Building Heat Loss Estimate
Sums conduction through each surface and infiltration heat loss at design temperature.
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Simplified — excludes below-grade losses, ventilation, internal and solar gains.
Formula
- Q = Σ(A ÷ R) × ΔT + Σ(U × A) × ΔT + 0.018 × V × ACH × ΔT
Example calculation
A modest 1,500 ft² house often lands in the 25,000–45,000 BTU/h range depending on envelope and climate.
Practical HVAC use
Ballpark equipment size before a proper CSA F280 or Manual J calculation.
Common mistakes
- Sizing equipment from this estimate alone.
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Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators