Your makeup air unit (MAU) is one of the most important — and most neglected — pieces of equipment on your roof. When it stops working, the problems show up everywhere: the kitchen is freezing in winter, doors are impossible to open, pilot lights blow out, and your gas bill doubles. Most restaurant owners don't even know they have one.
What Does a Makeup Air Unit Do?
Your kitchen exhaust hood pulls thousands of cubic feet of air out of the building every minute. That air has to come from somewhere. The MAU is designed to replace about 80% of the exhausted air with tempered (heated or cooled) outside air, delivered directly into the kitchen.
Without the MAU, your building goes under severe negative pressure. The exhaust is still pulling air out, so the building sucks in raw outside air through every crack, door, window, and gap. In January in New Jersey, that's 35°F air pouring in. In August, it's 95°F humid air.
Your building HVAC — the furnace in winter, the AC in summer — has to condition all of that infiltrating air. That's energy you're paying for that the MAU should be handling.
Signs Your MAU Isn't Working
- Kitchen is freezing in winter even though the heat is running
- Front door is extremely hard to open (severe negative pressure pulling it shut)
- Pilot lights on gas equipment blow out randomly
- Whistling sounds from doors, windows, or gaps
- Energy bills significantly higher than similar restaurants
- Kitchen is uncomfortable — staff complaining about temperature
- Hood capture is poor — smoke escaping even though the exhaust fan is running
Common MAU Problems
Burner Not Igniting Gas-fired MAUs heat the incoming air with a burner section. If the burner fails, the unit blows cold outside air directly into the kitchen — or the safety controls shut the unit off entirely. Common causes: failed igniter, gas valve issue, flame sensor dirty, or gas supply interrupted.
Frozen Coils In cold weather, condensation freezes on the coils and blocks airflow. The MAU either stops moving air or moves it at drastically reduced volume. Usually caused by a failed defrost cycle or a refrigerant issue on units with cooling capability.
Belt or Motor Failure Same as exhaust fans — MAU supply fans use belts and motors that wear out. When the belt breaks, no air moves. When the motor fails, same result.
Filter Clogged MAU intake filters get clogged with dirt, pollen, and debris. A severely clogged filter starves the unit for air, reducing supply volume drastically. This is the easiest fix — change the filter. Most MAUs need filter changes every 1-3 months.
Controls Failure The MAU's control board, thermostat, or interlock with the exhaust system fails. The unit either won't turn on, won't modulate properly, or doesn't sync with the exhaust hood.
What It Costs You When the MAU Is Down
For a typical 10-foot hood exhausting 2,750 CFM, the MAU is designed to supply about 2,200 CFM of tempered air. When the MAU is completely down:
- 2,200 CFM of raw outside air infiltrates through doors and gaps
- Heating waste (winter): approximately $4,200/year in extra gas
- Cooling waste (summer): approximately $1,060/year in extra electricity
- Total: over $5,200/year in wasted energy — on top of the repair cost
The MAU repair is a fraction of the annual energy waste. The math is clear — contact us for a quote.
What to Check Before You Call
1. Filters — pull them out and check. If they're solid gray/brown, replace them.
2. Breaker — check the electrical panel for a tripped breaker.
3. Gas supply — is the gas valve open? Did someone shut it off?
4. Interlock — many MAUs are interlocked with the exhaust fan. If the exhaust fan is off, the MAU won't run.
5. Thermostat — check the setting. It may have been changed or malfunctioned.
True Commercial Service repairs and maintains all brands of makeup air units across Union County, NJ. If your MAU is down, your kitchen is losing money every hour. Call us for same-day service.
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