Kitchen Exhaust Hood Airflow and Make-Up Air

By Commercial Service Company · October 9, 2026

If the front door to your restaurant suddenly takes two hands to pull open, or the pilot light on your range keeps dying for no obvious reason, the problem usually isn't the door hinge or a bad thermocouple. It's airflow. Your commercial kitchen exhaust hood is pulling air out of the building faster than it's being replaced, and the building is fighting back.

What Negative Pressure Actually Is

Every exhaust hood over a cookline removes a large volume of air, grease-laden smoke, and heat from the kitchen and sends it outside. That air has to be replaced from somewhere. If it isn't replaced on purpose, through a properly designed make-up air system, the building pulls it in wherever it can: through door gaps, window seams, cracked slabs, and gas appliance flues. When exhaust volume outpaces incoming air, the kitchen and often the whole building drops below outside pressure. That's negative pressure, and it shows up in some very practical, very annoying ways.

Doors That Won't Open, or Won't Stay Shut

One of the clearest signs of a negative-pressure building is a front or back door that suddenly feels heavy, slams on its own, or won't budge until someone yanks hard. The building is trying to equalize pressure by pulling air in through that doorway, and the door itself becomes part of the air path. In severe cases, exterior doors can be difficult or even unsafe to open quickly, which matters for fire exits and ADA compliance, not just customer convenience.

If this only happens when the exhaust hood and cooking equipment are running, that's a strong clue the hood system is out of balance rather than a hardware or closer adjustment issue.

Pilot Lights and Gas Appliances Blowing Out

Pilot lights are small, low-pressure flames, and they're sensitive to drafts. When negative pressure pulls air backward through a flue or combustion chamber, or creates a stronger-than-normal draft across an open burner, pilots can blow out repeatedly. Worse, severe negative pressure can cause flue gases from water heaters, ovens, or other gas appliances to spill back into the building instead of venting outside, which is a carbon monoxide and life-safety concern.

• Pilot lights that go out only when the hood or exhaust fans are running
• A gas appliance that seems to need relighting far more often than it used to
• Any sign of soot, discoloration, or odor near a flue or vent connection

Any of these involving gas appliances, venting, or combustion air is a job for a licensed gas technician. Do not attempt to adjust gas valves, pilot assemblies, or venting yourself. This is a safety issue, not a maintenance shortcut.

Make-Up Air: The Other Half of the System

A properly designed hood system isn't just an exhaust fan over the cookline. It's paired with a make-up air unit that introduces tempered outside air back into the kitchen to replace what the hood removes, keeping the building at or near neutral pressure. When that make-up air unit is undersized, shut off, not running on the same schedule as the exhaust fan, or simply out of service, the building has no way to stay balanced and negative pressure sets in fast.

In older buildings or kitchens that have added equipment over the years, it's common for exhaust capacity to grow while make-up air capacity stays the same. The hood system that worked fine when the kitchen was smaller can fall out of balance once you've added a second fryer bank or a larger charbroiler.

What You Can Check Before Calling

A few things an owner or manager can reasonably observe, without touching any gas, electrical, or refrigerant components:

• Does the door or pilot problem only happen when exhaust fans are running?
• Is the make-up air unit's fan actually running when the exhaust hood is on?
• Are supply air grilles or diffusers near the kitchen blocked, closed, or covered?
• Has new cooking equipment been added since the hood system was last balanced?

These observations help a technician diagnose the issue faster, but balancing airflow, adjusting dampers, and servicing make-up air units is skilled work best left to a qualified technician.

Why This Isn't Something to Ignore

Beyond the nuisance of heavy doors and relighting pilots all day, chronic negative pressure drives up utility costs, stresses HVAC equipment, and in the worst cases creates a real combustion-safety hazard with gas appliances. It's worth having the system checked rather than living with the symptoms.

If your exhaust hood and make-up air system seem out of balance, or you're dealing with doors that won't open or pilots that won't stay lit, Commercial Service Company has served restaurants, grocery stores, and commercial kitchens across Conway, Little Rock, Benton, Bryant, Maumelle, Jacksonville, Searcy, and Russellville since 1976. Give us a call at 501-548-2374 and we'll get a technician out to take a look.