How to Calculate the Required BTU
The following calculation is based on a standard boiler heating system (ΔT50)
Metric (metres)
Measure the length, width and ceiling height of the room in metres.
Calculate the room volume:
length × width × height = room volume (m³)
Estimate the required heat output:
Average insulation:
room volume (m³) × 170 = required BTU
Good insulation:
room volume (m³) × 136 = required BTU
Imperial (feet)
Measure the length, width and ceiling height of the room in feet.
Calculate the room volume:
length × width × height = room volume (ft³)
Estimate the required heat output:
Average insulation:
room volume (ft³) × 4.8 = required BTU
Good insulation:
room volume (ft³) × 3.85 = required BTU
This provides a quick estimate of the radiator heat output required for a room with average or good insulation.
Low-temperature heating systems may require a different calculation.
For a precise heat loss calculation, consult a qualified heating engineer, especially for low-temperature heating systems (such as condensing boilers and heat pumps) where accurate sizing is essential.
