Heat Loss Calculator
Design heat loss of a room or building through walls, windows, roof and floor plus ventilation air.
Inputs
m²
W/m²K
m²
W/m²K
m²
W/m²K
m²
W/m²K
m³
1/h
°C
°C
Results
- Total heat loss
- 2.17 kW
- Total heat loss
- 7,397 BTU/h
- Fabric loss
- 1,417 W
- Ventilation loss
- 751 W
Formula
Fabric = Σ (A × U) × ΔT
Ventilation = 0.33 × ACH × Volume × ΔT
ΔT = indoor − outdoor design temperature
Assumptions & limits
- Steady-state method (similar to EN 12831 simplified); thermal bridges are not included.
- 0.33 Wh/m³K is the volumetric heat capacity of air.
- Ground floors often use a lower effective ΔT; this tool applies the full ΔT.
Worked example
ΣAU = 18 + 14 + 10 + 12.5 = 54.5 W/K × 26 = 1,417 W; ventilation 0.33 × 0.7 × 125 × 26 = 751 W → 2.17 kW.