What a 3 kW heater costs, by electricity price
A 3 kW heater is the most a heater on a standard 13 A plug can draw, so it is the largest plug-in heater sold. It uses 3 kWh for every hour at full power. Unit rates change with each price cap and tariff, so find yours on your bill and use the nearest row, or enter it in the electricity cost calculator. These are energy costs only: the daily standing charge is paid whatever you use.
| Unit rate | Per hour | Per 8-hour day | Per month (4 h a day) | Per month (8 h a day) |
|---|---|---|---|---|
| 24p per kWh | £0.72 | £5.76 | £86.40 | £172.80 |
| 27p per kWh | £0.81 | £6.48 | £97.20 | £194.40 |
| 30p per kWh | £0.90 | £7.20 | £108.00 | £216.00 |
With a thermostat
A heater with a thermostat switches off when the room reaches temperature, so it averages less than its rating. Four hours a day at 27p per kWh:
| How it runs | Per hour | Per day | Per month |
|---|---|---|---|
| Flat out (no thermostat) | £0.81 | £3.24 | £97.20 |
| Thermostat, cold room | £0.61 | £2.43 | £72.90 |
| Thermostat, cycling about half the time | £0.41 | £1.62 | £48.60 |
Plugs, fuses and safety
At 13.0 A a 3 kW heater uses almost the whole of a 13 A plug's fuse, so plug it straight into a wall socket, never into an extension lead or an adaptor with other things on it. It warms a room quickly, but it is the most expensive way to heat a room for hours.
Never leave a heater on unattended or overnight, and keep it clear of curtains, bedding and clothes. The appliance running cost guide compares heaters with other appliances, and the radiator size calculator works out the heat any room needs.
Want to change anything else? The calculator above is the full Electricity Cost Calculator (UK): edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
How much does it cost to run a 3 kW heater per hour?
£0.81 an hour at 27p per kWh, if it runs flat out. A 3 kW heater uses 3 kWh every hour. With a thermostat that cycles it off half the time, the cost falls to about £0.41 an hour.
How much does a 3 kW heater cost to run a month?
£97.20 a month for 4 hours a day at 27p per kWh, or £194.40 for 8 hours a day, both flat out. That is 360 kWh or 720 kWh a month.
How big a room will a 3 kW heater heat?
About 22.5 m² of living room kept at 21°C, or 25.5 m² of bedroom at 18°C, with a 2.4 m ceiling, double glazing, one external wall and filled cavity walls. A cold, solid-walled room needs more.
Related sizes and guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.