Heat Loss Calculator
Estimate room heat loss from wall, window, ceiling, floor and air-infiltration inputs in imperial or metric units.
Default project preview
8,923 BTU/h
Envelope transmission
6,168 BTU/h
Air infiltration
1,944 BTU/h
Temperature difference
50 °F
Room volume
4,320 ft³
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Transmission loss = area × U-factor × temperature difference for each surface. Infiltration uses room volume × air changes × air heat-capacity factor. Design reserve is applied last.
FAQ
Heat Loss Calculator questions
What is a U-factor?+
U-factor describes heat flow through an assembly; lower values generally mean better insulation.
Why does infiltration matter?+
Outdoor air entering through leakage or ventilation must be heated, adding to the design load.
Can this select a furnace or heat pump?+
No. Equipment selection requires a complete building load calculation and performance data at design conditions.