Furnace Size Calculator :
Find Your BTU Capacity in Seconds

Furnace size calculator helps you estimate the right BTU capacity for your Ontario home,
based on square footage and climate zone, for better comfort, lower bills, and a longer-lasting system.
📐 Accurate Sizing
🇨🇦 Climate Zones Included
⚡ Instant Result
📐
Furnace Size & BTU Calculator
Not sure what size furnace you need? Answer a few questions about your home and we’ll calculate the right BTU output for your situation.
Select your home type
Approximate home square footage of finished living space
What year was your home built?
How well-insulated is your home?
Does your home have lots of large windows, patio doors, skylights, or a sunroom?
Which part of Canada/North America do you live in?
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📐 BTU Calculation Complete
Your Recommended Furnace Size
Recommended Furnace Output
—
BTUs per hour

What This Means

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What Size Furnace Do I Need in Canada?

Choosing the correct furnace size is one of the most critical decisions when replacing your heating system.. An oversized furnace short-cycles it turns on and off too frequently, wasting energy and creating uneven temperatures. An undersized furnace runs constantly and struggles to heat your home on the coldest days. The right size depends on a proper heat load calculation.
Home Size
(sq ft)		Recommended BTU
(Moderate Climate)		Recommended BTU
(Cold Climate)
800 – 1,00040,000 – 50,000 BTU50,000 – 60,000 BTU
1,000 – 1,50050,000 – 65,000 BTU65,000 – 80,000 BTU
1,500 – 2,00065,000 – 80,000 BTU80,000 – 100,000 BTU
2,000 – 2,50080,000 – 100,000 BTU100,000 – 120,000 BTU
2,500 – 3,500100,000 – 120,000 BTU120,000 – 140,000 BTU
These are general estimates. A professional CSA F280 heat loss calculation accounts for insulation, windows, climate zone, and air sealing.

Factors That Affect Furnace BTU Requirements

📏 Square Footage
The primary driver of BTU requirements. Measure all heated living space including basements if heated.
🌡️ Climate Zone
A home in Winnipeg (-33°C design temp) needs significantly more BTU capacity than the same home in Victoria (-3°C design temp).
🏗️ Insulation Quality
Homes with Homes with proper attic, wall, and basement insulation require 20–30% less heating capacity than poorly insulated homes.
🪟 Windows & Doors
Large or poorly sealed windows increase heat loss significantly. Triple-pane windows reduce BTU requirements compared to single-pane.
📐 Ceiling Height
9-foot or higher ceilings increase total heated volume. Use actual ceiling height, not just square footage, for accurate sizing.
🔄 Duct System Condition
Leaky or uninsulated ducts can reduce effective heat delivery by 20–30%, meaning you may need a higher BTU furnace to compensate.

Furnace Sizing by Canadian Climate Zone

Canada's climate zones span from Zone 4 (mild coastal BC) to Zone 8 (arctic communities). The National Energy Code for Buildings uses heating design temperatures to establish BTU requirements. Use our calculator above to get your zone-specific recommendation.
Province/RegionDesign TempBTU Multiplier
Vancouver, BC3°CLow (×30–35)
Toronto, ON-20°CMedium (×40–45)
Calgary, AB-29°CHigh (×45–50)
Winnipeg, MB-33°CVery High (×50–60)
Edmonton, AB-31°CHigh (×48–55)

FAQ For Furnace Size Calculator

What happens if my furnace is too big for my home?

An oversized furnace short-cycles, wasting energy and causing uneven temperatures and humidity problems.

Furnaces are sized in BTU/h (40,000–140,000 typical); tonnage applies to air conditioners, not furnaces.

Online calculators give a solid starting estimate, but a licensed HVAC contractor's load calculation is required for final sizing.

Rebates Available
Federal rebate programs change often. The original Canada Greener Homes Grant is closed to new applicants.
$5,000
Check Natural Resources Canada's current incentive list for what's active in your province before budgeting for a rebate.
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