Skip to main content
Back to Glossary
Mechanical / HVACaka: MAUaka: supply air unitaka: dedicated outdoor air system

Makeup Air Unit

In Plain English

A unit that brings in and conditions fresh outdoor air to replace air being exhausted from a building.

Definition

A dedicated air handling unit that supplies conditioned outdoor air to replace air exhausted from a building or space. Makeup air units are required when large exhaust systems—such as kitchen hoods or laboratory fume hoods—create negative pressure that could cause combustion appliance backdrafting or occupant discomfort. They typically include heating and sometimes cooling and humidity control.

Why It Matters in Bidding

Makeup air units are a significant cost driver on projects with large exhaust loads, and they are frequently triggered by code-required pressure balancing that less experienced estimators overlook until plan review. Because MAU sizing, gas or electric heat, controls interlocks with exhaust hoods, and rooftop structural support all affect price, missing or undersizing the unit can blow the mechanical budget and stall award.

Example

Bidding a restaurant build-out, the mechanical estimator sizes a gas-fired makeup air unit to match the Type I kitchen hood exhaust CFM and adds a line for the roof curb, gas piping, and hood-MAU control interlock.

Related Terms

Exhaust FanAir HandlerDuctworkHVAC

Frequently Asked Questions

Typically when large exhaust systems—commercial kitchen hoods, fume hoods, or paint booths—would otherwise create negative building pressure causing backdrafting or door issues. Code and the mechanical engineer's design dictate the requirement. Estimators should scan the drawings for high-CFM exhaust and confirm whether a dedicated MAU is specified before pricing the HVAC scope.
Beyond the unit itself, include the roof curb or structural support, ductwork and diffusers, gas or electric heating connections, controls and the exhaust-fan interlock, electrical power, and any required outside-air dampers. Crane or rigging for rooftop placement and roofing penetration flashing are also commonly missed line items on MAU takeoffs.
Sizing follows the exhaust CFM it must replace plus the heating capacity needed to temper outdoor air to design conditions, which varies sharply by climate. Larger CFM and colder design temperatures increase unit cost, gas load, and electrical demand. Estimators should price the scheduled unit rather than assuming, since substitutions can affect responsiveness.

Need more than definitions?

Get AI-powered bid alerts, automated form filling, and proposal drafting.

Start Free Trial

© 2026 ConstructionBids.ai — A LaderaLabs Product