Heat Loss Calculator — Wall and Insulation R-Value Estimator
Calculate heat loss (BTU/hr) through a wall assembly and estimate the total effective R-value from multiple insulation layers, including air films and sheathing.
Wall Assembly Layers (R-values per layer)
Enter 0 to omit a layer. R-values are in °F·ft²·hr/BTU.
Formulas Used
Total R-Value (series resistances):
Rtotal = Rint-air + Rdrywall + Rinsulation + Rsheathing + Rext-finish + Rext-air + Rextra
U-Value (overall heat transfer coefficient):
U = 1 / Rtotal [BTU / (hr · ft² · °F)]
Heat Loss Rate:
Q = U × A × ΔT [BTU/hr]
Where A = wall area (ft²), ΔT = Tindoor − Toutdoor (°F)
Equivalent forms:
Q = (A × ΔT) / Rtotal