Heat Loss Calculator
Estimate building heat loss in BTU per hour based on envelope area, insulation R-value, and temperature difference.
Total Heat Loss (with infiltration)
11,538 BTU/hr
Total Heat Loss (with infiltration) vs Envelope Area (walls + ceiling)
Formule
## 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.
Exemple Résolu
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
Questions Fréquentes
What is a typical design temperature difference?
Use the outdoor design temperature for your area (available from ASHRAE data) subtracted from your desired indoor temperature (usually 70 degF). For example, if outdoor design is 5 degF, DeltaT = 65.
Should windows be calculated separately?
For accuracy, yes. Windows have much lower R-values (R-1 for single pane, R-3 for double). Calculate window and wall areas separately and sum the losses.
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