Boiler Size Calculator
Find the right boiler output (BTU/hr) for your home. Enter your heated area, climate zone, and insulation quality for an instant size estimate with 10% headroom.
Better insulation lowers the heating load.
99,000 BTU/hr
Recommended boiler output (incl. 10% headroom)
Estimates only. Final sizing and pricing confirmed by a certified installer.
Frequently asked questions
How is boiler size measured?+
Boiler size is measured in BTU/hr (British Thermal Units per hour) of heat output. The right size matches your home’s peak heat loss without being oversized.
What happens if my boiler is oversized?+
An oversized boiler short-cycles — turning on and off frequently — which wastes fuel, increases wear, and reduces comfort. Proper sizing is key to efficiency.
Should I get a professional heat-loss calculation?+
Yes. This calculator gives a fast estimate, but a certified installer should perform a full heat-loss (Manual J) calculation before final sizing.
Ready for the next step?
Get matched with approved local installers and real quotes.