A make-up air unit (MAU) replaces the air that commercial kitchen exhaust hoods pull out of a building. Without one, your kitchen operates under negative pressure: exhaust fans can’t pull properly, combustion appliances backdraft, and conditioned air from the rest of the building gets sucked into the kitchen. In Michigan, where outdoor temperatures routinely fall below zero in winter, a make-up air unit also tempers the incoming air so it doesn’t shock staff or destabilize kitchen temperatures.
What a Make-Up Air Unit Actually Does
Every commercial exhaust hood removes air from the building, typically between 1,000 and 5,000 CFM depending on the size of the kitchen and the type of cooking equipment underneath it. That air has to come from somewhere. If there’s no dedicated make-up air system, the building tries to find its own air path: through gaps around doors, through HVAC return systems, or through gaps in the building envelope.
A properly designed make-up air unit solves this by introducing outdoor air directly at or near the hood, in a controlled volume and at a conditioned temperature. Most commercial MAUs temper the incoming air, meaning they heat it in winter so you’re not dumping 10-degree air at high velocity into a kitchen where staff are working and food is being prepared. Some units also cool incoming air in summer, though in Michigan’s climate, heating capacity is the primary concern.
The result is a kitchen that operates at or near neutral pressure: exhaust hoods pull correctly, combustion appliances draft properly, and the dining room isn’t drawing cold air in every time a kitchen door opens.
Why Michigan’s Climate Makes This Especially Important
In warmer climates, some kitchens can get by with minimal make-up air for part of the year. In Southeast Michigan, that’s not a realistic option. Here’s why:
- Winter air is dense. Cold, heavy air creates stronger pressure differentials between inside and outside. Without a MAU, your kitchen may experience significant negative pressure during Michigan winters, pulling cold air through every gap in the building and making it nearly impossible for hood fans to operate at rated capacity.
- Gas appliance backdrafting is a safety hazard. Negative pressure can cause gas ranges, ovens, and fryers to backdraft, pulling combustion gases back into the kitchen instead of exhausting them through the flue. This is a carbon monoxide risk. Michigan’s cold winters, which create extreme pressure differentials, make backdrafting more likely in kitchens without adequate make-up air.
- Untempered air is uncomfortable and damaging. Introducing large volumes of unheated outdoor air in January creates a miserable working environment and can cause condensation on cold surfaces, damage finishes, and trigger temperature controller issues in refrigerated equipment.
- HVAC system strain: Without make-up air, dining room HVAC systems compensate for the negative pressure by working harder, driving up energy costs and accelerating wear.
Code Compliance in Michigan
Michigan follows the Michigan Building Code and the Michigan Mechanical Code, both of which align closely with the International Mechanical Code (IMC). The IMC requires that kitchens with Type I hoods have a make-up air system that supplies at least 80 percent of the air exhausted by the hood system. Local jurisdictions in Wayne, Oakland, and Macomb counties may have additional requirements or specific inspection procedures.
New restaurant construction and major remodels require make-up air as part of the mechanical permit. However, many existing kitchens in Metro Detroit, particularly those that were built or last renovated before stricter enforcement, are operating without adequate make-up air. If your hood system is undersized or your kitchen runs under noticeable negative pressure, a code compliance issue may already exist.
Signs Your Make-Up Air Unit Needs Service
MAUs are relatively simple systems, but they do require maintenance. Watch for these signs that something is wrong:
- Kitchen feels noticeably negative, doors are hard to open from inside, or you can feel cold air rushing in around door frames
- Hood fans seem weaker than normal or grease buildup in the duct has increased
- Gas appliances have yellow or lazy flames, or pilot lights are blowing out
- The MAU fan is running but you can’t feel airflow at the supply diffuser
- The unit is making noise it didn’t make before (belt wear, bearing failure, or debris in the fan housing)
- The heating element or gas burner in the MAU is not tempering air in cold weather
SAMCO FM’s Experience with Make-Up Air Systems
SAMCO FM has been installing, servicing, and replacing make-up air units at commercial kitchens throughout Metro Detroit and Southeast Michigan since 1997. Our team brings 90+ years of combined experience across HVAC and kitchen ventilation systems. We work with gas-fired and electric MAUs across all major equipment configurations, from simple direct-fired tempering units to fully integrated supply fan and heating systems tied into building automation.
We can evaluate whether your existing make-up air system is sized correctly for your exhaust load, diagnose mechanical failures, and handle permit-required installations for new or remodeled kitchens.
When to Call a Professional
If you’re not sure whether your kitchen has an adequate make-up air system, or if you’ve noticed any of the signs above, call SAMCO FM for an assessment. Ignoring make-up air problems doesn’t just affect comfort, it creates fire, safety, and code compliance exposure that can close a kitchen.
Reach us at (734) 838-6300, email service@samcofm.com, or schedule a site assessment through samcofm.com. We serve commercial kitchen operators across Wayne, Oakland, Macomb, and Washtenaw counties.
Frequently Asked Questions
Do I need a make-up air unit if I already have an exhaust hood?
Yes. The exhaust hood removes air from the building. That air must be replaced. If there is no dedicated make-up air system, the kitchen will run under negative pressure. In Michigan, this almost always causes operational and code compliance problems, particularly in winter when pressure differentials between inside and outside are greatest.
How is a make-up air unit different from a regular HVAC unit?
A standard HVAC unit recirculates building air and conditions it. A make-up air unit brings in 100 percent outdoor air and tempers it before delivering it to the kitchen. They serve different functions. Some facilities use a combination of both: a MAU to replace exhaust air and an HVAC system to manage temperature in dining and common areas. They should be balanced together, not treated as interchangeable.
How much does a commercial make-up air unit cost to install in Michigan?
Installed costs vary depending on unit capacity, whether the system is gas-fired or electric, ductwork requirements, and permit complexity. Small direct-fired units for a single-hood kitchen can run $5,000 to $10,000 installed. Larger, multi-hood configurations with complex ductwork can run significantly higher. A site assessment from SAMCO FM will give you an accurate estimate based on your specific equipment and kitchen layout.
How often does a make-up air unit need to be serviced?
At minimum, twice a year, before the heating season and before summer. For high-volume kitchens, quarterly is better. PM visits should include belt and bearing inspection, burner cleaning and adjustment on gas-fired units, filter replacement, airflow verification, and controls check. A MAU that hasn’t been serviced in 2 or more years is likely underperforming.
