This furnace size calculator, or furnace BTU calculator, will help you determine what size of furnace you need for any room area, insulation type, or outdoor temperature.

Jun 3, 2025 · This furnace size calculator uses your house size, climate (see the map below) and other important information to tell you what size furnace your home needs to keep it warm …

Dec 22, 2025 · Use our free tool furnace size calculator to determine the right furnace BTU for your home based on square footage, climate, and insulation.

Easily find the right furnace size for your home with our free online Furnace Size Calculator. Quick BTU estimate by square footage and climate zone.

Calculate your ideal furnace size with our ASHRAE-based tool. Estimate BTU and heat loss, factoring in insulation, climate, and more. Save results as PDF!

Calculate the right furnace size for your home with our free Furnace Size Calculator. Enter your home measurements and get instant furnace size recommendations.

You can freely use the calculator to roughly estimate the capacity of a furnace you need. Use this map to determine the climate zone (or climate region) you’re living in: