Furnace BTU Sizing Calculator
Furnace Size by Square Footage
Estimate furnace BTU output needed for your home
Efficiency Comparison
Compare heating costs between furnace efficiency levels
Formula
Output BTU = Sq Ft x BTU/sqft x Insulation Factor x Ceiling Factor | Input BTU = Output / AFUE
Frequently Asked Questions
How many BTU do I need per square foot for heating?
It depends on your climate zone. In mild climates (Zone 1-2), you need 25-35 BTU per square foot. In moderate climates (Zone 3), 40-50 BTU. In cold climates (Zone 4-5), 50-60 BTU per square foot. These are output BTU values.
What size furnace do I need for a 2000 sq ft house?
In a moderate climate with average insulation, a 2,000 sq ft home needs approximately 90,000 BTU output, which translates to a 100,000-120,000 BTU input furnace at 80% AFUE efficiency. In cold climates, you may need a 120,000-140,000 BTU unit.
What does AFUE mean for furnaces?
AFUE (Annual Fuel Utilization Efficiency) measures what percentage of fuel is converted to heat. An 80% AFUE furnace converts 80 cents of every fuel dollar to heat; 20 cents goes up the flue. High-efficiency (96% AFUE) furnaces waste only 4 cents per dollar.
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