5 Tamper-resistant fasteners shall be of a type for which the access tool is not commercially available to occupants — typically a manufacturer-specific bit or driver supplied to the facility maintenance staff at substantial completion.
10.6.6 Where ligature resistance is required, all exposed edges shall be radiused or chamfered and all fasteners shall be flush and recessed below the face surface, presenting a smooth profile that cannot be used to anchor a ligature point.
11 Finishes
11.1 Standard manufacturer finish for steel devices in interior commercial applications shall be electrostatically applied powder-coat in a baked finish.
11.2 Standard color shall be matte white (RAL 9010 or equivalent) selected to match common acoustical ceiling tile.
11.3 Custom colors shall be obtained from the manufacturer's color-match program with submittal of a sample chip from the Architect for approval before production.
NOTE Aluminum devices may be powder-coated or anodized; clear anodized finish provides a natural metallic appearance and is corrosion-resistant, and color anodizing is available in a limited palette of metallic colors. (11.4)
NOTE Stainless steel devices are typically finished as #4 satin (brushed) or as a powder-coat-painted surface where color is required; mirror-polish finishes show fingerprints and water spots and are not recommended for general interior use. (11.5)
11.6 Standard Finish Selection
Powder-coat matte white (RAL 9010 or equivalent)
Powder-coat custom color (Architect's selection)
Clear anodized aluminum
Color anodized aluminum
#4 satin stainless steel
Mill finish (concealed devices only)
11.6.1 Surface burning characteristics of any non-metal finish material applied to the device (gaskets, sealing strips, foam inserts within the device assembly) shall conform to ASTM E84 with a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 when the device is installed in plenum or ceiling assemblies subject to NFPA 90A.
12 Installation
12.1 Coordination with Ceiling Trades
12.1.1 Air distribution devices shall be installed in coordination with the ceiling, lighting, and fire protection trades.
12.1.2 The Contractor shall participate in coordination drawings (BIM or 2D as established for the project) that show device locations, ceiling grid alignment, light fixture positions, sprinkler heads, and other ceiling-mounted devices.
12.1.3 Conflicts shall be resolved before any ceiling element is installed; field relocation of devices to avoid lighting fixtures or sprinklers after the ceiling grid is established produces visible misalignment with the grid module and is not acceptable.
12.1.4 Ceiling Coordination Procedure
● BIM coordination required — device locations finalized at coordination meeting
○ 2D coordination drawings — device locations finalized before ceiling layout
○ Field coordination — devices follow ceiling grid as installed
12.2 Mounting in Lay-in Ceiling Grids
12.2.1 Devices in lay-in ceiling grids shall be supported by hangers attached independently to the structure above, not by the ceiling grid alone.
12.2.2 The lay-in flange of the device positions the device in the grid module but shall not carry the weight of the device, including the weight of the connected flexible duct.
NOTE Independent support of devices is required by IBC and applicable building codes; ceiling grids are not rated to carry concentrated point loads from suspended HVAC devices. (12.2.3)
12.2.4 A minimum of two safety chains, wires, or rods shall be installed from structure to the device frame at diagonally opposite corners.
12.2.5 Where the device weight exceeds 20 lb, additional support shall be provided per manufacturer's recommendations.
12.2.6 Devices shall be plumb and square in the ceiling grid, with the face flush with the surrounding ceiling tile surface within ±1/16 in.
12.3 Mounting in Hard-Lid Ceilings and Walls
12.3.1 Devices in hard-lid (gypsum board, plaster, or similar fixed surface) ceilings and walls shall be mounted in framed openings that accommodate the device frame and provide a flush installation.
12.3.2 Rough openings shall be cut to the manufacturer's published rough opening dimension; oversized or undersized openings shall not be patched with sealant or shims to fit the device.
12.3.3 The duct collar behind the device shall be sealed to the duct system and to the ceiling penetration to prevent plenum air bypass.
12.4 Duct Connection at Device
12.4.1 Devices shall be connected to the duct system by a sheet-metal collar of the same neck dimension as the device.
12.4.4 Device-to-Duct Connection Method
○ Sheet-metal collar with band clamp, sealed per duct seal class
○ Direct flange connection to rigid duct, sealed at flange
● Flexible duct to collar, draw-band and tape per [[sync/hvac-ductwork]]
12.5 Sealing of Plenum and Frame Interface
12.5.1 Where supply devices are installed in ceiling plenums used as return air plenums, the device frame shall be sealed to the ceiling surface to prevent supply air from short-circuiting around the frame and into the return plenum.
NOTE Where devices are installed in non-plenum (ducted) ceilings, the frame seal is primarily for visual continuity and acoustic continuity, preventing visible gaps and flanking sound paths around the device. (12.5.2)
12.6 Cleanliness and Protection
12.6.1 Devices shall be kept in protective packaging until the ceiling system is installed and the room is substantially complete.
12.6.2 Devices installed before ceiling completion shall be protected from drywall dust, paint overspray, plaster splash, and physical damage.
12.6.3 Devices contaminated with construction debris on the visible face shall be cleaned with manufacturer-approved methods; abrasive cleaning or cleaning with solvents that damage the powder-coat finish is not acceptable.
12.6.4 Where damage from construction activity cannot be repaired to match the surrounding devices, the damaged device shall be replaced at the responsible party's expense.
12.7 Removable Core Orientation
12.7.1 Diffusers with removable cores and adjustable patterns shall be installed with the pattern set to the design configuration shown on the mechanical drawings, and the pattern setting shall be re-verified during TAB.
12.7.2 Where the pattern is changed during TAB to improve room air distribution, the as-built device schedule shall record the final pattern setting for each device.
12.8 Adjustable Devices — Field Setting
12.8.1 Field-adjustable devices (those with adjustable pattern controllers, integral OBDs, or removable cores) shall be set during the TAB process by the TAB contractor in coordination with the system commissioning agent.
12.8.2 The OBD position, pattern controller position, and core orientation shall be recorded on the TAB report for each device.
13 Testing and Balancing
13.1 TAB Coordination
13.1.2 Balancing shall be performed with the cleaning of the system complete, the design filter media installed, and all devices in their final installed condition.
13.1.3 The TAB contractor shall set device OBDs and adjustable patterns as part of the balancing procedure and shall record final settings.
13.1.4 TAB Airflow Tolerance
● ±10% of design (standard commercial)
○ ±5% of design (critical applications — laboratory, healthcare, cleanroom)
13.2 Field NC Verification
NOTE Field NC verification at devices is generally not required for commercial projects unless the published manufacturer's performance data are unavailable or the design team has reason to believe that field conditions deviate significantly from the published assumptions. (13.2.1)
13.2.2 Where field NC verification is specified, the TAB or acoustic consultant shall measure A-weighted or octave-band sound pressure at the listener position with the system at design airflow, and shall compute NC by the standard tangent method.
13.2.3 Field NC Verification Selection
● Not required (rely on manufacturer's published NC at design airflow)
○ Required — measure at sensitive listener positions in occupied space
○ Required — measure at all rooms where NC ≤ 30 specified
13.3 Air Pattern Verification
13.3.1 For high-aspect-ratio rooms, rooms with non-standard geometries, and rooms with critical comfort requirements (executive offices, conference rooms, healthcare patient rooms), the TAB contractor or commissioning agent shall verify the supply air pattern by smoke test or by hot-wire anemometer traverse.
13.3.2 Devices with adjustable pattern controllers shall be adjusted to deliver the specified pattern.
13.3.3 Devices with fixed patterns that fail to deliver the design pattern shall be replaced at no cost to the Owner.
13.4 Smudging Inspection
13.4.1 After a minimum of 90 days of continuous operation, the ceiling surface around each ceiling-mounted supply diffuser shall be inspected for smudge patterns.
NOTE Smudging is the deposition of airborne dust on the ceiling surface where the supply jet entrains room air past the diffuser face; the smudge pattern indicates the actual discharge direction and can reveal pattern controllers that have shifted from their set position, devices with damaged face panels, and dust loading that exceeds the design assumptions for the room. (13.4.2)
13.4.3 Heavy smudging that disfigures the ceiling shall be cleaned and the cause investigated; in most cases the cause is excessive room dust loading rather than a device defect.
14 Delivery, Storage, and Handling
14.1 Devices shall be delivered to the site in the manufacturer's original protective packaging, with each device tagged with the project mark or device tag.
14.2 Storage shall be in a clean, dry, and weather-protected area.
14.3 Devices shall not be stacked in a manner that deforms the face panel or damages the frame.
14.4 Removable cores and adjustable internal components shall remain in the device package until immediately before installation to protect the painted finish from scuffs.
14.5 Where devices are delivered before the building is dried-in or before the ceiling system is ready, the Contractor shall maintain the devices in protected storage and shall not install devices in unprotected areas.
14.6 Installation in spaces exposed to construction dust, painting, or wet work shall be deferred until the surrounding work is complete.
15 Identification
15.1 Each device installed shall correspond to the tag indicated on the mechanical drawings and air outlet schedule.
15.2 Where the field-installed device is a substitution from the basis-of-design product, the as-built device schedule shall reflect the substitution.
15.3 Identification of devices in the ceiling for the Owner's facility staff shall be by the air outlet schedule, the as-built mechanical drawings, and the BAS device tagging conventions, not by labels on the visible device face; visible labels on diffusers and grilles are not acceptable for architectural reasons.
16 Warranty
16.1 The Contractor shall warrant the air distribution devices and their installation, including frame fit, face finish, integral dampers, and damper operability, for a period from the date of substantial completion as specified below.
16.2 Warranty shall cover finish defects (peeling, blistering, color shift), structural defects (warping, frame separation), damper failures, and any visible installation deficiency (misalignment, gap with surrounding ceiling, smudging caused by device defect).
16.3 Warranty Period
1 year from substantial completion
2 years from substantial completion
5 years on finish only, 1 year on installation
16.3.1 Finish warranty shall cover color-stability and adhesion for the period specified.
16.3.2 Sun-exposed devices (those receiving direct sunlight through perimeter glazing) shall be subject to manufacturer's UV-resistance specification, and finish failures attributable to UV exposure shall be addressed under the warranty if within the rated UV exposure limits.
17 Spare Parts
17.1 Spare Parts at Substantial Completion
☐ One spare core of each removable-core diffuser model (where used)
☐ One spare set of OBD operator keys/tools
☑ Color-matched touch-up paint for each finish (4 oz minimum per finish)
☐ Spare tamper-resistant fastener driver bits (for security/correctional applications)
17.1.1 Spare cores and parts shall be delivered to the Owner in labeled containers identifying the device model, the project tag of the corresponding installed device, and the date of delivery.
17.1.2 Where the manufacturer's standard color is selected, color-matched touch-up paint is generally available from the manufacturer in small quantities; for custom colors, the touch-up paint shall be ordered with the original device order to ensure batch match between the installed devices and the touch-up supply.