Make-Up Air in Phoenix Restaurants: The Problem Behind the Front Door
If your front door is hard to open and the dining room is never comfortable, you probably have a building pressure problem rather than an HVAC capacity problem.
Commercial kitchen exhaust hoods remove large volumes of air, and that air must be replaced by a make-up air system. When make-up air is undersized or not working, the building goes negative — doors become hard to open, outside air infiltrates through every gap, the dining room never holds temperature, and the hood stops capturing smoke properly.
What negative pressure feels like
Staff usually describe the symptoms without knowing they are related: the front door is heavy to open or slams shut, there is a whistle around the door frame, the dining room near the entrance is hot in summer and cold in winter, the kitchen is smoky even with the hood running, and the HVAC runs constantly without ever getting comfortable.
All of those are one problem. The exhaust hood is pulling more air out of the building than the make-up air system is putting back, so the building is at negative pressure relative to outside — and outside air is being pulled in through every gap available, including the front door and the space around it.
The arithmetic
A commercial kitchen hood can exhaust a very large volume of air, and in a busy kitchen it runs continuously during service. That air has to come from somewhere.
A properly designed make-up air unit supplies most of that volume as tempered outside air, delivered near the hood. The remainder comes from the building's HVAC outside air intake, which balances the space.
When the make-up air unit is undersized, broken, or turned off — which happens constantly, because staff find it noisy or drafty — the building makes up the difference through infiltration. In Phoenix that means 110-degree outside air in summer being pulled into a space you are trying to cool to 72.
Why it matters beyond comfort
- Hood capture fails. A hood needs the right airflow pattern to capture smoke and grease. Negative building pressure disrupts it, so smoke rolls out into the kitchen.
- Cooling and heating costs climb sharply. Uncontrolled infiltration is the most expensive possible way to bring in outside air.
- Doors become a safety issue. Exit doors that are hard to open are a genuine code and life-safety problem.
- Gas appliance backdrafting. In severe cases, negative pressure can pull combustion products back down a flue. That is a carbon monoxide risk.
- Dust and odor infiltration. Air pulled in through gaps is unfiltered.
What we check
Diagnosing this is measurement work, not guesswork. We check building pressure relative to outside, verify the make-up air unit is actually running and its damper is opening, confirm the exhaust and make-up volumes are in reasonable balance, and verify the interlock — the control that starts make-up air whenever the hood runs.
A broken interlock is common and easy to miss. The hood runs, the make-up air unit does not, and nobody notices because the hood is doing its visible job.
The Phoenix-specific complication
Make-up air in a temperate climate can often be untempered — just outside air brought in near the hood. In Phoenix, bringing in 110-degree air untempered makes the kitchen unbearable, so make-up air units here generally need evaporative or mechanical cooling.
Evaporative cooling works very well for this application during our dry months and poorly during monsoon, which is why many Valley restaurants have a make-up air system that works beautifully in May and struggles in August. That is a design reality worth understanding before assuming something is broken.
What it costs to ignore
A restaurant fighting negative pressure is paying for it three times: in energy, in an HVAC system running continuously and wearing out early, and in a dining room experience that keeps customers from staying for dessert.
It is also one of the more fixable commercial HVAC problems. Frequently the make-up air unit is present and simply not working, not interlocked, or turned off — which is a repair rather than a capital project.
Frequently asked
Why is my restaurant front door hard to open?
Almost always negative building pressure. The kitchen exhaust hood is removing more air than the make-up air system is replacing, so the building pulls air in through every available gap — including around the door, which is what makes it heavy.
What is a make-up air unit?
A system that supplies outside air to replace the large volume removed by a commercial kitchen exhaust hood. In Phoenix it generally needs to temper that air — evaporative or mechanical cooling — because bringing in 110-degree air untempered makes the kitchen unworkable.
Can negative pressure cause a carbon monoxide problem?
In severe cases, yes. Strong negative pressure can pull combustion products back down the flue of a gas appliance instead of letting them vent. That is one of several reasons building pressure is a safety issue, not just a comfort one.