Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Makeup Air Units
…46 unchanged lines
## 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−## Where a referenced standard has been superseded by the authority having jurisdiction, the currently adopted edition shall apply.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}
+## Where a referenced standard has been superseded by the authority having jurisdiction, the currently adopted edition shall apply.
| Standard | Title |
…93 unchanged lines
## 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}
+## 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.
# Environmental and Service Conditions {toc}
…87 unchanged lines
## 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
…8 unchanged lines
```
+## 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}
+
+## The mixing and recirculation arrangement shall be specified based on whether the served space requires tempered or comfort-conditioned supply air.
+
```datasheet
label: Mixing / recirculation arrangement
…22 unchanged lines
## 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 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.
+```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
+```
+
## 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
…7 unchanged lines
```
−```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
−```
+## 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}
## 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.
…5 unchanged lines
## 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
…16 unchanged lines
```
−```datasheet
−label: Fan arrangement
−type: radio
−options:
− - Supply only
− - Supply and return/relief fan
−default: Supply only
−```
+## 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}
+
## 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
…6 unchanged lines
```
+## 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}
+
## 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.
…10 unchanged lines
```
+```datasheet
+label: Fan arrangement
+type: radio
+options:
+ - Supply only
+ - Supply and return/relief fan
+default: Supply only
+```
+
# 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}
+## 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.
```datasheet
…7 unchanged lines
```
−## Unlisted direct gas-fired units shall not discharge air exceeding 150 °F; listed units shall observe their listed maximum discharge temperature. {note}
+## Unlisted direct gas-fired units shall not discharge air exceeding 150 °F; listed units shall observe their listed maximum discharge temperature.
## 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}
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## 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
…6 unchanged lines
```
+## 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}
+
# Electrical {toc}
…79 unchanged lines
## 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}
+## 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.
# Delivery, Storage, and Handling {toc}
…47 unchanged lines
default: [One complete set of replacement filters, Spare ignitor / flame sensor]
```