Before you begin
What affects room heater running costs
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
Understanding what each heater costs to run
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.
- Gas and oil central heating are priced from national average fuel prices through an 85% seasonal boiler efficiency, because the form does not ask what you pay for them. A heat pump is priced from the electricity rate you did enter, divided by a cautious seasonal factor of 3.
- 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.
Worked example
The same question, answered end to end
Heating one person for five hours in a 20 m² reasonably insulated room, in a house with mains gas central heating, on a 36c unit rate.
What was entered
- Warming one person, not the whole room.
- Five hours an evening in a 20 m² room with reasonable insulation.
- Mains gas central heating available as the alternative.
- Electricity at 36c per kWh.
How it is worked out
20 m² at 75 W/m² means the room loses about 1.5 kW, which is what a heater would have to replace to warm the room.
Warming one person directly does not have to replace that: a 100 W heated throw is enough.
100 W for five hours is 0.5 kWh, which is 18c at 36c per kWh.
Over 150 evenings that is about €27 for the winter.
The same five hours on the gas boiler is priced at its own cost per useful kWh, so the comparison is against the real alternative rather than against another plug-in heater.
What the tool returns
- Heat this room needs
- 1.5 kW
- Power the pick draws
- 100 W
- Cost per evening
- €0.18
- Cost for the winter
- €27
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.