Example: Surface area (walls+roof+windows): 3,200 sq ft · Average U-value: 0.09 BTU/hr·ft²·°F · Indoor design temp: 70 °F · Outdoor design temp: 10 °F → Heat loss: 17,500 BTU/hr.
With 15% infiltration allowance: 20,000 BTU/hr
Frequently asked questions
How do I calculate heat loss? Enter your numbers above and the result updates instantly. For example: Surface area (walls+roof+windows): 3,200 sq ft · Average U-value: 0.09 BTU/hr·ft²·°F · Indoor design temp: 70 °F · Outdoor design temp: 10 °F → Heat loss: 17,500 BTU/hr.
Is this Heat Loss 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 loss. Results are estimates for planning — not financial, tax, medical, engineering, or legal advice.