Example: Wall/roof area: 2,800 sq ft · Average U-value: 0.09 · Design ΔT: 20 °F · Window area: 280 sq ft → Total heat gain: 19,000 BTU/hr.
In tons of cooling: 1.6
Solar/window share: 8,400 BTU/hr
Frequently asked questions
How do I calculate heat gain? Enter your numbers above and the result updates instantly. For example: Wall/roof area: 2,800 sq ft · Average U-value: 0.09 · Design ΔT: 20 °F · Window area: 280 sq ft → Total heat gain: 19,000 BTU/hr.
Is this Heat Gain Calculator free? Yes — completely free with no sign-up or paywall. It runs entirely in your browser and keeps working offline; the numbers you enter never leave your device.
How accurate is it? It uses the standard published formula for heat gain. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.