Window & Door Heat Loss Calculator

Window ratings are given as U-factors (lower is better).

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Formula

Q = U × A × ΔT

Example calculation

60 ft² at U-0.30, 70 °F ΔT → 1,260 BTU/h.

Practical HVAC use

Compare window options.

Common mistakes

Using centre-of-glass U instead of whole-window U.

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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