Heating a Garage or Workshop in Winter Without Wasting Money
General information only. Gas appliances and new electrical circuits or outlets belong to licensed trades. Follow the heater manufacturer's instructions for clearances and use, and your local codes, wherever they differ from the general guidance here.
The cheapest garage to heat is the one that is only warmed while someone is working in it. That single decision — heat on demand, versus holding the space warm all winter — matters more than the heater brand, the fuel, or the thermostat. Everything below follows from it: seal the shell first, size for the job actually chosen, and run the heater for hours per week instead of hours per day.
Job summary
Difficulty: sealing and insulating are ordinary DIY; a hardwired heater or a new circuit is not — that part is a licensed electrician's job, and gas units are a licensed gas fitter's job. Time: a weekend covers the door seals, the house-wall sealing, and a portable or plug-in setup; insulation and a hardwired install are a longer project. Cost: no product prices are quoted here, because none were verified for it — the running-cost section shows the arithmetic to run with your own rate and your own quotes. Hire a pro instead for any gas appliance, any new outlet or circuit, and any heater whose manual calls for hardwired installation.
First decide: freeze protection or a warm workshop
Freeze protection means holding the garage just above freezing so pipes, paint, and stored liquids survive. The heater runs at a low setting, cycles modestly, and comfort is not the goal.
A warm workshop means working in shirtsleeves for a few hours at a time. The heater runs hard during those sessions and sits idle — or at the freeze-protection setting — the rest of the week.
The expensive pattern is the third one, chosen by default rather than on purpose: holding workshop temperature around the clock for a space used a few evenings a week. The cost section below prices that difference directly.
Seal and insulate before sizing anything
A utility warning frames the whole job: even the best garage heater cannot overcome poor insulation, and many garages — detached ones especially — lack proper insulation, causing significant heat loss and higher operating costs (s1). Sizing a heater for an uninsulated garage locks in the oversized heater and the oversized bill together.
For an attached garage, Natural Resources Canada's retrofit guide is specific about the shared boundary: the walls, ceiling, and door adjoining the house must be insulated and air sealed, which reduces heat loss and prevents garage fumes from entering the house (s2). Any holes cut in that ceiling get carefully resealed, for the same fume reason (s2). One option is off the table entirely: never run heating supply and return ducts from the house into a garage — NRCan states this is dangerous and violates all codes (s2). A garage gets its own heat source, or it stays cold.
Heater options compared
| Option | Sizing guide | Running-cost character | Installation line |
|---|---|---|---|
| Natural gas unit heater | 30,000–40,000 BTU for a typical two-car garage; upwards of 45,000 BTU for three cars (s1) | Delivers fast, powerful heat in cold snaps; natural gas tends to cost less per unit of energy than electricity, so gas is more economical for large loads (s1) | Licensed gas work; fuel-burning appliance rules and annual professional inspection apply (s1) (s3) |
| Electric heater, 240V | Roughly 10 watts per square foot of space (s1) | Nearly 100 percent conversion efficiency and easier installation, especially detached with no gas hookup — but electricity often costs more per kilowatt-hour than the equivalent energy in gas (s1) | Plug-in models still need their specified 240V receptacle; hardwired models and new circuits are electrician work (s5) (s6) |
| Portable electric heater | Bench-scale warmth for one work area, not whole-garage sizing | Same per-kilowatt-hour cost as any electric heat; waste is limited only if sessions are short | At least 1 metre from combustibles, never on an extension cord or power bar, unplugged before leaving or sleeping (s4) |
| Propane or other fuel-fired portable | Not sized here | Fuel cost is only part of the picture | Never use propane, kerosene, or oil space heaters in enclosed areas unless specifically designed for indoor use (s3) |
Whichever row wins, many heating products sold in Canada must meet efficiency requirements under the federal Energy Efficiency Act, and Natural Resources Canada's searchable product list covers gas-fired unit heaters and electric heaters — a certification and listing check worth doing before money changes hands (s1).
What it costs to run: redo the math at your rate
Electric heat makes the arithmetic honest, because the formula is one line: kilowatts × hours × your rate per kilowatt-hour. A 5 kW heater is the worked size here because the sizing guideline of roughly 10 watts per square foot (s1) puts a 500-square-foot garage at about 5,000 watts. The rate used below — $0.15 per kilowatt-hour — is a labelled assumption for illustration, not a quote for any province. Substitute your own bill's rate.
| Pattern (labelled assumptions) | Energy | Cost at $0.15/kWh |
|---|---|---|
| Workshop sessions: 5 kW × 3 hours × 10 sessions a month | 150 kWh | $22.50 a month |
| Longer sessions: 5 kW × 4 hours a day × 20 days | 400 kWh | $60 a month |
| Held warm continuously: 5 kW × 24 hours × 30 days, heater running flat out | 3,600 kWh | $540 a month |
The last row is a ceiling, not a prediction: a thermostat cycles the heater off once the setpoint is reached, so a real always-warm garage lands somewhere between the session rows and that ceiling, with insulation quality deciding where. The point stands at any rate and any cycling pattern — hours of runtime are the multiplier a household controls, and the session pattern cuts them by an order of magnitude. Gas heat follows the same shape at a lower per-unit energy cost for large loads (s1); the decision order does not change.
The setup, in order
- Name the job in one sentence — freeze protection, warm workshop sessions, or both — and write down the hours per week the space is actually used. Success check: the sentence, not a vague "warm garage," drives every later choice.
- Seal the overhead door and the house boundary. Weatherstrip the overhead door's edges, then insulate and air seal the walls, ceiling, and door adjoining the house (s2). Success check: no daylight and no felt draft at the door edges on a windy day, and the house-side door closes against a sealed frame.
- Insulate before buying heat. Walls and ceiling first; an uninsulated shell defeats any heater and inflates its running cost (s1). Success check: the shell work is finished, not planned, before a heater size is chosen.
- Size from the guideline, then verify. Electric at roughly 10 watts per square foot; gas at 30,000–40,000 BTU for a two-car garage (s1). Success check: the chosen unit's rating sits at the guideline for the measured floor area — not a size up "for safety."
- Place the heater by its own manual's clearances. One manufacturer's manual requires 26.5 inches (67 cm) from floor to heater bottom when the mounted unit is tilted, and 3.5 inches (9 cm) from ceiling to heater top when ceiling-mounted (s5); a hardwired unit's manual requires mounting at least 8 feet (2.44 m) above the floor (s6). These figures differ by model — the manual for the unit in hand governs. Success check: every clearance in that manual is measured, not eyeballed.
- Put new circuits and hardwiring with a licensed electrician. The Cadet manual instructs using a licensed electrician to install new outlets or circuits (s5), and hardwired models require a certified electrician working to applicable national and local codes (s6). Success check: the install is inspected and the breaker is labelled for the heater circuit.
- Set the thermostat to the job. Freeze-protection setting when the space is empty; session temperature only while working. Success check: a week later, the heater's runtime matches the hours written down in step 1, not the whole week.
What success looks like: the garage reaches a workable temperature within a session, holds just above freezing between sessions, the house-side rooms smell of nothing from the garage, and the first month's bill matches the session row of the cost table rather than surprising anyone.
Safety lines that are not optional
Carbon monoxide. CO cannot be seen, smelled, or tasted; only a carbon monoxide alarm detects it (s3). Never idle a vehicle in the garage, even with the overhead door open, and keep the door between house and garage closed (s3). Fuel-burning appliances get a professional inspection at least once a year, and exhaust vents get checked during and after snowstorms for ice and snow blockages (s3). If an alarm sounds: leave for fresh air at once, do not hunt for the source, call 9-1-1 from outside, and return only after a professional has fixed the problem (s3).
Clearances and combustibles. Portable electric heaters stay at least 1 metre from combustible materials (s4). A hardwired heater with hot and arcing parts inside must not be used where gasoline, paint, or flammable liquids are used or stored (s6) — a real constraint in a working garage, and a reason some shops belong with a different heater type placed by its manual, or with no fuel-fired unit at all.
Electrical. Never plug a portable electric heater into an extension cord or power bar, and unplug it before leaving home or going to sleep (s4). Look for a recognized Canadian certification mark such as CSA, cUL, or cETL on electrical products (s4).
Common mistakes
Buying the heater first. An oversized unit bought for an uninsulated shell costs more to buy, more to run, and still leaves the bench cold by the door. The seal-and-insulate order in the procedure exists because the utility guidance is blunt about which one wins (s1).
Heating the neighbourhood schedule. A timer or thermostat holding workshop temperature through every night and workday multiplies runtime for nobody's benefit. The fix is the step-7 setting, not a bigger heater.
Borrowing the house's heat. Cutting a house duct into the garage feels free and is the one move the official guidance forbids outright — dangerous, and a code violation (s2). The garage's heat source stands alone, sized for the garage's own job.
— Tom Reilly, Home & DIY Writer