Calculator
Imperial (°F / ft²)
Metric (°C / m²)
Canadian City Design Temperatures (Optional)
— Select a city to auto-fill —
Edmonton, AB
Calgary, AB
Winnipeg, MB
Toronto, ON
Ottawa, ON
Vancouver, BC
Halifax, NS
Outdoor Design Temperature — Heating (°F)
Indoor Setpoint (°F)
Conditioned Floor Area (ft²)
Ceiling Height (ft)
Wall Insulation Level
Poor — older home, minimal insulation (R-7 or less)
Below average — some insulation, older construction (R-11)
Average — standard residential (R-19 to R-22)
Good — well insulated modern home (R-24 to R-30)
Excellent — high performance build (R-40+)
Window Area (% of floor area)
Low — 8% or less (few small windows)
Typical — 12% (standard residential)
High — 18% (many or large windows)
Very high — 25%+ (open concept, lots of glazing)
Construction Tightness / Infiltration
Leaky — older home, no air sealing (ACH ~0.8)
Average — typical residential (ACH ~0.5)
Tight — modern construction, some air sealing (ACH ~0.25)
Very tight — HRV, full air sealing (ACH ~0.10)
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Estimated Heating Load
0 BTU/hr
Enter values above and click calculate.
How It Works
This calculator estimates the heating load for a residential space using
floor area, ceiling height, insulation levels, window area, and local
design temperatures. It is a simplified Manual J approach suitable for
quick estimates during the quoting and planning stages.
Heating Load = Envelope Loss + Infiltration Loss
Where:
Envelope Loss = (Wall U-value + Window U-value) × Floor Area × ΔT
Infiltration Loss = (Volume × ACH ÷ 60) × 1.08 × ΔT
ΔT = difference between indoor setpoint and outdoor design temperature
0.018 = specific heat of air in BTU/ft³·°F
Canadian design temperatures used in this calculator:
Common example: A 1,500 ft² average home in Edmonton at −28°C outdoor design
temp with standard insulation and typical windows requires approximately
55,000–65,000 BTU/hr of heating output.