Why Is Your Kitchen Exhaust Hood Not Pulling Smoke and Grease Like It Should?
If your hood used to clear smoke and grease fine and now it doesn't, the first thing most people check is the hood itself. Filters, fan, ductwork. Sometimes that's the answer. Often it isn't.
A hood that's running but not pulling right is usually starved for air, not broken. Your exhaust fan can be spinning at full speed and still fail to clear smoke if there isn't enough air coming back into the kitchen to replace what it's pulling out. That's a makeup air problem, and it's one of the most common things missing in older restaurant buildouts and conversions across Chicago.
Here's how to tell the difference, and what's actually happening in your kitchen.
What Is Makeup Air, and Why Does Your Hood Need It?
Your exhaust hood's job is to pull air, smoke, and grease-laden vapor out of the kitchen and push it outside. Every cubic foot of air that leaves through that hood has to be replaced by a cubic foot of air coming back in. That replacement air is makeup air.
When a kitchen doesn't have a dedicated makeup air system, or the one it has isn't sized correctly for the hood, the kitchen runs at negative pressure. The exhaust fan is still trying to pull the same volume of air, but there isn't enough air available to take its place. The result is a hood that looks like it's working but doesn't actually clear the air the way it should.
This isn't a defect in the hood or the fan. It's a building system problem, and it shows up most often in spaces that were converted into restaurants from something else, or in older Chicago buildings where the original ventilation wasn't designed around a commercial kitchen exhaust load.
Signs Your Kitchen Is Running Without Enough Makeup Air
A negative pressure kitchen has a specific set of symptoms, and most of them get blamed on something else first.
Exterior doors are hard to open, or slam shut on their own. The building is trying to pull in air from anywhere it can find it.
Smoke and grease haze lingers near the hood even with the fan running, instead of clearing the way it used to.
Pilot lights flicker or blow out on gas equipment, because the burners are competing for the same limited air supply.
The kitchen feels hotter or more humid than it should, even with the HVAC running, because conditioned air from the dining room or elsewhere in the building is getting pulled into the kitchen to make up the deficit.
A back door near the kitchen whistles or is tough to open during service, especially when the hood is at full draw.
If one or two of these sound familiar, that's worth paying attention to. If most of them do, the kitchen is very likely short on makeup air.
What to Check Before You Call Anyone
A few things are worth ruling out yourself first, since they point to whether this is a simple fix or a bigger ventilation issue.
Check if the problem gets worse with exterior doors closed. If smoke clears better with a door propped open, that confirms the kitchen is pulling air from wherever it can get it, which points straight at a makeup air shortage rather than a hood or fan issue.
Think about whether anything changed recently. A new piece of cooking equipment, an added exhaust fan, a remodel, or a new wall that closed off an old air path can all shift how much makeup air a kitchen needs. If the hood worked fine until something else in the kitchen changed, that's usually the trigger.
Clean the hood filters and check the fan belt or motor anyway. It's worth ruling out the obvious. A dirty filter or a slipping belt can mimic some of the same symptoms, and it's a five-minute check.
If filters and the fan check out fine and the door test points to negative pressure, the hood isn't the problem. The building's air balance is.
Why This Matters Beyond a Smoky Kitchen
A kitchen that's short on makeup air doesn't just feel uncomfortable. It affects equipment that has nothing to do with the hood. Gas appliances that struggle to get enough combustion air run less efficiently and wear harder. HVAC systems work against the imbalance instead of with it, since they're constantly losing conditioned air to a kitchen that's pulling it in to compensate. None of that shows up as one big failure. It shows up as higher utility costs and equipment that needs service more often than it should.
For restaurant groups managing kitchens across more than one location, this is also a pattern worth tracking. If more than one location has the same complaint about smoke not clearing or doors being hard to open, it's worth checking whether those kitchens share a similar building age, layout, or hood installation history. A makeup air shortage at one site is a maintenance issue. The same complaint showing up at two or three sites is a design pattern worth reviewing across the portfolio.
When This Becomes a Call to Make
If the door test confirms negative pressure, or if the filters and fan are clean and the problem still isn't resolved, this moves past something you can diagnose from the kitchen floor. Correcting a makeup air shortage means looking at the building's full ventilation balance, not just the hood, which is a job for a technician who can measure airflow and size a fix correctly the first time.
Duotemp Mechanical works on commercial kitchen ventilation across Chicago, Naperville, and Oak Park, and sees this exact issue often in older buildouts and converted spaces. We'll walk through what's pulling air, what's replacing it, and what needs to change so your kitchen runs the way it's supposed to.
Frequently Asked Questions
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Makeup air is the air that replaces what your exhaust hood pulls out of the kitchen. Every hood needs a matching supply of incoming air, or the kitchen runs at negative pressure and the hood stops clearing smoke and grease the way it should.
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This usually means the hood and fan aren't the problem. The kitchen isn't getting enough makeup air to replace what the hood is exhausting, so the fan can't move air the way it's designed to.
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Check whether exterior doors are hard to open or slam shut during service, whether smoke lingers near the hood despite the fan running, and whether pilot lights flicker on gas equipment. These are the clearest signs of a negative pressure kitchen.
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It can mimic some of them, which is why it's worth cleaning filters and checking the fan belt or motor first. If those check out fine and the door test still points to negative pressure, the issue is the building's air balance, not the hood itself.
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Yes. It shows up often in older buildings and spaces converted into restaurants from a different use, where the original ventilation wasn't designed around a commercial kitchen exhaust load.
