BTU Heater Size Calculator
Estimate how many BTUs of heating a room or home needs, using Canadian climate zones. Useful for sizing a space heater, garage heater, furnace, or heat pump before you talk to a contractor.
Your results
Worked example
A 1,000 sq ft home in a cold climate zone, with 8 ft ceilings and average insulation:
- Base load: 1,000 sq ft × 45 BTU per sq ft = 45,000 BTU/hr
- Ceiling adjustment: 8 ft ÷ 8 ft = 1.0, so no change
- Insulation adjustment: average = 1.0, so no change
- In kilowatts: 45,000 ÷ 3,412 = 13.2 kW
If the same home had 10 ft ceilings, the estimate would rise to 45,000 × (10 ÷ 8) = 56,250 BTU/hr. If it also had poor insulation, it would rise again to 56,250 × 1.25 = 70,313 BTU/hr, which shows why tall, drafty spaces cost so much more to heat.
How this calculator works
This is a rule-of-thumb estimate, the same starting point many installers use before doing a full heat-loss calculation:
The climate factors are stated openly: 25 BTU per sq ft for mild coastal areas, 35 for moderate, 45 for cold, and 55 for very cold and arctic regions. The ceiling factor scales the result because heating load follows the volume of air and the wall area, not just the floor. Insulation adjusts the estimate by plus 25 percent (poor), zero (average), or minus 15 percent (good). Kilowatts use the standard conversion 1 kW = 3,412 BTU/hr. A proper equipment decision still needs a CSA F280 heat-loss calculation, which accounts for windows, orientation, and air leakage in detail. Use this result to compare quotes and spot ones that are wildly over or under sized.
Once a size looks right, compare what each system costs to run with the Heating Cost Comparison Calculator, and check how cold a period really was with the Heating Degree Days Calculator.
Common questions
Is a bigger heater always better?
No. An oversized furnace or heater cycles on and off, wears faster, heats unevenly, and can cost more to run. A unit close to your calculated load, sized up only modestly, is usually the better buy. Heat pumps are a partial exception, since cold-climate models are often sized with some extra capacity for the coldest days.
What zone is my city in?
As a rough guide: coastal British Columbia is mild; the Greater Toronto Area, southern Ontario, and the Atlantic provinces are moderate; the Prairies, northern Ontario, most of Quebec, and the interior of BC are cold; the territories and far northern communities are very cold. Borderline cases are common, so when in doubt, pick the colder zone for a space heater and the moderate one for a whole-home system a contractor will verify.
How do BTUs relate to watts and kilowatts?
Electric heaters in Canada are often sold by watts. Divide BTUs by 3,412 to get kilowatts, or multiply kilowatts by 3,412 to get BTUs. A standard 1,500 W plug-in heater, for example, puts out about 5,118 BTU/hr, enough for a small room.
Does this work for a single room or a garage?
Yes. Enter just that space's floor area. Garages and workshops usually rate as poor insulation unless they are properly insulated and sealed, and they often have higher ceilings, so enter the real ceiling height.
Estimates only, based on rule-of-thumb factors stated on this page. This calculator is a planning aid, not an engineering heat-loss calculation. Heating equipment should be sized and installed by a licensed contractor using a recognized method such as CSA F280. Mississippi Maple accepts no liability for equipment decisions made using this calculator.