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Commercial · Commercial Unit Heater Repair & InstallationCommercial Unit Heater Repair & Installation
Commercial unit heater repair and installation splits on one part. A hot-surface igniter, a flame sensor, a pressure switch or a fan motor is swapped on site with the heater still hanging; a heat exchanger that is cracked or rusted through cannot be patched, so the heater is tagged out of service and replaced. ZK Mechanical repairs and installs gas-fired unit heaters of the Reznor and Modine type in warehouses, shops and garages from Burlington to Brampton.
A gas unit heater lights in a fixed sequence, and where it stops tells us the part. The venter motor starts and a pressure switch proves draft, the hot-surface igniter glows, the gas valve opens, the flame sensor confirms flame, and the fan starts once the heat exchanger is warm. A pressure switch that will not close stops everything before ignition, while a flame that lights and drops out a few seconds later is a dirty or failed flame sensor. A burner that runs with no fan behind it means a seized fan motor, and the heater will cycle on its high limit until the motor is replaced.
The heat exchanger decides whether the heater has a future. Tubes rust from the inside when a heater short-cycles or hangs in a humid building, and a crack or perforation lets combustion products into the airstream that the fan blows across the shop. That is an unsafe condition under Ontario's gas rules: the technician shuts the appliance off and tags it, and it stays off until it is corrected. Igniters, sensors, switches, motors, venters and gas valves are repairs; a failed heat exchanger on an older heater is a replacement.
Unit heaters come in three venting types, and the building picks the type. Gravity-vented heaters use a draft hood and room air, which suits clean, dry, neutral-pressure spaces; power-vented heaters use a fan to push flue gas through a sealed Category III vent, which allows a sidewall termination. Separated-combustion heaters pipe their combustion air in from outdoors and keep the burner sealed from the room. Dusty woodshops, humid wash bays and buildings pulled negative by large exhaust fans all need separated combustion, because dust fouls burners, moisture and chemical vapours corrode heat exchangers, and negative pressure pulls flue gas back down a gravity vent.
Installation is governed by CSA B149.1 and the heater's rating plate. Clearances to combustibles above, below and beside the heater come from the certified installation instructions, racking and stored goods count as combustibles, and repair garages have a minimum mounting height above the floor that keeps the burner out of the layer where fuel vapour collects. Gas piping is sized for the heater's input and the length of the run, which in a long warehouse often means a larger line than the old heater had. Shops on propane in rural Caledon and Flamborough need the heater ordered or converted for that fuel.
Sizing is a heat-loss calculation in BTU/h, adjusted for the two things that defeat unit heaters: ceiling height and door openings. Warm air collects under a high roof deck, so tall buildings need heaters with enough throw to reach the floor, or ceiling fans to push the heat back down, and every dock door that cycles needs capacity near it. Our warehouse and industrial HVAC page covers the whole building, and infrared tube heaters are the alternative where doors stay open. Start at commercial HVAC for other equipment, or ask for a site visit.
Equipment we install and service
The older standard: a draft hood, a vertical vent through the roof and combustion air taken from the room. Simple and durable in clean, dry buildings, and the first to backdraft when exhaust fans are added or the building is tightened.
A venter motor pushes flue gas through sealed Category III vent pipe to a roof or sidewall cap. Venter motors and pressure switches are the added wear parts, and vent joints must stay sealed because the vent runs under positive pressure.
Combustion air and flue gas are both piped to outdoors, with the burner compartment closed to the room. The right choice for dust, humidity, solvents or negative pressure, usually paired with a stainless steel heat exchanger where corrosion is the concern.
Thermostats mounted at working height away from doors, fan-delay controls, and ceiling fans that push stratified heat down. A thermostat hung beside a dock door will run the heater all day.
What goes wrong in these buildings
- The heater clicks and glows, lights for a few seconds and shuts off again.
- The burner is running but no air is coming out the front.
- It is warm at the roof and cold at the floor where people are working.
- The heater by the dock door cannot keep up when trucks are loading.
- Rust flakes are falling out of the bottom of the heater.
- We added a paint exhaust fan and now the old heaters smell of fumes.
How it works
We watch the heater try to light, find the step that fails and test the part. Heat exchanger, venting and gas pressure are checked on every call, whatever the complaint.
Repairable faults are priced in writing and fixed, usually in that visit. If the heat exchanger has failed, the heater is shut off and tagged, and you get a replacement quote sized for the space as it is used now.
New heaters are hung at the certified clearances, vented in the listed vent type, piped and leak-tested, then set up with a combustion and gas-pressure check. Lift access and work around racking are planned with your shift schedule.
Common questions
Is it worth repairing an old unit heater?
Yes, if the heat exchanger is sound. Igniters, flame sensors, pressure switches, venter motors and fan motors are ordinary parts, and unit heaters are simple, long-lived machines. The rule flips once the heat exchanger is cracked or perforated: the part costs a large share of a new heater, and on an older unit it is not worth installing.
What is a red tag on a unit heater?
It is a warning tag a licensed gas technician must attach when an appliance is unsafe. For an immediate hazard, such as a perforated heat exchanger or flue gas spilling into the building, the gas to that heater is shut off on the spot. The tag stays until the fault is corrected by a licensed contractor, which for a failed heat exchanger means replacement.
How many unit heaters does a warehouse need?
It depends on the building's heat loss, the ceiling height and the number and use of the doors, so we calculate it and do not guess from floor area. Several smaller heaters spaced along the walls usually heat more evenly than one large unit, and a heater aimed across each frequently opened dock door handles the load that causes most complaints.
Can a unit heater go in an auto repair garage?
Yes, with conditions. The gas code sets a minimum mounting height in repair garages so the burner sits above the level where fuel vapours gather, and clearances to vehicles on hoists apply. Where paint, solvents or heavy exhaust extraction are involved, a separated-combustion heater is the safe choice. We confirm the requirements against the heater's certified instructions before quoting.
Related
Keep the building running.
One licensed team for installs, maintenance contracts and 2 AM calls.