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Commercial · Kitchen VentilationMake-Up Air Units for Restaurants & Kitchens
A make-up air unit replaces the air your kitchen hood throws outside. Size it right and the hood captures smoke, the doors open normally and the dining room stays warm; size it wrong, or leave it broken, and the whole building goes negative and starts pulling air down every flue it can find.
Every commercial kitchen exhaust hood is a hole in the building. A single 3,000 CFM hood over a char-broiler moves the volume of a small restaurant out the roof every few minutes, and that air has to come back in from somewhere. Without a working make-up air unit it comes in under the front door, around the walk-in seals, and — the dangerous one — backwards down the flue of the water heater or the make-up air unit's own burner. The symptoms operators describe are always the same: a front door that takes two hands, a hood that spills smoke over the front lip, and a dining room that is cold in January no matter what the thermostat says.
The unit itself is usually a gas-fired rooftop or wall-mounted cabinet with a blower, a filter bank and a burner that tempers incoming air on cold days. Direct-fired units put the flame straight in the airstream, so nearly all of the burner's heat ends up in the air rather than going up a flue — which is why they are the usual choice for lifting −15°C outdoor air to something a kitchen can live with. Indirect-fired units use a heat exchanger and a separate vent, and are chosen where the discharge cannot carry any combustion products. Both are TSSA gas appliances, and both have to be interlocked with the exhaust fan so the make-up air runs whenever the hood runs — that interlock is the first thing we check on a service call, because someone has almost always bypassed it.
Balance is the part that gets missed. The kitchen should stay slightly negative relative to the dining room so odours do not migrate, which usually means supplying somewhat less than the hood exhausts and letting the rest transfer in through the building's other supply air. We measure at the hood face rather than trusting the nameplate, because a decade of grease has changed both the exhaust fan's output and the make-up air unit's filter loading. A correctly sized make-up air unit balances the hood instead of fighting it.
We work on kitchens across the Hamilton restaurant strips, Burlington's Brant Street, and Kerr Village and Old Oakville, and new installs are permit work through the City of Hamilton or Halton Region building department. More on the rest of the equipment in a commercial kitchen is on our restaurant HVAC page, and the wider scope sits under commercial HVAC — or call the shop and describe what the hood is doing.
Your kitchen needs make-up air attention when
- The hood spills smoke into the kitchen instead of capturing it at the front edge
- Exterior doors are hard to pull open, or whistle and slam when the exhaust fan starts
- Pilot lights blow out, or the water heater and boiler back-draft when the line is running
- The dining room is cold and drafty in winter while the kitchen is uncomfortably hot
- The make-up air unit runs unheated because the burner has locked out and nobody reset it
How it works
We read exhaust volume at the hood, check whether the interlock still works, and find out how much supply air the building is actually delivering — not what the drawings say.
Unit sized to the corrected exhaust rate, curb or wall opening prepared, gas piped and pressure-tested, electrical and hood interlock wired, then commissioned at full fire with the discharge temperature verified.
Filter changes, belt tension, burner and flame-safeguard testing, and a re-balance after any hood or equipment change. Grease-laden kitchens are hard on filters, so the service interval is shorter than a rooftop unit's.
Brands: We service gas-fired make-up air units, kitchen exhaust fans and the packaged rooftop equipment that usually sits beside them, whatever the badge on the cabinet.
Common questions
Do I legally need a make-up air unit for a commercial hood?
In practice, yes — a Type 1 kitchen exhaust hood has to be paired with a source of replacement air, and building departments look for it at inspection. The exact requirement comes from the mechanical section of the building code and the hood's own listing, so we confirm it against your drawings and hood schedule rather than quoting a rule from memory.
Direct-fired or indirect-fired?
Direct-fired is the common choice for a kitchen: cheaper to buy, far more efficient at heating very cold outdoor air, and acceptable because the air is being exhausted continuously. Indirect-fired is chosen when the make-up air is being distributed beyond the kitchen or where the owner wants no combustion products in the supply stream at all.
Why is my make-up air unit blowing cold air in winter?
Usually the burner has locked out on a flame-safeguard fault, a dirty flame rod or a pressure switch, and the blower keeps running because it is interlocked to the hood. It is a repair, not a design problem — but running a kitchen on unheated −10°C air will freeze a wet line and drive staff off the cook line, so it gets treated as urgent.
Can you service a unit somebody else installed?
Yes. Most of what we see is inherited equipment on a roof that has not been opened in years. We test the burner and safeties, check the interlock, replace filters and belts, and give you a written condition report with what should be fixed now and what can wait.
Does this tie into my rooftop units?
It should. The make-up air unit, the hood exhaust and the rooftop units serving the dining room all share one building pressure, so changing one changes the others. We look at the set as a system when we balance it.