BTU Heating Calculator
Single Room
Calculate BTU needed for one room
Whole Home
Calculate furnace/heating system size for entire home
Formula
BTU = Square Feet × Base BTU/sqft × Insulation Factor × Climate Factor | Furnace Size = BTU Load / AFUE Efficiency
Frequently Asked Questions
How many BTU per square foot do I need?
General guidelines by climate: Hot regions need 20-25 BTU/sq ft, moderate climates 30-40 BTU/sq ft, and cold climates 45-60 BTU/sq ft. Poorly insulated homes may need 40% more, while well-insulated homes need 20-35% less.
What size furnace do I need?
For a 2,000 sq ft well-insulated home in a cold climate: 2,000 × 45 × 0.8 = 72,000 BTU heating load. For an 80% AFUE furnace, you would need a 90,000 BTU input furnace. For a 95% AFUE, about 76,000 BTU input.
What is AFUE?
AFUE (Annual Fuel Utilization Efficiency) measures furnace efficiency. An 80% AFUE furnace converts 80% of fuel energy to heat. High-efficiency furnaces are 90-98% AFUE. The minimum federal standard is 80% for non-weatherized gas furnaces.
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