Make-up air unit service — the equipment that keeps your kitchen, your hood, and your dining room all working at once.

A make-up air (MUA) unit replaces the air that commercial kitchen exhaust hoods pull out of a building. A Type I hood over a cookline can exhaust 3,000 to 8,000 CFM. If that air is not "made up" by a dedicated unit, the building goes into negative pressure — exterior doors get hard to open, back-drafting pulls combustion gases down the water-heater flue, the hood stops capturing smoke and grease at the source, and the dining room gets pulled cold in winter. Mechanical codes (IMC 508 and NFPA 96) require make-up air to be provided wherever exhaust is installed. The MUA is what keeps the kitchen, the dining room, and the exhaust system all working together.

A direct-fired MUA passes the incoming outdoor air directly across an open gas burner — roughly 92% thermal efficiency, products of combustion enter the airstream, and it is approved for kitchen make-up air where the air is exhausted, not recirculated. An indirect-fired MUA heats a sealed heat exchanger and the combustion byproducts are vented separately through a flue — lower efficiency (around 80%) but the supply air never touches combustion gases, which is required when the make-up air is delivered into occupied space rather than dumped at the hood. Choosing wrong is one of the most common spec errors we find on existing Birmingham installations. We verify the application before recommending a replacement burner platform.

Almost always, yes. Doors that suck shut, whistling gaps around windows, a hood that lets smoke roll out into the dining room, and a pilot light or water heater that keeps blowing out are the classic symptoms of a building running under negative pressure because the make-up air unit has failed, was undersized, or was never balanced to the exhaust. We measure building static pressure, total exhaust CFM, and MUA supply CFM, then rebalance the system. In Birmingham restaurants this is one of the most common — and most misdiagnosed — service calls we take.

Quarterly for any MUA tied to a commercial kitchen running daily service. The gas train, burner, and combustion need annual analysis at minimum, but the intake filters and the exhaust/MUA balance drift faster than that in a grease-laden kitchen environment. We inspect the direct-fired burner profile or indirect heat exchanger, verify the gas pressure and combustion (CO/CO₂), check the intake damper and actuator, replace the intake filter bank, confirm the interlock between the MUA and the exhaust fans, and re-measure building static pressure on every visit.

Yes — balancing is the core of the job. A make-up air unit is only correct relative to the exhaust it serves. We measure total Type I and Type II hood exhaust CFM, set MUA supply to leave the building at a slight, code-appropriate negative pressure (so odors stay in the kitchen, not the dining room), and verify the electrical interlock so the MUA can never run without the exhaust or leave the exhaust running with no make-up air. NFPA 96 governs the exhaust side; we coordinate the MUA side so the whole system is correct.

We service Captive-Aire, Greenheck, RuppAir, Reznor, Modine, Cambridge Engineering, Trane, and AAON make-up air platforms — both direct-fired and indirect-fired, and the packaged "heat-and-cool" MUA units increasingly used on Birmingham restaurants that want tempered supply air year-round. We also service the dedicated outdoor air systems (DOAS) used on offices and schools for ASHRAE 62.1 ventilation, which are mechanically close cousins of kitchen make-up air.