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

Assumptions & References

In the network