Free Heat Loss Calculator
Estimate building heat loss in BTU per hour based on envelope area, insulation R-value, and temperature difference.
sq ft
degF
Total Heat Loss (with infiltration)
11,538 BTU/hr
Conductive Loss9,615 BTU/hr
Estimated Furnace Size20,000 BTU/hr
Total Heat Loss (with infiltration) vs Envelope Area (walls + ceiling)
Building Heat Loss
Q = (A / R) x DeltaT x Infiltration Factor
A is the total building envelope area through which heat escapes, R is the insulation R-value, and DeltaT is the temperature difference between inside and outside. The infiltration factor (1.1 to 1.5) adds losses from air leakage.
Example Calculation
2,500 sq ft envelope, R-13, 50 degF difference, 1.2 infiltration.
- 01Conductive = 2500 / 13 x 50 = 9,615 BTU/hr
- 02With infiltration = 9,615 x 1.2 = 11,538 BTU/hr
- 03Furnace size = round up to 20,000 BTU/hr
Frequently Asked Questions
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