Space Heater Size for a Bedroom, by Square Foot

For a typical bedroom, a 1,500-watt space heater is the right size. The standard rule is 10 watts per square foot, so a 1,500-watt heater can heat about 150 square feet on its own, and most bedrooms are smaller than that.

Also, 1,500 watts is the most a regular wall outlet can safely run, so for most people the real question isn’t which size to buy. It’s whether your room has something that breaks the rule, such as tall ceilings, old windows, or a floor over a cold garage. This guide was updated October 15, 2026, as the first cold nights of fall arrive.

How many watts does a bedroom space heater need?

Multiply your bedroom’s square footage by 10 to get the wattage you need. A 10 by 12 bedroom is 120 square feet, so it needs about 1,200 watts to stay warm with the space heater as its only heat.

The rule assumes 8-foot ceilings, reasonable insulation, and a heater doing all the work. If you think in BTUs, one watt of electric heat equals about 3.41 BTUs per hour, so a 1,500-watt heater puts out roughly 5,100 BTUs per hour.

Electric heaters turn almost all of their electricity into heat. That’s why the label wattage tells you nearly everything about how much heat you get, and fancy names on the box don’t change that number.

What size heater fits common bedroom sizes?

A single 1,500-watt heater with a low setting covers nearly every standard bedroom. Here’s how the 10-watts rule works out for common room sizes with 8-foot ceilings.

Bedroom size	Square feet	Watts needed as main heat	What to buy
9 x 10 ft	90	900	1,500-watt heater, usually run on low
10 x 12 ft	120	1,200	1,500-watt heater
12 x 12 ft	144	1,440	1,500-watt heater
12 x 14 ft	168	1,680	1,500-watt heater if the house has other heat
14 x 16 ft	224	2,240	One heater for extra warmth only, or two on separate circuits

Don’t buy a smaller heater for a small room to save power. A 1,500-watt model with a thermostat will cycle off or drop to its low setting (often 750 or 900 watts) once the room is warm, and it reaches that temperature faster.

When does a bedroom need more heat than the rule says?

Add heat for anything that lets warmth escape or increases the air in the room. Tall ceilings are the most common one, because you’re heating volume and not only floor space.

For a 10-foot ceiling, multiply your number by 1.25. For a vaulted ceiling, use the average height, and remember the warm air will collect up near the peak and not where you sleep.

Other reasons to add 10 to 20 percent are single-pane windows, two or more outside walls, a room over a garage or crawl space, and a basement bedroom. If your windows sweat on cold mornings, that tells you a lot of heat is leaving through the glass, and our guide on stopping condensation on the inside of windows covers the cheap fixes that help with both problems.

The opposite is also true. If the furnace keeps the house around 64 degrees and you want the bedroom at 68, the heater only has to make up a few degrees, and you might need half the wattage the chart shows or less.

Can one space heater warm a large bedroom?

One 1,500-watt heater can take the chill off a large bedroom, but it can’t be the only heat in a room much bigger than 150 square feet. No standard plug-in heater goes higher, because a 1,500-watt heater already draws about 12.5 amps on a 120-volt circuit.

Most bedroom circuits are 15 amps, and they often also run lamps, a TV, and phone chargers. Two heaters on the same circuit will trip the breaker, or worse, so if you need two, put them on separate circuits.

For a large primary bedroom that’s always cold, two heaters are a stopgap. Fixing the drafts, adding a rug over a cold floor, or having an electrician install a hardwired 240-volt wall heater is the better long-term fix.

Which type of heater works best in a bedroom?

For most bedrooms, an oil-filled radiator or a ceramic heater with a thermostat is the right type. All 1,500-watt heaters put out about the same heat, so the type changes how the heat feels and sounds, not how much you get.

Oil-filled radiators are silent, have no glowing elements, and keep giving off heat after they cycle off. They take 20 minutes or more to warm a room, so turn one on well before bed.

Ceramic fan heaters warm a room in a few minutes, but the fan makes noise and blows dry air. If you run one a lot, dry air is common, and a humidifier helps as long as you keep it clean (here’s how to get pink mold out of a humidifier when it starts to build up). Infrared heaters warm you and objects directly, which works if you sit in one spot, but they heat a closed room less evenly.

Does a bigger heater cost more to run?

No, not if it has a thermostat. Running cost depends on how much heat your room loses, because the heater only has to replace that heat, so a 1,500-watt model that cycles off spends about the same as a smaller one running all the time.

At full power, a 1,500-watt heater uses 1.5 kilowatt-hours per hour, or 12 kWh across an 8-hour night. Multiply that by the rate on your electric bill for the worst case, and expect less if the room is small or the house has other heat.

If what you really want is a warm bed and not a warm room, a heated mattress pad is much cheaper to run. We worked out the numbers in how much electricity a heated mattress pad uses, and the difference is large.

How do you run a bedroom heater safely?

Plug it straight into a wall outlet, keep it 3 feet from anything that can burn, and buy one with automatic tip-over and overheat shutoff. Those three habits prevent most problems.

The U.S. Consumer Product Safety Commission warns against running space heaters on extension cords or power strips, which can overheat under a load this big. In a bedroom, the 3-foot rule includes the bedding, the curtains, and a pile of clothes on the floor.

Check the box or the base for a UL, ETL, or CSA safety listing. The National Fire Protection Association says space heaters cause most home heating fire deaths, and it recommends turning heaters off when you leave the room or go to sleep.

The safest overnight plan is to warm the room before bed and switch the heater off when you lie down. A good comforter, or a weighted blanket you’ve washed and dried the right way, will hold that warmth until morning.

Frequently asked questions

The bottom line on bedroom heater size

Measure the room, multiply by 10, and adjust for high ceilings and drafty windows. For almost every bedroom that points to one 1,500-watt heater with a real thermostat, and spending more won’t get you more heat.

If the room is still cold after that, look at the drafts before you buy a second heater. If you also want to clear the air while the windows stay shut, our picks for quiet air purifiers that fit a small bedroom are worth a look, and the Berry Finds deals hub has the current home and heating deals.