When a restaurant exhaust hood stops pulling properly, you know it within minutes. Smoke lingers over the grill, steam hangs in the air, grease smell fills the dining room, and the kitchen gets unbearably hot. It is not just uncomfortable — it is a fire risk and a health code issue. Here are the most common causes we see when we get called out for hood problems in Calgary restaurants.
1. The exhaust fan motor has failed or is dying
This is the most common cause of a hood that suddenly stops pulling air. The exhaust fan — usually mounted on the roof or at the end of the ductwork — is the engine of the whole system. When the motor fails, airflow stops completely. If the motor is on its way out, you may notice reduced suction, a grinding or squealing noise from the roof, or the fan cycling on and off inconsistently.
Fan motors in restaurant applications take a beating. They run for hours every day in a greasy, hot environment. Over time, bearings wear out, windings degrade, and the motor eventually gives up. If your hood went from working fine to barely pulling overnight, the fan motor is the first thing to check.
2. Grease buildup is choking the system
Even with a functioning fan, grease accumulation can slowly strangle your exhaust system. It starts with the baffle filters in the hood canopy. When those are not cleaned regularly — ideally every week or two depending on your cooking volume — grease starts building up in the ductwork itself. Over months and years, that buildup narrows the duct passage and restricts airflow significantly.
If your hood used to work great and has been gradually getting worse, grease restriction is a likely culprit. Get your filters on a proper cleaning rotation and have the ductwork professionally cleaned at least once or twice a year. Beyond airflow, this is also a fire prevention issue — grease-laden ductwork is a serious fire hazard.
3. A belt-driven fan has a broken or slipping belt
Many commercial exhaust fans use a belt-drive system where a motor turns a belt that spins the fan wheel. If that belt snaps, you lose all exhaust instantly. If the belt is worn, loose, or glazed, it may slip — meaning the motor runs but the fan wheel does not spin at full speed. The result is weak, inconsistent airflow.
Belt issues are one of the easier fixes in exhaust hood service. The belt itself is inexpensive, but it needs to be the right size and properly tensioned. If your fan motor sounds like it is running but the hood is not pulling, a broken belt is high on the list of suspects.
4. Make-up air is not balanced
This is the one that confuses a lot of restaurant owners. An exhaust hood does not just pull air out — it needs replacement air coming in to work properly. That replacement air is called make-up air. If your building is too tight, the make-up air system is not working, or someone sealed off a vent, the exhaust hood has to fight against negative pressure to pull air out.
Signs of an airflow imbalance include doors that are hard to open or slam shut on their own, a whistling sound from gaps around doors or windows, and a hood that seems to work better when you prop the back door open. If opening a door dramatically improves your hood performance, the problem is almost certainly make-up air related.
5. Electrical or control issues
Sometimes the exhaust system hardware is fine, but it is not getting the signal to run. A failed switch on the hood control panel, a wiring issue between the switch and the fan, or a breaker that keeps tripping can all shut down your exhaust. If the fan runs sometimes but not others, or if it stopped working after a power outage, the issue may be electrical rather than mechanical.
These problems need a technician to diagnose safely. Exhaust fans run on higher voltage circuits, and rooftop units involve working at height. This is not a good area for DIY troubleshooting.
6. What to do right now
If your exhaust hood is not working, the safest thing to do is reduce or stop cooking — especially anything that produces heavy smoke or grease. Open exterior doors to create some cross-ventilation and keep the kitchen livable. Do not attempt to run cooking equipment at full capacity without exhaust — the grease and smoke buildup is a real fire risk, and your local fire inspector will not be understanding about it.
YYC Mechanical handles exhaust hood and kitchen ventilation repair across Calgary. Whether it is a dead fan motor, a belt replacement, or a make-up air issue, we can get your kitchen ventilation back in order. If your hood is down, call us and we will get it sorted out.