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Is one 1,500 watt heater enough for your room?
Updated
Enter your room. The calculator estimates the watts the room needs and checks that against 1,500 watts, the top setting on nearly every plug-in heater. Then it turns your hours into kilowatthours, the unit on your power bill. Type in your own rate if you want a cost. We do not guess it for you.
Space heater size and power use calculator
An estimate. The 6 and 8 watts per square foot come from Cadet's sizing article (1,500 W for a 250 sq ft room with central heat, 2,000 W with no other heat). The insulation and ceiling steps are ours. Power use assumes the heater runs at full power the whole time. A thermostat that cycles off will use less.
Where the numbers come from
- Watts per square foot. Cadet, a maker of electric heaters, says a 1,500 watt heater is right for a 250 sq ft room that already has central heat, and that the same room with no other heat needs 2,000 watts. That is 6 and 8 watts per square foot. We use those two figures.
- Ceiling. Cadet says higher ceilings mean more air to heat and tells you to move up in wattage. It gives no number. We scale by ceiling height divided by 8. That step is our estimate.
- Insulation. Our estimate: 15 percent less for a tight room, 25 percent more for a drafty one. A garage in a cold climate can need far more than this.
- Power use. The EIA defines a watthour as one watt used for one hour, and a kilowatt as 1,000 watts. So watts times hours, divided by 1,000, is kWh. A 1,500 watt heater running flat out uses 1.5 kWh every hour, and at the EIA figure of 3,412 Btu per kilowatthour that is 5,118 BTU per hour of heat.
Worked examples
| Room | Watts needed | Can one plug-in heater cover it? |
|---|---|---|
| 10 x 12 ft bedroom (120 sq ft), has central heat, average insulation | 750 W | Yes. About 50 percent of one 1,500 W heater |
| 12 x 14 ft bedroom (168 sq ft), has central heat, average insulation | 1,050 W | Yes. About 70 percent of one 1,500 W heater |
| Same 168 sq ft room, drafty, heater is the only heat | 1,700 W | No. About 200 W past the ceiling |
| 250 sq ft living room, has central heat, average insulation | 1,500 W | Yes. About 100 percent of one 1,500 W heater |
| 250 sq ft room with a 10 ft ceiling, has central heat | 1,900 W | No. About 400 W past the ceiling |
| 400 sq ft open living area, has central heat | 2,400 W | No. About 900 W past the ceiling |
| 400 sq ft garage, poor insulation, heater is the only heat | 4,000 W | No. About 2,500 W past the ceiling |
- 120 sq ft bedroom top-up750 W
- 168 sq ft bedroom top-up1,050 W
- 168 sq ft drafty only heat1,700 W
- 250 sq ft top-up1,500 W
- 400 sq ft top-up2,400 W
- 400 sq ft garage only heat4,000 W
Take the 12 x 14 bedroom. 168 sq ft x 6 = 1,008 watts, rounded up to 1,050. One heater covers that with room to spare. Now make the same room drafty and take away the central heat: 168 x 8 x 1.25 = 1,680, rounded up to 1,700. That is past the ceiling, and a heater whose listing claims 576 sq ft has exactly the same 1,500 watts to throw at it as one that claims 150.
What to do with the answer
- Under about 1,000 watts: any full-size pick will cycle on its thermostat. A stated low setting helps. The Amazon Basics Ceramic 1500W lists 900 watts on low, and the De'Longhi EW7707CM has three power levels.
- 1,000 to 1,500 watts: one heater will do it but will run most of the time. A good thermostat matters here. The DREO Atom One sets by single degrees.
- Over 1,500 watts: one plug-in heater will not hold the room. Close the door and heat a smaller space, fix the drafts, or ask an electrician about fixed heating on its own circuit. Do not put two heaters on one circuit. See heaters and breakers.
- Just you at a desk: the 200 watt Lasko MyHeat 101 warms a person, not a room.
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.