+---
+title: Makeup Air Units
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: Dedicated air-handling units that condition and deliver 100% outdoor
+ replacement air to offset large exhaust volumes in commercial, industrial, and
+ institutional buildings - commercial kitchens, laboratories, spray-finishing booths,
+ warehouses, manufacturing plants, and any occupancy where exhaust creates negative
+ pressure. Covers packaged rooftop and indoor units (roughly 1,000 to 150,000 CFM)
+ with direct gas-fired, indirect gas-fired, hot-water, steam, or electric heat; optional
+ evaporative, DX, or chilled-water cooling; supply fans; mixing/recirculating dampers;
+ and integral controls.
+ Not intended for: kitchen hood canopies, grease ducts, and fire suppression
+ ([[sync/kitchen-exhaust-systems]]); dedicated outdoor air systems serving occupant
+ ventilation loads ([[sync/dedicated-outdoor-air-systems]]); energy/heat-recovery
+ ventilators used as exhaust-transfer devices ([[sync/energy-recovery-ventilators]]);
+ VAV terminal units and zone supply distribution ([[sync/variable-air-volume-terminals]]);
+ discharge-duct sound attenuation ([[sync/hvac-sound-attenuators]]); cooling-coil
+ condensate drainage ([[sync/condensate-drainage-piping]]); standalone evaporative
+ coolers used as the primary cooling device ([[sync/evaporative-coolers]]); and supply
+ fan motor and drive specifications ([[sync/electric-motors]]).
+---
+
+# Scope {toc}
+
+## A makeup air unit (MAU) is a dedicated air handler that conditions and delivers 100% outdoor air to replace air removed by exhaust systems, maintaining a neutral-to-slightly-positive building pressure. Unlike a comfort air handler that recirculates room air, a MAU treats the full outdoor airstream from the design winter (and often summer) condition to a deliverable discharge temperature. Its sizing is driven by the total exhaust it offsets, not by a thermal zone load. This distinction governs every downstream decision in this standard — heat capacity, fan arrangement, casing, and controls all follow from the replacement-air mission. {note}
+
+## This standard governs packaged and field-assembled MAUs serving replacement-air functions, whether stand-alone or interlocked with kitchen hoods, laboratory exhaust, or general industrial exhaust. {note}
+
+## Equipment covered includes the heat section (direct gas-fired, indirect gas-fired, hot-water, steam, or electric), optional cooling section (evaporative, DX, or chilled-water), supply fan assembly, integral mixing and recirculating dampers, filtration, and the unit control package. {note}
+
+## The MAU shall be selected, furnished, and installed to deliver the scheduled supply airflow at the scheduled discharge temperature against the system external static pressure.
+
+## The MAU shall offset the total coincident exhaust it serves so that the building does not experience sustained negative pressure under any operating mode.
+
+## Kitchen hood canopies, grease duct, and hood fire-suppression systems are outside this standard and are governed by [[sync/kitchen-exhaust-systems]]; this standard covers only the makeup air unit that serves them. {note}
+
+## Dedicated outdoor air systems that provide full sensible-and-latent conditioning for occupant ventilation loads - rather than replacement air for exhaust - are governed by [[sync/dedicated-outdoor-air-systems]]. {note}
+
+## Energy- and heat-recovery ventilators used as exhaust-to-supply transfer devices are governed by [[sync/energy-recovery-ventilators]]; an energy-recovery wheel furnished as an integral MAU section remains within this standard. {note}
+
+## Zone-level supply distribution, VAV terminal units, and discharge sound attenuation are governed by [[sync/variable-air-volume-terminals]] and [[sync/hvac-sound-attenuators]] respectively. {note}
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+## Where a referenced standard has been superseded by the authority having jurisdiction, the currently adopted edition shall apply. {note}
+
+| Standard | Title |
+|----------|-------|
+| ANSI/ASHRAE Standard 62.1-2022 | Ventilation and Acceptable Indoor Air Quality |
+| ANSI/ASHRAE/IES Standard 90.1-2022 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
+| NFPA 54 (ANSI Z223.1)-2021 | National Fuel Gas Code |
+| NFPA 96-2021 | Ventilation Control and Fire Protection of Commercial Cooking Operations |
+| NFPA 33-2021 | Spray Application Using Flammable or Combustible Materials |
+| NFPA 70 (NEC)-2023 | National Electrical Code (Articles 430, 440, 500-516) |
+| UL 60335-2-40 | Electrical Heat Pumps, Air Conditioners and Dehumidifiers (replaces UL 1995 for new listings) |
+| UL 1995 | Heating and Cooling Equipment (superseded Jan 1, 2025; valid for in-service units) |
+| UL 795 | Commercial-Industrial Gas Heating Equipment |
+| CSA C22.2 No. 236 | Heating and Cooling Equipment (Canadian harmonized) |
+| ASHRAE Guideline 0-2019 | The Commissioning Process |
+| IMC 2021 | International Mechanical Code (Chapters 4 and 5) |
+| AMCA 210 | Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
+| SMACNA | HVAC Duct Construction Standards - Metal and Flexible, 4th Ed. |
+
+# Submittals {toc}
+
+## Action Submittals {toc}
+
+### The Contractor shall submit the following action submittals for review before fabrication or ordering:
+- Product data for the complete MAU including capacity ratings, fan curves, sound power data, and electrical characteristics.
+- Equipment schedule confirming scheduled airflow, discharge temperature, heating and cooling capacity, and external static pressure.
+- Dimensioned shop drawings showing unit footprint, weight, center of gravity, service clearances, curb interface, and discharge orientation.
+- Gas train piping diagram and combustion data for gas-fired units, including listing reference and high/low fire input.
+- Wiring diagram showing control sequence, exhaust interlock, and points of connection to the building automation system.
+- Listing and labeling documentation (UL 60335-2-40, UL 795, or equivalent) for the as-furnished configuration.
+- Structural reaction loads at support points for coordination with the structural engineer of record.
+
+```datasheet
+label: Action submittals required
+type: checkbox
+options:
+ - Product data and capacity ratings
+ - Equipment schedule
+ - Dimensioned shop drawings
+ - Gas train piping and combustion data
+ - Control wiring and interlock diagram
+ - Listing and labeling documentation
+ - Structural reaction loads
+default: [Product data and capacity ratings, Equipment schedule, Dimensioned shop drawings, Control wiring and interlock diagram]
+```
+
+## Closeout Submittals {toc}
+
+### The Contractor shall submit the following closeout submittals before substantial completion:
+- Operation and maintenance manuals covering startup, seasonal changeover, filter service, and burner maintenance.
+- Manufacturer startup and commissioning reports including measured airflow, discharge temperature, and interlock verification.
+- As-built control sequence and final balancing report for the supply fan and any return/relief fan.
+- Warranty documentation for the unit, heat exchanger, and any extended-coverage components.
+
+```datasheet
+label: Closeout submittals required
+type: checkbox
+options:
+ - Operation and maintenance manuals
+ - Startup and commissioning report
+ - As-built control sequence and balancing report
+ - Warranty documentation
+default: [Operation and maintenance manuals, Startup and commissioning report, As-built control sequence and balancing report, Warranty documentation]
+```
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following informational submittals:
+- Field test reports for airflow, heating output verification, and gas train leak test.
+- Manufacturer field representative report documenting startup attendance.
+- Coordination drawings reconciling the MAU with adjacent exhaust equipment, intake/discharge separation, and roof penetrations.
+
+```datasheet
+label: Informational submittals required
+type: checkbox
+options:
+ - Field test reports
+ - Manufacturer field representative report
+ - Coordination drawings
+default: [Field test reports, Coordination drawings]
+```
+
+# Quality Assurance {toc}
+
+## The MAU and its heat section shall bear the listing mark of a nationally recognized testing laboratory for the as-furnished configuration.
+
+## New equipment shall be listed under UL 60335-2-40; equipment carrying a UL 1995 mark is acceptable for in-service or field-verified units.
+
+## New equipment shall not be specified for new procurement under UL 1995.
+
+## UL 1995 was officially superseded by UL 60335-2-40 effective January 1, 2025. Both marks remain valid on equipment already in service, and many field-installed MAUs will carry the older mark for years. New purchasing should reference the current standard so that the as-furnished unit is listed under an active certification. {note}
+
+## Indirect gas-fired heat exchangers shall be listed under UL 795 or harmonized CSA equivalent.
+
+## The supply fan aerodynamic performance shall be rated in accordance with AMCA 210.
+
+## The manufacturer shall be regularly engaged in the production of makeup air units of the type and capacity specified.
+
+## The installing contractor shall provide a factory-trained manufacturer's representative to perform or witness startup. Direct and indirect gas-fired heat sections involve a combustion safety chain — proof of airflow, flame supervision, and high-limit cutout — whose initial setup determines safe operation. A manufacturer representative at startup verifies the burner sequence, modulation, and safety interlocks under live conditions rather than relying solely on factory test data. {note}
+
+# Environmental and Service Conditions {toc}
+
+## Outdoor air intakes shall be located a minimum of 10 ft horizontally from any exhaust outlet, plumbing vent, relief opening, or loading dock per ASHRAE 62.1-2022 Section 5.16.1.
+
+## Incorrectly located intakes recirculate exhaust contaminants directly back into the supply airstream and defeat the purpose of a dedicated outdoor air unit. Rooftop layouts frequently place a MAU intake near a grease or general exhaust fan because both serve the same space. Verify the 10 ft horizontal separation — and greater separation where the exhaust is hazardous or high-velocity — on the coordination drawing before the rooftop equipment arrangement is finalized. {note}
+
+## The unit casing and components shall be rated for the full outdoor design temperature range at the project location, including the ASHRAE 99% winter heating design dry-bulb and the 0.4% summer design condition.
+
+```datasheet
+label: Winter heating design dry-bulb (99%)
+type: range
+unit: °F
+min: -30
+max: 50
+step: 1
+default: 5
+```
+
+```datasheet
+label: Summer cooling design dry-bulb (0.4%)
+type: range
+unit: °F
+min: 80
+max: 120
+step: 1
+default: 95
+```
+
+```datasheet
+label: ASHRAE climate zone
+type: select
+options:
+ - 1A
+ - 2A
+ - 2B
+ - 3A
+ - 3B
+ - 3C
+ - 4A
+ - 4B
+ - 4C
+ - 5A
+ - 5B
+ - 6A
+ - 6B
+ - 7
+ - 8
+default: 4A
+```
+
+## Cooling sections exposed to freezing outdoor conditions shall be protected against coil freeze-up by drain-down, glycol circulation, or face-and-bypass arrangement as scheduled.
+
+## A unit that cycles off in winter while exposed to outdoor air is at risk of freezing a wet coil, because outdoor air can reach the coil through the de-energized fan section. Chilled-water and DX coils that see outdoor air require an explicit freeze strategy: drain-down or glycol on hydronic coils, and low-ambient controls or a positive-closure intake damper that closes on shutdown. Specify the strategy here rather than leaving it to the installing contractor to discover during the first cold snap. {note}
+
+# Configuration and Heating Source {toc}
+
+## The heating source shall be selected based on fuel availability, application restrictions, and energy cost, and shall be one of the types scheduled below.
+
+## Direct gas-fired units introduce all products of combustion into the airstream and approach 100% thermal efficiency, but are prohibited where ignitable concentrations of vapor or dust may be present. Direct gas-fired burners sit in the airstream and transfer nearly all of the fuel's energy to the supply air, which makes them the most efficient and most common choice for 100% outdoor-air kitchen makeup. They are not acceptable for spray-finishing or solvent-laden exhaust applications, where NFPA 33 effectively requires an indirect-fired or electric source because an open flame cannot share an airstream that may carry ignitable concentrations. {note}
+
+## Indirect gas-fired units isolate combustion products behind a heat exchanger and vent flue gas separately, at the cost of some efficiency. The indirect heat exchanger keeps flue gas out of the supply air, which is required for spray booths and preferred wherever combustion-product contact is unacceptable. Because the exchanger is a wear item subject to thermal cycling, access for inspection and cleaning is a design requirement, not an option. {note}
+
+## Direct gas-fired units shall not be selected for spray-finishing, paint-booth, or any exhaust application where ignitable vapor or dust concentrations may be present.
+
+## Indirect gas-fired units shall be furnished with hinged access doors on both sides of the heat exchanger to permit annual inspection and cleaning.
+
+```datasheet
+label: Heating source type
+type: radio
+options:
+ - Direct gas-fired
+ - Indirect gas-fired
+ - Hot-water coil
+ - Steam coil
+ - Electric resistance
+default: Direct gas-fired
+```
+
+```datasheet
+label: Natural gas supply pressure at unit
+type: range
+unit: in. w.c.
+min: 5
+max: 14
+step: 0.5
+default: 7
+```
+
+## The cooling section shall be selected based on climate zone and occupancy comfort requirement, and shall be one of the types scheduled below.
+
+## A heating-only MAU is the default for kitchen and many industrial replacement-air applications, where the supply air need only be neutral, not cooled. In a commercial kitchen the hood captures the cooking heat and the makeup air simply replaces the exhausted volume; cooling the makeup air below room temperature wastes energy and can disrupt hood capture. Cooling is added where occupant comfort in the served space depends on the supply temperature, or where the climate makes untempered 95 °F+ outdoor air unacceptable. {note}
+
+```datasheet
+label: Cooling section
+type: radio
+options:
+ - None (heating only)
+ - Direct-expansion (DX)
+ - Chilled-water coil
+ - Indirect evaporative
+ - Indirect-direct evaporative (two-stage)
+default: None (heating only)
+```
+
+```datasheet
+label: Mixing / recirculation arrangement
+type: radio
+options:
+ - 100% outdoor air (ASHRAE Cycle I)
+ - Modulating OA/RA damper (ASHRAE Cycle III)
+default: 100% outdoor air (ASHRAE Cycle I)
+```
+
+## Kitchen and laboratory makeup air shall be 100% outdoor air (ASHRAE Cycle I); recirculation is permitted only where the served occupancy and code allow return air to be mixed with outdoor air. Cycle I delivers all outdoor air with no recirculation and is the safe default for grease-laden, fume, or process exhaust where return air would carry contaminants. Cycle III modulates an outdoor/return damper to recover energy and is appropriate only for general occupancies where the exhausted air is clean enough to partly recirculate. {note}
+
+# Unit Location and Casing {toc}
+
+## The unit location shall be confirmed before casing material and weatherization are selected, because rooftop and indoor installations have different exposure requirements.
+
+```datasheet
+label: Unit location
+type: radio
+options:
+ - Rooftop (packaged)
+ - Indoor (mechanical room)
+default: Rooftop (packaged)
+```
+
+## Rooftop units shall be furnished with a fully weatherized, gasketed casing and a factory or field roof curb matched to the unit base.
+
+## Casing panels shall be double-wall construction with a minimum 1 in. insulating core to limit casing heat loss and surface condensation. Double-wall panels protect the insulation from airstream erosion and damage during service, and keep the interior surface above the dew point in conditioned sections. Single-wall casings are acceptable only on small heating-only units in benign indoor environments. {note}
+
+## Casing material shall be selected for the service environment; standard G90 galvanized steel is unacceptable in high-grease, high-moisture commercial kitchen environments.
+
+## Galvanized casing corrodes rapidly when continuously exposed to grease aerosol and the moisture of a commercial kitchen, leading to early casing failure and rust staining. For food-service makeup air, specify stainless-steel or epoxy/phenolic-coated casing for any surface exposed to grease-laden return paths or wash-down. The premium is small relative to replacing a corroded unit, and it preserves the unit's listing and appearance over its service life. {note}
+
+```datasheet
+label: Casing material
+type: select
+options:
+ - G90 galvanized steel
+ - Aluminum
+ - Stainless steel
+ - Epoxy/phenolic-coated steel
+default: G90 galvanized steel
+```
+
+```datasheet
+label: Casing panel construction
+type: radio
+options:
+ - Single-wall
+ - Double-wall, 1 in. insulating core
+ - Double-wall, 2 in. insulating core
+default: Double-wall, 1 in. insulating core
+```
+
+## Large rooftop units can weigh several thousand pounds, and the structural engineer of record shall confirm roof capacity and curb detailing before the unit is finalized.
+
+## A 10,000 CFM-class MAU can weigh between roughly 2,000 lb and 8,000 lb depending on heat and cooling sections, which often governs roof framing at the unit location. Coordinate the equipment weight, footprint, and support-point reactions with the structural engineer early. Discovering after order that the roof cannot carry the selected unit forces either a structural retrofit or a unit re-selection, both of which are far more costly than a coordination check during design. {note}
+
+# Airflow, Fan, and Static Pressure {toc}
+
+## The supply fan shall deliver the scheduled airflow at the scheduled external static pressure, rated per AMCA 210.
+
+## The makeup air supplied shall be a minimum of 85% to 90% of the total coincident exhaust the unit offsets, sized after totaling all exhaust fans served by the space.
+
+## Sizing makeup air below the exhaust it offsets is the most common and most damaging MAU error, producing sustained negative pressure that back-drafts gas appliances and makes doors hard to open. Before sizing, total every exhaust fan that draws on the served space — kitchen hoods, toilet exhaust, general and process exhaust — not just the hood being replaced. Undersizing leaves the building under persistent negative pressure, which back-drafts atmospheric gas appliances, slams or jams doors, whistles at every opening, and generates continuous occupant complaints. For commercial kitchens, NFPA 96 Section 8.3.1 is the controlling provision: replacement air must prevent negative pressure greater than 0.02 in. w.c. at the cooking equipment face, with 80% to 90% of hood exhaust volume a reasonable starting baseline. {note}
+
+```datasheet
+label: Scheduled supply airflow
+type: range
+unit: CFM
+min: 1000
+max: 150000
+step: 100
+default: 8000
+```
+
+```datasheet
+label: External static pressure
+type: range
+unit: in. w.g.
+min: 0.5
+max: 5.0
+step: 0.1
+default: 1.0
+```
+
+```datasheet
+label: Fan arrangement
+type: radio
+options:
+ - Supply only
+ - Supply and return/relief fan
+default: Supply only
+```
+
+## Any MAU serving a variable-volume exhaust system shall be furnished with a variable frequency drive and shall track the exhaust rate via a building static pressure signal.
+
+## A fixed-speed makeup air unit cannot follow a variable-speed exhaust hood, so the building pressure swings out of balance whenever the exhaust modulates. Demand-controlled kitchen ventilation and laboratory exhaust both vary their flow with load. If the MAU is single-speed, partial-load exhaust leaves the space over-pressurized and full-load exhaust leaves it under-pressurized. A VFD with a building static pressure reset keeps supply and exhaust matched across the full operating range, which is also the energy-efficient arrangement ASHRAE 90.1 favors. {note}
+
+```datasheet
+label: Supply fan speed control
+type: radio
+options:
+ - Single-speed
+ - Two-speed
+ - Variable frequency drive (VFD)
+default: Variable frequency drive (VFD)
+```
+
+## VFDs shall be furnished on supply fan motors larger than 1 HP except where a constant-volume application is documented, consistent with ASHRAE 90.1-2022 Section 6.5.3.1.
+
+## The discharge configuration shall be coordinated with the duct routing and available space and shall be one of the arrangements scheduled below.
+
+```datasheet
+label: Discharge configuration
+type: radio
+options:
+ - Horizontal (blow-through)
+ - Vertical down-discharge
+ - Plenum discharge
+default: Vertical down-discharge
+```
+
+# Heating and Cooling Capacity {toc}
+
+## The heating section shall be sized to raise the outdoor air from the winter heating design dry-bulb to the scheduled discharge air temperature setpoint at the scheduled airflow.
+
+## Heating capacity shall be computed as Q (BTU/hr) = 1.1 × CFM × ΔT (°F), where ΔT is the rise from the design outdoor temperature to the discharge setpoint. The 1.1 factor bundles the specific heat and density of standard air; at high altitude or extreme temperature the density correction should be applied explicitly. Size to the 99% winter design day so the unit can recover the space during the coldest expected operating hours without continuous high-fire operation. {note}
+
+```datasheet
+label: Discharge air temperature setpoint (heating)
+type: range
+unit: °F
+min: 55
+max: 75
+step: 1
+default: 65
+```
+
+## Unlisted direct gas-fired units shall not discharge air exceeding 150 °F; listed units shall observe their listed maximum discharge temperature. {note}
+
+## IMC limits the supply-air temperature differential at the space to within 10 °F of the occupied temperature where the resulting load would otherwise exceed the building HVAC capacity. A MAU discharging air far above or below room temperature dumps a load the zone HVAC must then absorb. Keeping the discharge close to neutral — or tempering toward room temperature — keeps the makeup air from overwhelming the comfort system, which is the IMC concern behind the differential limit. {note}
+
+## Where a cooling section is scheduled, the cooling coil shall deliver the scheduled leaving-air temperature at the summer design condition and scheduled airflow.
+
+```datasheet
+label: Cooling coil leaving air temperature
+type: range
+unit: °F
+min: 52
+max: 65
+step: 1
+default: 56
+```
+
+```datasheet
+label: Chilled-water entering water temperature
+type: range
+unit: °F
+min: 40
+max: 48
+step: 1
+default: 44
+```
+
+## Gas-fired heating sections shall be furnished with a discharge air high-limit cutout that de-energizes the gas valve on over-temperature, per UL 795 and NFPA 54.
+
+## Without a high-limit cutout, a gas valve that sticks open can discharge dangerously hot air into the occupied space or duct system. The high-limit control is the last line of defense in the combustion safety chain. It is required by the listing standard and the fuel gas code, and its setpoint and manual-reset behavior should be verified at startup rather than assumed from the factory configuration. {note}
+
+# Gas Train and Combustion {toc}
+
+## Gas-fired units shall be furnished with a factory-assembled, listed gas train sized for the scheduled input and supply pressure per NFPA 54.
+
+## The gas train shall include manual shutoff, pressure regulation, redundant safety shutoff valves, and flame supervision appropriate to the input rating.
+
+## NFPA 54 scales the required safety devices with input — larger burners require dual safety shutoff valves and proof-of-closure. The gas train is a listed assembly; field modification voids the listing, so any field-required changes must be made by the manufacturer or its authorized representative. {note}
+
+## Combustion air for indirect-fired sections shall be provided in accordance with NFPA 54.
+
+## Flue gas venting for indirect-fired sections shall be provided in accordance with NFPA 54.
+
+```datasheet
+label: Heating input (gas-fired)
+type: range
+unit: MBH
+min: 50
+max: 500
+step: 10
+default: 200
+```
+
+## The scheduled gas supply pressure shall be confirmed with the serving utility.
+
+## Large direct-fired units operating at high fire may require elevated gas supply pressure beyond standard service pressure; confirm adequate utility capacity before finalizing the gas train. {note}
+
+# Filtration {toc}
+
+## The unit shall be furnished with a pre-filter section sized for the full airflow and accessible for service without tools beyond a standard latch.
+
+## MERV-8 pre-filtration is the baseline for replacement air.
+
+## Laboratory and healthcare applications shall use MERV-13 minimum per the served space requirements.
+
+## The fan shall be selected for the dirty-filter static pressure condition.
+
+## Higher-efficiency filtration raises static pressure and is warranted where the served space has an indoor-air-quality requirement. The pre-filter protects the heat exchanger and coil and removes the coarse outdoor load. {note}
+
+```datasheet
+label: Pre-filter efficiency
+type: select
+options:
+ - MERV-8
+ - MERV-11
+ - MERV-13
+default: MERV-8
+```
+
+# Electrical {toc}
+
+## Electrical connections shall comply with NEC Articles 430 and 440; spray-booth applications shall additionally comply with Articles 500 through 516 for the classified location.
+
+## Supply fan motors shall be NEMA Premium efficiency (IE3) and compatible with the scheduled speed control.
+
+```datasheet
+label: Supply voltage / phase
+type: select
+options:
+ - 208V / 3Φ
+ - 230V / 3Φ
+ - 460V / 3Φ
+ - 575V / 3Φ
+default: 460V / 3Φ
+```
+
+```datasheet
+label: Supply fan motor size
+type: range
+unit: HP
+min: 1
+max: 75
+step: 0.5
+default: 7.5
+```
+
+# Controls and Interlock {toc}
+
+## The MAU shall be electrically interlocked with the exhaust system it serves so that it starts and stops with the exhaust, per NFPA 96 and the IMC.
+
+## A MAU that runs while its exhaust is off pressurizes and back-drafts the space, so the interlock is a code requirement, not a convenience. The interlock ties the makeup air to the exhaust it offsets. Omitting it allows the supply fan to run alone — over-pressurizing the building when hoods are off, or leaving exhaust unbalanced when the MAU trips — which defeats the pressure control the unit exists to provide. Wire the interlock so that loss of either side is annunciated. {note}
+
+## The controls strategy shall be one of the arrangements scheduled below and shall match the exhaust system it serves.
+
+```datasheet
+label: Controls strategy
+type: radio
+options:
+ - Constant-volume on/off interlock with exhaust
+ - Variable-volume building pressure tracking
+ - Full DDC / BAS integration
+default: Constant-volume on/off interlock with exhaust
+```
+
+## Discharge supply diffusers shall be located and oriented so that supply air does not blow directly into the hood capture zone or onto cooking equipment.
+
+## Supply air short-circuiting into the hood reduces capture efficiency and can extinguish pilot lights, defeating both the hood and the appliance. The makeup air must reach the space without blowing across the cooking surface or into the hood throat. Coordinate diffuser location, throw, and velocity with the kitchen hood design so the replacement air mixes into the room rather than being captured straight back out, which would short-circuit the entire ventilation system. {note}
+
+## Where a BAS is provided, the MAU control points shall be integrated for monitoring of supply airflow, discharge temperature, fan status, and alarm conditions.
+
+# Testing {toc}
+
+## The MAU shall be factory tested for airflow performance, heating output, controls function, and gas train integrity before shipment.
+
+## Factory testing shall include an airflow performance test per AMCA 210, a heating output verification, a controls checkout, and a gas train leak test.
+
+## The installed unit shall be field commissioned in accordance with ASHRAE Guideline 0-2019.
+
+## Field commissioning shall verify measured supply airflow, discharge air temperature across the operating range, exhaust interlock operation, and building pressure under all served exhaust modes.
+
+## Functional performance testing confirms the unit performs as designed in place, not just on the test floor. The interlock and pressure tests are the ones most likely to reveal a coordination gap — a missed exhaust fan in the makeup-air total, a reversed interlock, or a diffuser short-circuit — and should be witnessed. {note}
+
+## A gas train leak test shall be performed on gas-fired units before initial firing.
+
+## Measured building pressure at the served space shall confirm the design does not produce sustained negative pressure exceeding 0.02 in. w.c. at any cooking equipment face for kitchen applications.
+
+# Installation {toc}
+
+## The unit shall be installed level on its roof curb or structural support with continuous gasketing and flashing to prevent water intrusion.
+
+## Supply and return duct connections shall be made with flexible connectors.
+
+## Supply and return duct connections shall be constructed to the SMACNA duct pressure class matching the unit static pressure.
+
+## Service clearances shown on the approved shop drawings shall be maintained on all sides requiring access, including both heat-exchanger access doors on indirect-fired units.
+
+## Cooling sections shall be provided with a condensate drain pan, trap, and drain piping sized and trapped per IMC Section 307.2.
+
+## Negative-pressure draw-through cooling sections require a deep-seal condensate trap, or the negative pressure holds water in the pan until it overflows. A draw-through coil sits under negative pressure, which pulls water up the drain leg and prevents free drainage through an unsealed or shallow trap. Provide a trap with a seal depth at least equal to the unit's negative static pressure plus a margin (minimum 1 in. seal), so the pan drains continuously rather than filling until it spills into the unit. {note}
+
+## Outdoor air intakes shall be furnished with bird screen and, where exposed to weather-driven rain, an integral or hooded weather louver sized to limit water carryover.
+
+## The unit shall be set on vibration isolation appropriate to the fan size and structural support, coordinated with [[sync/electric-motors]] for the fan motor and drive selection. {note}
+
+# Delivery, Storage, and Handling {toc}
+
+## Units shall be delivered factory-crated with intake and discharge openings covered and gas train connections capped.
+
+## Units shall be stored level, off the ground, and protected from weather until installed; rooftop units shall not be set until the curb and roof are weathertight.
+
+## Lifting and rigging shall use the manufacturer's designated lifting points and shall not impose loads on the casing panels or gas train.
+
+# Warranty {toc}
+
+## The manufacturer shall warrant the complete unit against defects in materials and workmanship for a minimum of one year from startup or eighteen months from shipment, whichever occurs first.
+
+## The gas-fired heat exchanger shall carry an extended warranty appropriate to the heating source and application.
+
+```datasheet
+label: Unit warranty period
+type: select
+options:
+ - 1 year from startup
+ - 2 years from startup
+ - 5 years from startup
+default: 1 year from startup
+```
+
+```datasheet
+label: Heat exchanger warranty period
+type: select
+options:
+ - 5 years
+ - 10 years
+ - 15 years
+default: 10 years
+```
+
+# Spare Parts {toc}
+
+## The Contractor shall furnish one complete set of replacement filters of each type and size installed in the unit.
+
+## The Contractor shall furnish recommended spare ignition and flame-supervision components for gas-fired units as listed by the manufacturer.
+
+```datasheet
+label: Spare parts to be furnished
+type: checkbox
+options:
+ - One complete set of replacement filters
+ - Spare ignitor / flame sensor
+ - Spare fan belts (belt-drive units)
+ - Spare gas valve
+default: [One complete set of replacement filters, Spare ignitor / flame sensor]
+```