How it works
An electric space heater turns electricity directly into heat, so its running cost depends on only three things: how many watts it draws, how many hours it runs and what you pay per kilowatt-hour (kWh). A kilowatt-hour is 1,000 watts used for one hour.
kWh per day = watts ÷ 1,000 × hours per day × share of time on
cost per day = kWh per day × price per kWh · cost per month = cost per day × days
The "share of time on" field accounts for the thermostat. Once a room warms up, a heater with a thermostat switches its element on and off. If it heats only half the time, it uses half the energy.
Worked example
A 1,500 W heater on full power for 8 hours a day uses 1.5 × 8 = 12 kWh per day. At an example rate of $0.15 per kWh, that is $1.80 a day, or about $0.23 an hour. Over 30 days it uses 360 kWh and costs $54.00.
If the thermostat keeps the element on only half the time, the same heater uses 6 kWh a day and costs $0.90 a day, or $27.00 a month.
Cost per hour by heater setting
| Setting | kWh per hour | At $0.15/kWh | 8 hours a day |
|---|---|---|---|
| 750 W (low) | 0.75 | $0.11 | $0.90 |
| 1,000 W | 1 | $0.15 | $1.20 |
| 1,500 W (high) | 1.5 | $0.23 | $1.80 |
How your rate changes the bill
Electricity prices vary widely by region, season and plan. The same 1,500 W heater, 8 hours a day for 30 days:
| Price per kWh | Monthly cost |
|---|---|
| $0.10 | $36.00 |
| $0.15 | $54.00 |
| $0.20 | $72.00 |
| $0.30 | $108.00 |
Find your rate by dividing the energy charges on your bill by the kWh used. If you have time-of-use pricing, use the rate for the hours the heater runs.
Are some heaters cheaper to run?
No electric resistance heater is more efficient than another. Oil-filled radiators, ceramic heaters, infrared heaters and fan heaters all turn each kWh into the same 3,412 BTU of heat. A 1,500 W heater of any type gives about 5,118 BTU/hr. What differs is how the heat reaches you: radiant and infrared models warm people and objects in front of them, while fan heaters warm the air faster. Running cost comes from watts and hours, not the label. To compare with central heating, see space heater vs. furnace cost.
Is one heater big enough for the room?
A common rule of thumb for electric heat is about 10 watts per square foot of floor in an average room. By that rule a 1,500 W heater can be the main heat for roughly 150 sq ft, or supplement a larger room that already gets some central heat. Cold climates, high ceilings and drafty rooms need more. For a better estimate based on your climate and insulation, use the heating BTU calculator and divide its BTU/hr result by 3.412 to get watts.
Ways to spend less
- Heat only the room you are in and close its door, then turn down the central thermostat.
- Use the low setting and the thermostat rather than full power all day.
- Stop drafts at windows and doors first. Less heat loss means the heater cycles off more.
- Use a timer so the heater does not run in an empty room.
Space heater safety
- Plug the heater directly into a wall outlet. Do not use an extension cord or power strip.
- A 1,500 W heater draws 12.5 amps at 120 volts, most of a typical 15-amp circuit. Avoid running other large loads on the same circuit.
- Keep anything that can burn, such as bedding, curtains and paper, at least 3 ft (1 m) away.
- Choose a heater with tip-over and overheat shut-off, listed by a recognized testing lab.
- Turn it off when you leave the room or go to sleep, and keep working smoke alarms.
Frequently asked questions
How much does it cost to run a 1,500 W space heater for 24 hours?
It uses 36 kWh on full power. At $0.15 per kWh that is $5.40 a day. Multiply 36 by your own rate for your figure.
How many kWh does a space heater use per hour?
A heater uses its wattage divided by 1,000 each hour it runs at full power: 1.5 kWh for a 1,500 W heater and 0.75 kWh on a 750 W low setting.
Do space heaters use a lot of electricity?
Compared with most household appliances, yes. A 1,500 W heater running 8 hours uses 12 kWh a day, about as much as an efficient modern refrigerator uses in a week or more.
Is an oil-filled heater cheaper to run?
Not per hour at the same wattage. All electric resistance heaters convert power to heat at the same rate. An oil-filled model may cycle a little more evenly, but watts and hours set the cost.