Heat Loss Calculator

Estimate heat loss through a building element.

HEAT LOSS
— BTU/hr
through this surface

Usage Tip

Add up all surfaces (walls, ceiling, floor, windows) to get your total home heat loss.

THE MATH
Q = Area × ΔT ÷ R
Where: ΔT = indoor − outdoor temp  •  R = assembly R-value
• Per sq ft = ΔT ÷ R
• Annual cost assumes continuous gas heat at $1.20/therm
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.