Before you begin
What this tool needs
Measure length by width for a rough room area.
Choose ‘the whole room’ only when the air and the surfaces need to be warm, not simply one seated person.
Reading the answer
What your result means
A heater marked as too small only looks cheaper because it cannot keep up with the heat the room loses.
Any heater with a thermostat that can keep up costs broadly the same to run; speed, silence and comfort decide between them.
Boundaries
Assumptions and limitations
Working assumptions
- The room is modelled as losing 55, 75 or 110 watts for every square metre of floor.
- A winter is 150 heating evenings.
- Infrared gets a restrained 15% allowance for warming people directly rather than the air.
Where to be careful
- Ceiling height, glazing, wind exposure and outdoor temperature are not modelled.
- Never cover a room heater or use an indoor unflued gas heater. Follow the manufacturer’s safety instructions.
Common questions
Questions about this tool
Is an oil-filled radiator cheaper than a fan heater?
For the same room heat delivered at the same electricity rate, broadly no. A thermostat, room heat loss and time used determine the energy.
Why is a heated throw so much cheaper?
It warms one body at roughly 100 W instead of replacing heat lost from an entire room at perhaps 1–3 kW.