Home / Services / Commercial HVAC / Commercial Exhaust Fan Repair
Commercial · Commercial Exhaust Fan RepairCommercial Exhaust Fan Repair & Replacement
Commercial exhaust fan repair and replacement starts with the drive: a belt-drive fan that has stopped moving air nearly always needs a belt, bearings or a sheave, and a direct-drive fan that has stopped needs a motor or a speed control. Repair makes sense while the wheel and housing are sound; replace the fan when the housing has corroded through, the wheel is damaged, or the bearings and motor have both gone. A replacement is matched to three things: the existing roof curb, the airflow in litres per second and the static pressure of the duct.
Belt-drive rooftop fans, both upblast and downblast, fail in a predictable order. The belt stretches, glazes and finally snaps, and a fan with a broken belt sounds normal from the ground because the motor still runs. Bearings on the fan shaft dry out and start to growl, a worn sheave eats new belts in weeks, and a motor that has been dragging a seized bearing burns out last. Replacing the belt without checking the sheaves and bearings is why the same fan fails again a month later.
Direct-drive fans have no belt, so the list is shorter: the motor, its capacitor, and the speed control that sets airflow. Newer fans use electronically commutated motors with a built-in speed dial, and the motor and its electronics are replaced as one piece. Inline and ceiling fans serving washrooms, janitor rooms and storage are the smallest and the most ignored. When they die the complaint is odour or damp, not a broken fan, and many turn out to have been dead for a long time.
Kitchen fans are their own category. A fan serving a grease hood must be an upblast type that throws exhaust up and away from the roof, and NFPA 96, the standard the Ontario Fire Code relies on for commercial cooking exhaust, calls for a hinge kit so the fan can be tipped back for cleaning and a grease container so drippings do not soak the roof. A downblast fan on a grease duct is a deficiency however well it runs. Our scope is the fan itself — motor, bearings, belts, wheel, hinge, wiring and controls — while degreasing the hood, duct and fan is a separate certified trade.
An exhaust fan is half of a pair. Whatever it removes has to be replaced by a make-up air unit or by outdoor air through the rooftop units, and the two are normally interlocked so one cannot run without the other. A dead exhaust fan leaves the kitchen full of smoke; a dead make-up air unit leaves the exhaust fan pulling against a vacuum, with doors that are hard to open and gas appliances that spill. When either side fails we check both, and the measuring side of that work is on our kitchen exhaust and make-up air balancing page.
Replacement fans are selected from the old fan's nameplate and the duct it serves, not from the catalogue page that looks similar. We match the curb dimensions so the roof is not reopened, then pick a fan whose curve delivers the required litres per second at the system's static pressure; a fan chosen on airflow alone will underperform on a long or dirty duct. Restaurant-wide ventilation is covered on the restaurant HVAC page and other equipment under commercial HVAC. If a kitchen fan has quit during service, stop cooking under that hood and call the shop.
Equipment we install and service
The mushroom-shaped fan over most kitchen hoods and many general exhaust ducts. Belts, shaft bearings, adjustable sheaves and the motor are all serviceable, and the wheel needs to be clean and balanced to stop vibration from destroying new bearings.
Low-profile domed fans that discharge down toward the roof, used for washrooms, storage and general ventilation where there is no grease. Same belt and bearing wear, plus backdraft dampers that stick open and let winter air fall into the building.
The motor is mounted on the wheel, with a speed control or dial in place of pulleys. Fewer parts and less maintenance; when the motor fails the fan stops completely, with no warning squeal.
Fans mounted in the duct or ceiling serving washrooms and small rooms. Usually replaced outright, sized to the duct and room, and checked for a working damper and a clear discharge.
What goes wrong in these buildings
- The hood is on but smoke is rolling out the front and filling the kitchen.
- There is a screech from the roof every time the fan starts.
- The back door slams itself shut and the front door whistles.
- The washrooms smell and the fan switch does nothing.
- We put a new belt on last month and it has already shredded.
- The hood cleaners say our fan has no hinge and they cannot clean it properly.
How it works
On the roof with the power locked out: belt, sheaves, bearings, wheel, motor amps and damper. Indoors we check the switch, starter or speed control and whether the make-up air is running.
Belts, bearings and sheaves are replaced as a set where they have worn as a set, and alignment and tension are set properly. The written price comes before the parts go in.
If the fan is finished, the new one is selected for the existing curb, the required litres per second and the measured static pressure, with a hinge kit and grease containment on kitchen duty. Airflow is confirmed after start-up.
Common questions
Our kitchen exhaust fan died during service — can we keep cooking?
No. Without exhaust, heat, smoke and combustion gases from the line stay in the kitchen, and many hoods are interlocked to shut off gas to the appliances when the fan stops. Turn off the cooking equipment and call our emergency line, which is answered at all hours. A snapped belt is frequently a one-visit repair, so the outage can be short.
Do you clean the grease out of the fan and duct?
No. Hood, duct and fan degreasing is done by certified kitchen exhaust cleaners who issue the service sticker your insurer and fire inspector look for. We handle the mechanical side: motor, bearings, belts, wheel, hinge kit, wiring and the interlock. Booking both trades for one visit works well, since the fan is already tipped open.
Should we repair or replace an old rooftop exhaust fan?
Repair it if the housing and wheel are solid; belts, bearings and motors are routine. Replace it when the housing is rusted through, the wheel is bent or cracked, parts are no longer made, or the fan was the wrong type for the duty, such as a downblast fan on a grease duct. A fan needing a motor, shaft and bearings at once is usually at that point.
Why does a new fan need airflow and static pressure numbers?
Because a fan does not deliver a fixed airflow; it delivers whatever its curve allows against the resistance of the duct, hood and filters. Two fans with the same nominal size can move very different volumes on the same duct. We read the old nameplate, measure static pressure where we can, and select the replacement to hit the required litres per second.
Related
Keep the building running.
One licensed team for installs, maintenance contracts and 2 AM calls.