How to estimate heating capacity
Multiply conditioned floor area by an adjustable low and high BTU-per-square-foot factor for a rough range.
Before you buy
This is NOT a heating equipment sizing tool. Climate, insulation, windows, infiltration, ductwork, and building geometry require a qualified Manual J load calculation. Oversizing can reduce comfort and efficiency.
Can I select a furnace using this estimate?
No. Have a qualified professional perform a Manual J heating-load calculation.
Last reviewed: October 2026. This tool performs calculations locally in your browser.