Heater Power Calculator
Free toolBefore buying a heater, calculate how many watts you need based on the room dimensions, its insulation, and the local climate.
Result
How to use it
- Enter the length, width and height of the room.
- Choose the insulation level: good, average or poor.
- Choose your climate and read the recommended power in watts.
What it works out and how
Power is worked out from the room volume, not just its floor area: 40 W per cubic metre with good insulation, 50 with average insulation and 60 if it is poor. The result is multiplied by 0.9 in a temperate climate and by 1.15 in a cold one. A 4 × 3 m room with a 2.5 m ceiling and average insulation in a cold climate needs about 1,725 W.
Frequently asked questions
Why volume rather than square metres?
Because it is the air that gets heated. A room with a 3-metre ceiling needs 20% more than the same floor plan with a 2.5-metre ceiling.
How do I know what insulation I have?
Double glazing and an insulated facade count as good. Single glazing, draughts or outer walls cold to the touch count as poor.
Should I buy more power than calculated?
A small margin helps heat up faster, but consumption depends on power and hours: a thermostat prevents the extra spend.