About the Heating Load Calculator
Heating load for a home from floor area, insulation standard and design temperatures.
Also known as: boiler size calculator, heat pump sizing, heating kw calculator, radiator sizing.
How to use this calculator
- Enter total floor area, average ceiling height, building standard, indoor design temperature and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
load = area × specific load × ΔT ÷ design ΔT + hot water
Worked example
Using the values pre-filled in the calculator above:
- Total floor area = 120 m²
- Average ceiling height = 2.4 m
- Building standard: Average (70 W/m²)
- Indoor design temperature = 21 °C
- Outdoor design temperature = -2 °C
- Hot water allowance = 3 kW
the calculator returns:
- Heating load: 11.4 kW
- Space heating: 8.4 kW
- Hot water allowance: 3 kW
- In BTU/hour: 38,898