The formula
Electricity is billed per kilowatt-hour (kWh) — one kilowatt drawn for one hour. So:
Cost per hour = (watts ÷ 1,000) × your price per kWh
Your price per kWh is printed on your electricity bill. Use your own figure rather than a national average — tariffs vary enormously between countries, suppliers and times of day.
A worked example
Take a 2,000 W heater and a tariff of 0.30 per kWh in whatever your currency is:
- 2,000 ÷ 1,000 = 2 kW
- 2 × 0.30 = 0.60 per hour
- Four hours an evening = 2.40 per evening
- Thirty evenings = 72 per month
Run the same sum with a 1,500 W unit and you get 0.45 per hour, 1.80 per evening and 54 per month. The wattage is doing all the work in that calculation, which is exactly why it is the number to insist on before buying.
Why the real figure is usually lower
A heater with a working thermostat does not draw full power continuously. It heats until the room reaches the set temperature, then cycles — drawing full power perhaps a third to a half of the time once the room is warm, depending on insulation and how cold it is outside.
So treat the figure above as the ceiling. The real monthly cost tends to land somewhere between a half and two-thirds of it. That is still the number to put against whatever you save by turning the central heating down — which, as we set out here, is the only way a plug-in heater saves anyone money.
Frequently asked questions
How much does a 1500 W heater cost per hour?
1.5 multiplied by your price per kWh. At 0.20 per kWh that is 0.30 an hour; at 0.35 per kWh it is about 0.53 an hour. Use the tariff on your own bill.
Does a thermostat reduce running cost?
Yes, meaningfully. Once the room reaches temperature the heater cycles rather than drawing full power continuously, often cutting real consumption to roughly half to two-thirds of the theoretical maximum.
Is it cheaper to run one big heater or two small ones?
Neither. Total cost follows total watts. Two 750 W heaters cost the same to run as one 1,500 W heater. Where two units help is coverage — warming two rooms at once — not price.
Sources
- Heatoor, WellHeater and VelaWarm product pages — checked 12 September 2026 for a published power rating; none found.