As an Amazon Associate I earn from qualifying purchases. Links to Amazon on this page are affiliate links.
What a space heater uses per hour, in kWh
Updated
A 1,500 watt heater running at full power uses 1.5 kilowatthours every hour. Eight hours is 12 kWh. Multiply that by the rate on your own power bill to get your cost. We do not print a cost here, because rates differ a lot from place to place and change over time. The calculator will do the multiplication with your rate.
The formula
The EIA explains that a watthour is one watt used for one hour, a kilowatt is 1,000 watts, and utilities bill in kilowatthours. So:
kWh = watts x hours / 1,000, and cost = kWh x your rate per kWh.
| Heater and setting | Watts | kWh per hour | kWh for 8 hours | kWh for 30 days at 8 hours |
|---|---|---|---|---|
| Full-size heater on high | 1,500 W | 1.5 | 12 | 360 |
| Amazon Basics Ceramic 1500W on low | 900 W | 0.9 | 7.2 | 216 |
| Lasko MyHeat 101 | 200 W | 0.2 | 1.6 | 48 |
- Full-size heater on high12 kWh
- Amazon Basics on low (900 W)7.2 kWh
- Lasko MyHeat (200 W)1.6 kWh
Find your rate on your bill. It is usually shown in cents per kWh. If your bill shows 15 cents, then 12 kWh is 12 x 15 = 180 cents for an eight hour day at full power. That is only an example of the arithmetic. Use your own number.
No plug-in heater is more efficient than another
Electric resistance heaters turn essentially all the power they draw into heat. One kilowatthour gives 3,412 Btu per the EIA, in a ceramic cube or an infrared cabinet alike. So an "energy saving" heater cannot make more heat from the same kWh. It can only use fewer kWh by running less or at lower power. Three things do that:
- A thermostat. Once the room reaches the set point the element cycles off. If it is on half the time, 8 hours uses about 6 kWh instead of 12. How often it cycles depends on your room, which is why the table above is a ceiling and not a forecast.
- A lower setting. The Amazon Basics Ceramic 1500W states 900 watts on low. The De'Longhi EW7707CM has three heat settings. De'Longhi claims up to 20 percent savings for its ComfortTemp button, and its own footnote says that is compared with running the same heater with the thermostat at maximum. That is a fair way to read every eco mode: it saves against leaving the heater flat out.
- Heating less space. Close the door. A heater sized for the room you are in, with the rest of the home set a little cooler, is the case where a space heater can lower a bill. Heating the whole home with plug-in heaters usually does the opposite.
Warming a person is the cheapest option
The 200 watt Lasko MyHeat 101 uses 1.6 kWh in eight hours, against 12 for a full-size heater on high. It will not warm a room. If all you need is warm feet at a desk, that gap is the whole argument for it.
Size matters more than the brand
If your room needs more than 1,500 watts, the heater never reaches its set point, never cycles off, and uses the full 1.5 kWh every hour while the room stays cool. Check the room first with the calculator.
Check your own room with the size and power use calculator, or compare all seven picks on the roundup page.
Safety note: keep any heater at least three feet from anything that can burn, plug it straight into a wall outlet, and turn it off when you leave the room or go to sleep. See the safety rules. This site is not electrical advice. If an outlet or plug gets warm, stop using it and ask a licensed electrician.