Use our heat output calculator to calculate the energy requirement of your room (in kW and BTU). This will give you the wood burning stove output required in kW or the BTU output needed for radiators connected to gas central heating. All dimensions are in metres.
Insulation levels in houses have improved dramatically over the years so the calculator is best for houses built before 1976. In 1976 Building Regulations changed to require minimum levels of insulation and every decade they have been tightened further. For a more detailed figure based on your own house construction use the more specialist Great Home Radiator Sizing Guide And BTU Calculator (link opens in separate tab of your browser).
Heat output calculator
How is the heat output calculated?
It measure (in metres) the length, width and height of the room and then multiplies these to get the volume of air in the room in cubic metres. An adjustment factor is then applied to allow for different levels of insulation. Four different adjustment factors are used:
- 10 for an extremely draughty room with maybe 2 outside walls and windows and doors that have no double glazing
- 15 for a reasonably insulated room with double glazing built before 1976
- 20 for a room built between 1976 and 1995.
- 25 for a room built after 1995.