How it works
A space heater's cost depends on three things: its wattage, how long its heating element is actually on, and what you pay per kWh. A 1,500 W heater uses 1.5 kWh for every hour it runs at full power.
If the heater has a thermostat, the element switches off once the room is warm, so over a day it may run only half to three-quarters of the time. Pick the setting that matches your room; for a cold, draughty room, assume it runs on full.
The formula
kWh per hour = watts ÷ 1,000 × share of time on cost per hour = kWh per hour × price per kWh cost per month = cost per hour × hours a day × days a month
Worked example
A 1,500 W heater on full for 8 hours a day, 30 days a month, at the US average of 18.2¢ per kWh.
| Step | Working | Result |
|---|---|---|
| Per hour | 1.5 kWh × $0.182 | $0.27 |
| Per day | $0.273 × 8 h | $2.18 |
| Per month | $2.184 × 30 | $65.52 |
| Whole winter | $65.52 × 5 months | $327.60 |
Frequently asked questions
How much does it cost to run a 1,500 W space heater?
About $0.27 an hour at the US average of 18.2¢ per kWh, or about 39.5p an hour at the UK price cap rate of 26.32p. Eight hours a day for a month is roughly $66 in the US.
Is a space heater cheaper than central heating?
Only when it lets you heat one room and turn the rest of the house down. Per unit of heat, electric resistance heating usually costs more than a gas furnace or boiler, and two to four times more than a heat pump. Heating a whole home with space heaters is rarely cheaper.
Are oil-filled radiators cheaper to run?
No. Every electric heater turns electricity into heat at essentially 100%, so a 1,500 W oil-filled radiator costs the same per hour on full as a 1,500 W fan heater. Oil-filled models hold heat longer, which can make the thermostat cycle less often in a well-insulated room.
Does a lower setting save money?
Yes, in proportion: 750 W costs half as much per hour as 1,500 W. But if the room never reaches temperature on low, you may simply run it for longer.
Is it safe to leave a space heater on overnight?
Choose a heater with tip-over and overheat shut-off, plug it straight into a wall outlet (not an extension lead or power strip), and keep it at least 3 feet (1 metre) from bedding, curtains and furniture.
Sources
- Default prices: US average residential price, EIA 2026 forecast (checked Oct 2026); Ofgem price cap unit rate, 1 Oct – 31 Dec 2026, Direct Debit (VAT on electricity is 0% until 31 Mar 2027).
- US Department of Energy, portable heaters.
Related guides
Estimates are for planning only and are not financial advice. Get written quotes before you buy.