Why Your Restaurant Kitchen Is Freezing and the Doors Are Hard to Open

The symptom list every operator recognises

Entry doors that are genuinely hard to pull open, or that whistle around the frame. A hood that no longer captures at the cookline, so smoke rolls into the kitchen and the dining room smells of the fryer. Pilot lights that blow out. A water heater or boiler that smells of exhaust or backdrafts. A dining room that will not hold temperature no matter what the rooftop unit does. And in January, a kitchen that is simply miserable to work in.

Those are not separate problems. They are one problem — the building is strongly negative relative to outdoors — and make-up air is almost always the cause.

The mechanism is simple. The hood removes air whether or not anything replaces it. If the make-up air unit is not delivering, the building finds that air wherever it can: around doors, through window frames, down flues, through every gap in the envelope. In a Twin Ports winter, that is −15°F air arriving continuously.

Why the dining room cannot be heated

This one confuses people, and it gets misdiagnosed as an undersized rooftop unit more often than anything else we see in restaurants.

If the kitchen is pulling thousands of CFM of subzero outdoor air into the building because make-up air is not working, that air has to be heated by something. Some of it is heated by your dining-room rooftop unit, which is now fighting a continuous stream of outdoor air it was never sized for. The unit runs constantly and the space still does not hold temperature.

Installing a bigger rooftop unit does not fix it. You would be paying to heat outdoor air that keeps arriving. Balancing the building is what fixes it, and it is usually cheaper than the equipment upgrade that was quoted instead.

The backdrafting side is the safety issue. A strongly negative building can pull exhaust back down the flue of a water heater or boiler, putting carbon monoxide into the space where your staff work. That is not a comfort complaint, and it needs worst-case testing with all the exhaust equipment running.

What fixing it involves

Measurement first, always. Actual exhaust airflow at the hood, actual supply airflow at the make-up air unit, and the pressure relationship of the kitchen to the dining room and to outdoors — measured with the doors closed and the kitchen in its real operating state, not idle.

Then the interlock. The make-up air unit must run whenever the hood runs. A failed or never-wired interlock is one of the most common findings, and it produces exactly the symptoms above even when there is a perfectly good MUA sitting on the roof.

Then balance. The goal is the kitchen slightly negative relative to the dining room, so cooking odours do not migrate — but only slightly negative relative to outdoors, not the strong negative that causes every problem here. That is a setting achieved by measurement, not by assumption.

A surprising number of chronic restaurant complaints resolve at this stage without new equipment. A kitchen with a brand-new make-up air unit can still have every symptom if the unit was installed and never balanced, and that is a common story.