Explore your home’s heat loss

Furnace size calculator

Build an illustrative 3D model of your home and explore a whole-home, steady-state heating-load estimate. Enter your heated area and select construction assumptions in Basic mode, or refine measured inputs in Advanced mode. Review which components contribute to heat loss and compare improvements using the same calculation.

Choose a city and review the climate reference, its coverage and design temperature. The tool shows its assumptions, keeps heating load separate from furnace output and lets you save projects in this browser. Construction choices are scenarios, not measurements of your home.

This is a screening estimate, not a certified Manual J calculation or an instruction to buy a particular furnace. Confirm final equipment sizing with a qualified HVAC professional.

Read the methodology, sources and limitations.

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