A space heater warms one room without heating the whole house, which makes it useful for a cold office, a basement or a drafty bedroom. Choosing one is mostly about the room, how you'll use it, and safety, because every electric model turns electricity into heat at the same rate.
Most plug-in electric space heaters top out at 1,500 watts, about 5,100 BTU per hour, and cost about 27 cents an hour at 18 cents per kWh. All electric resistance types are equally efficient; choose by how they deliver heat, and look for safety certification, tip-over shutoff and overheat protection.
Types of electric space heaters
The three common designs deliver the same heat per watt but feel different in a room. Match the type to how you use the space rather than to any efficiency claim.
| Type | Warm-up speed | Noise | Heat retention | Best for |
|---|---|---|---|---|
| Oil-filled convection radiator | Slow | Silent | Holds warmth after it cycles off | A room you occupy for hours, bedrooms |
| Ceramic or fan-forced | Fast | Some fan noise | Cools quickly once off | Quick warm-up of a room you enter and leave |
| Radiant or infrared | Immediate on what it faces | Silent, no fan | None stored, warmth stops when off | Spot-heating a person in a drafty or open space |
Each turns essentially all its electricity into heat, so the difference is comfort and speed, not cost per hour at the same wattage.
Sizing
A 1,500-watt heater delivers about 5,100 BTU per hour (1,500 × 3.412). Every watt becomes the same heat, so a heater's output scales straight with its setting:
| Heater setting | Heat output (watts × 3.412) |
|---|---|
| 500 W | about 1,700 BTU/hr |
| 750 W | about 2,560 BTU/hr |
| 1,000 W | about 3,410 BTU/hr |
| 1,250 W | about 4,270 BTU/hr |
| 1,500 W | about 5,100 BTU/hr |
To turn that into a room size, compare the output to how fast the room loses heat. At a cold-night design low near 10°F, the site heat-loss model puts a room's loss at about 11 BTU/hr per sq ft for current-code and 2000s construction, about 16 for a 1980s or 1990s home, and about 36 for a drafty pre-1970 room (see the furnace sizing calculator). Dividing one 1,500-watt heater's 5,100 BTU/hr by those rates, a single heater holds roughly 460 sq ft of newer space (5,100 ÷ 11), about 320 sq ft of 1980s or 1990s space (5,100 ÷ 16), or about 140 sq ft of drafty older space (5,100 ÷ 36).
A room sharing walls with heated space loses less, and milder weather needs less, so treat those areas as coverage at a cold design low rather than a hard limit. A cold, drafty or large room can exceed what one heater delivers, which points to a permanent solution such as a ductless heat pump; see how many mini splits you need.
Running cost
Cost = watts × hours ÷ 1,000 × your rate: a 1,500-watt heater costs about 27 cents an hour at 18 cents per kWh, about $65 a month at 8 hours a day. See electric heater running cost for more examples and a calculator.
Features that affect comfort and cost
Beyond safety, a few features change how pleasant and how cheap a heater is to live with. Look for these when you buy:
- An adjustable thermostat, so the heater cycles off at temperature instead of running at full power, which lowers running cost.
- More than one wattage setting, such as 750 W and 1,500 W, so you can drop to the lower step and use half the electricity.
- A timer or programmable schedule, so it isn't heating an empty room.
- Quiet operation for a bedroom or office; oil-filled and infrared types run without a fan.
Safety features to look for
- Certification by a nationally recognized testing laboratory.
- Tip-over shutoff, which turns the heater off if it's knocked over.
- Overheat protection, which shuts it off if internal parts get too hot.
- A thermostat, so it cycles instead of running at full power.
Using a space heater safely
- Plug it directly into a wall outlet, not an extension cord or power strip; a 1,500-watt heater draws 12.5 amps.
- Keep it at least 3 feet from bedding, curtains, furniture and anything else that can burn (CPSC guidance).
- Place it on a hard, level floor, away from foot traffic.
- Turn it off when you leave the room or go to sleep, unless it's designed for unattended use.
Gas and kerosene heaters
Fuel-burning heaters make heat by combustion, which consumes oxygen and releases water vapor, carbon dioxide and carbon monoxide into whatever space they vent to. A unit labeled for outdoor use only, such as a patio or construction heater, must never run indoors, because it has no provision to limit indoor carbon monoxide. Only a heater specifically rated for indoor use belongs in a living space, and even then only with the ventilation its instructions require.
Unvented indoor models draw room air for combustion and send their exhaust back into the room, so they depend on fresh-air ventilation and a working carbon monoxide alarm. Follow the heater's instructions on room size and airflow, respect any limits on bedrooms and closed rooms, and keep a CO alarm on every level; see the carbon monoxide detector guide.
When a heat pump makes more sense
The DOE notes that heat pumps can cut electricity used for heating by about half compared with electric resistance heat. For a room you heat every day, a ductless heat pump's lower running cost usually outweighs its higher price.
Put in numbers, the roughly $65 a month a 1,500-watt heater costs at 8 hours a day and 18 cents per kWh would fall to about $33 if a heat pump did the same job on about half the electricity (65 ÷ 2). That gap widens the more hours you heat, which is why a daily-use room favors the heat pump; electric heater running cost works the per-hour, per-day and per-month numbers for your own rate.
Frequently asked questions
What is the most efficient space heater?
All electric resistance space heaters are equally efficient at turning electricity into heat. Choose by how they deliver heat and by safety features.
How much does it cost to run a space heater?
About 27 cents an hour for a 1,500-watt heater at 18 cents per kWh.
Can a space heater heat a whole room?
A small to medium, insulated room, yes, as supplemental heat. Large or drafty rooms may need more than one heater can deliver.
Is it safe to leave a space heater on overnight?
Only if it's designed for unattended use, has tip-over and overheat shutoff, and is at least 3 feet from anything that can burn. Otherwise, turn it off.
What size space heater do I need for 500 sq ft?
A 500 sq ft room needs more heat than one standard 1,500-watt heater can supply at a cold design low. A well-insulated room that size loses roughly 5,500 BTU/hr on a cold night (500 × about 11 BTU/hr per sq ft from the site heat-loss model), above a 1,500-watt heater's 5,100 BTU/hr. One heater can take the edge off, but a room that size heated daily is better served by a permanent system; see how many mini splits you need.
Are infrared heaters better than ceramic?
Neither is more efficient at the same wattage, since both turn essentially all their electricity into heat. Infrared warms the people and objects it faces, which suits spot heating in a drafty or open space, while a ceramic fan-forced heater warms the room's air faster and more evenly. Choose by how you use the room, not by efficiency.
Do space heaters use a lot of electricity?
A 1,500-watt heater uses 1.5 kWh every hour, about 27 cents at 18 cents per kWh and roughly $65 a month at 8 hours a day. Run that way it draws about 360 kWh a month (1.5 × 8 × 30), more than 40% of a typical U.S. home's 863 kWh a month (EIA). One heater used briefly is cheap, while heating for long hours, or running several, adds up fast.
Sources & References
- U.S. DOE: Energy Saver Guide (PDF), heat pumps vs. electric resistance heating
- U.S. EIA: Electric Power Monthly (residential prices)
- U.S. EIA: Electric Sales, Revenue, and Average Price (average residential use, 863 kWh/month)
- CPSC: Space Heater Safety (keep at least 3 feet from anything that can burn)