How Much Does It Cost to Run a Space Heater?
How to work out what a space heater costs per hour and per month from its wattage and your electricity rate, when it saves money, and when it quietly becomes the most expensive heat in the house.
- Cost = kilowatts × hours × your rate — a 1,500W heater run 8 hours a day is about $66 a month at the U.S. average rate.
- That's a ceiling, not the answer: a heater with a working thermostat cycles off, so real cost is often closer to $27 a month at a 40% duty cycle.
- A plug-in meter left in place for a few days is the only way to know your own duty cycle.
- A space heater only saves money when it lets you turn down central heat and warm just the room you're using.
- Plug directly into a wall outlet — never an extension cord or power strip — and keep three feet of clearance from anything flammable.
On this page
A space heater is one of the few appliances where the arithmetic is genuinely simple: there is no efficiency rating to argue about, because essentially all the electricity becomes heat. The part people get wrong is not the formula — it is assuming the heater runs flat out for every hour it is switched on.
The formula
Cost = kilowatts × hours × rate. Divide the nameplate watts by 1,000 to get kilowatts, multiply by hours to get kilowatt-hours, multiply by what you pay per kWh. A 1,500W heater is 1.5 kW.
| Run time | Energy used | Cost |
|---|---|---|
| 1 hour | 1.5 kWh | ≈ $0.28 |
| 8 hours/day | 12 kWh | ≈ $2.21/day |
| 8 hours/day for 30 days | 360 kWh | ≈ $66/month |
Nameplate wattage is a ceiling, not a consumption
That table assumes the element is energized every minute the heater is switched on. That is true of a heater with no thermostat, on its highest setting, in a room it cannot warm. It is not true of most real installations.
A heater with a thermostat behaves like any other thermostatic appliance: it runs at full power until the room reaches the setpoint, then cycles off and on to hold it. The share of time the element is actually on is the duty cycle, and it is what separates the ceiling from your bill.
How to measure what it actually uses
A plug-in energy meter sits between the outlet and the appliance and accumulates kilowatt-hours. It removes every assumption above, including the duty cycle, because it records what happened rather than what should have happened.
- Check the meter's rating before anything else. A 1,500W heater draws about 12.5 amps at 120 volts; many inexpensive meters are rated at 15 amps and some lower. Do not use one rated below the heater's draw.
- Plug the meter directly into a wall outlet, then the heater directly into the meter. No extension cord, no power strip, no second adapter in the chain.
- Read the cumulative kilowatt-hours, not the instantaneous watts. The watt reading only tells you the draw at that second, which for a cycling heater is either full power or almost nothing.
- Leave it in place for several days of normal use so the reading includes cold nights, mild nights, and every on-off cycle.
- Divide the total kWh by the number of days to get a daily average, then multiply by 30 and by your rate.
- Compare that against scenario A above. The ratio between them is your real duty cycle.
| 12¢/kWh | $43 | |
|---|---|---|
| 18.44¢/kWh (U.S. average) | $66 | |
| 25¢/kWh | $90 | |
| 35¢/kWh | $126 |
Scenario A: one 1,500W heater run 8 hours a day for 30 days = 360 kWh. Monthly cost = 360 × your rate. Find your rate on your bill — after duty cycle, it is the biggest variable here. Apply your own duty cycle to any of these bars. Arithmetic; rate range reflects the spread in EIA residential price data across U.S. states.
When a space heater actually saves money
There is exactly one scenario where it wins: you turn the central thermostat down meaningfully and heat only the room you are occupying. Zone heating like that can cost less than warming the whole house. Run the heater without touching the thermostat and you have simply added a load.
Will a space heater actually save you money?
Where the numbers change
- Duty cycle, first and above everything else — it is the difference between $66 and $27 in the example above.
- Your rate: a state at 12¢/kWh and one at 35¢ produce completely different answers from identical use.
- Room size, insulation and outdoor temperature, all of which act on the duty cycle rather than on the wattage.
- The setting used: many heaters offer a low setting at roughly half the nameplate wattage.
- Time-of-use plans, which can make evening running significantly more expensive than the average rate suggests.
What to do next
Take the wattage from the label and your effective rate from the most recent bill, and run scenario A for your real hours — that is your worst case. Then put a correctly rated meter on it for a week and find the real figure. If the monthly number still looks uncomfortable, the fix is usually air sealing and insulation in that cold room rather than more heating.
Sources
- Space Heaters — U.S. Department of Energy — Energy Saver. Consulted July 22, 2026.
- Electric Power Monthly, Table 5.6.A — average residential price by state — U.S. Energy Information Administration. Consulted August 1, 2026.
- Electric Power Monthly (residential electricity prices) — U.S. Energy Information Administration. Consulted July 22, 2026.
- Energy Saver: Save Energy, Save Money — U.S. Department of Energy. Consulted July 22, 2026.
Frequently asked questions
Are some space heaters cheaper to run than others?
At the same wattage and the same run time, no — electric resistance heaters are all roughly equally efficient at turning electricity into heat. What differs is the thermostat, the timer, and how well the heat reaches you, all of which change how many hours the element is actually energized.
Why does my heater cost less than the nameplate math suggests?
Because nameplate wattage is the draw while the element is on, not an average. A heater with a working thermostat reaches the setpoint and cycles off. Multiply watts by hours and you get the ceiling; the real figure is that ceiling multiplied by the duty cycle.
How do I find out what it actually uses?
Put a plug-in energy meter between the outlet and the heater, run it normally for several days, and read the cumulative kilowatt-hours — not the instantaneous watts. Divide by the number of days, then multiply by your rate. Check the meter's amp rating first: a 1,500W heater draws about 12.5 amps at 120 volts, close to the limit of many meters.
Is a space heater cheaper than central heating?
Only if it lets you lower the central thermostat and heat one occupied room instead of the whole house. Running one alongside unchanged central heat simply adds a 1,500W load to the bill.
Do infrared or 'eco' heaters use less electricity?
For the same wattage and run time they draw the same power. Infrared can feel warmer sooner because it heats objects and people directly, which may let you run it less — that is a usage saving, not an efficiency one.