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The short answer
An electric heater turns each kWh of electricity into one kWh of heat, so heat costs 26.32p per kWh. A gas boiler at 85% efficiency makes heat for about 9.4p per kWh. So the same warmth costs roughly three times as much from an electric heater.
When an electric heater makes sense
If you only need one room warm, say you work from home in a small office, a heater only heats that room. Central heating warms the whole house, including rooms nobody is in.
As a rough rule: if the room you're heating is less than about a third of your home's heated space, a heater can work out cheaper for those hours. If you'd be heating most of the house anyway, central heating wins.
What a heater costs per hour
| Heater | Typical power | Per hour at full power |
|---|---|---|
| Electric blanket | 130–200 W | 4.3p |
| Small oil-filled radiator | 1,500 W | 39p |
| Oil-filled radiator | 2,000 W | 53p |
| Fan heater / electric fire | 2,000–3,000 W | 66p |
Most heaters have a thermostat, so once the room is warm they switch on and off and cost less than the full-power figure.
Cheaper ways to stay warm
- An electric blanket costs about 4.3p an hour, a fraction of any heater.
- Turning your central heating down by a degree and closing doors to unused rooms often saves more than switching to a heater.
- Use the thermostatic valves on radiators to turn down rooms you don't use.
Sources: National Energy Action, Government in-situ boiler study, Ofgem price cap via Uswitch, Octopus Energy tariff data.