By Commercial Service Company · August 24, 2026
A kitchen hood is easy to ignore until it stops keeping up. The cook line gets hot, smoke drifts out toward the dining room, the back door is hard to pull open, and everybody assumes the hood is "getting old." Nine times out of ten the hood is fine. What changed is the air moving through it — or the equipment that moves it.
Here is what we look at on a commercial kitchen exhaust repair call, in the order it usually matters. This is not a hood-cleaning article; cleaning is a separate, scheduled job handled by a certified hood cleaning company. This is about why the system stopped pulling.
Exhaust and Make-Up Air Have to Balance
Every cubic foot of air your exhaust fan pulls out of the building has to come back in from somewhere. That is what a make-up air (MUA) unit is for — it delivers tempered replacement air near the cook line so the hood has something to work with.
When make-up air falls behind exhaust, the kitchen goes into negative pressure, and you see it long before you measure it:
- Exterior doors that fight you on the way out, or whistle at the seams
- Smoke rolling out from under the hood lip instead of being captured
- Pilot lights and burner flames that wander or blow out
- Cold drafts in the dining room as air gets sucked in through the front of the house
- Dust streaks at door frames and ceiling tiles that lift at the corners
Negative pressure also drags conditioned air out of the dining room, so your rooftop units run longer and the front of the house never quite settles. In an Arkansas August, that shows up on the power bill and in customer complaints on the same week.
Balance goes bad for ordinary reasons: a MUA unit that shut down and nobody noticed, a filter bank so loaded it strangles supply air, a new piece of cooking equipment added under an existing hood, a damper stuck closed, or a remodel that sealed up the makeshift openings the building had been breathing through.
Belts, Bearings, and Motors
Most rooftop exhaust fans and many make-up air units are belt-driven. Belts stretch and glaze. A loose or worn belt slips, the fan wheel turns slower than it should, and airflow drops off gradually enough that the staff adapts instead of calling. The fan still sounds like it is running.
Things that quietly cut your airflow:
- Stretched, cracked, or glazed belts and misaligned sheaves
- Dry or failing bearings — usually announced by a rumble or squeal
- Grease-loaded fan wheels, which throw the fan out of balance and beat up the bearings
- Motors running hot, tripping on overload, or cycling on and off
- Loose mounting hardware and worn vibration isolators
Belt tension, alignment, bearing condition, and wheel cleanliness are what a scheduled PM visit is for. Catching a glazed belt is cheap. Replacing a motor and a bearing set after the wheel has been wobbling for a year is not.
Motor and electrical work — amp draws, overloads, contactors, starters, VFDs, wiring — belongs to a licensed technician. Rooftop fan work also means roof access and live equipment. Do not send a cook up there.
Controls Are Where the Surprises Live
Modern hood systems are wired together on purpose. Exhaust and make-up air are interlocked so one does not run without the other. Temperature sensors or a duct thermostat can start the fan automatically. Variable-speed controls ramp the fan up during a lunch rush and back down when the line is idle. The fire suppression system is tied in as well, and it will shut down gas and fuel when it trips.
Common control-side failures we find:
- Interlock broken after a repair, so exhaust runs with no make-up air
- A switch or breaker left off, so the MUA unit never starts
- A failed sensor holding fan speed low all shift
- A variable-speed drive faulted or stuck at minimum
- A hood turned off at the panel because "it was too loud"
These are also code-and-inspection items. Fire suppression, interlocks, duct condition, and clearances get looked at by the fire marshal and the health inspector. Anything touching the suppression system or the gas train is licensed work — we coordinate it, we do not improvise it.
What You Can Check, and What to Hand Off
Owner-level checks are simple and worth doing: confirm the make-up air unit is switched on and the breaker is set, look for filters that are obviously blinded over, note whether the doors have gotten hard to open, and listen for a new rumble or squeal on the roof. Write down when the problem happens — only during dinner rush, only on the fryer side, only when the dish machine runs — because that pattern tells a technician a lot.
Everything past that — measuring airflow, adjusting belts and sheaves, electrical diagnosis, dampers, sensors, gas-fired make-up air heat sections — is technician work. Guessing on a hood system risks a fire code violation, a failed inspection, or somebody hurt on a roof.
Call Commercial Service Company
We have been keeping central Arkansas kitchens running since 1976 — restaurants, grocery, schools, and institutional kitchens in Conway, Little Rock, Benton, Bryant, Maumelle, Jacksonville, Searcy, Russellville and the surrounding area. If your line is hot, your hood is not pulling, or your doors are fighting you, call us at 501-548-2374 and we will get a technician out to find out why.