How many watts does a space heater use?
A full-size electric space heater uses about 1,500 watts on high and 750 watts on low, and that high number is nearly universal because a 120-volt cord-and-plug heater is limited to 1,500 watts by safety standards. At 120 volts, 1,500 watts is a 12.5-amp draw, which is most of what a standard household circuit can safely carry. Some models add a middle step around 900 to 1,000 watts, but the pattern holds: two heat levels, with the top one at 1,500 watts.
The type of heater does not change the wattage. A ceramic fan heater, an oil-filled radiator, an infrared quartz heater, and a convection panel set to the same level all pull the same watts and put out the same heat, because they are all electric resistance heaters. What differs is how the heat feels and how it spreads around a room, not how much electricity it uses. Do not pay extra expecting a heater to make more heat per watt, because none of them can.
If you want the exact figure for your unit, read the label. The nameplate on the base or the cord lists the wattage, or the amps; if it gives amps, multiply amps by 120 to get watts. A heater rated 12.5 amps is a 1,500-watt heater. Use that number, not the room-size marketing on the box, whenever you are sizing a circuit, a generator, or an inverter.
How many watts does a space heater use by type and size?
Space heaters fall into three power classes. A personal or under-desk heater draws 200 to 400 watts and warms the air right around you, not a room. A standard portable room heater draws 750 watts on low and 1,500 watts on high, and this covers the vast majority of ceramic, oil-filled, infrared, and convection heaters sold for homes. A 240-volt garage, shop, or utility heater draws 3,000 to 5,000 watts and needs its own 240V circuit, the same class of power as an electric dryer.
Within the standard 1,500-watt class, the differences are about comfort and safety, not consumption. Oil-filled radiators heat slowly and stay warm after they cycle off, so they feel steady and have no exposed hot element. Ceramic fan heaters warm a room fast and move air. Infrared and quartz heaters warm objects and people directly, which feels good in a drafty space but does little once you leave the beam. All of them cost the same to run at the same setting.
For power planning, the only figures that matter are the input watts and the voltage. A 1,500-watt heater on a low 750-watt setting genuinely uses half the power and costs half as much, so the low setting is the easiest saving there is. If you are adding a heater to a backup or off-grid plan, treat it as a 1,500-watt continuous load and run the total through the solar panel calculator with the rest of your appliances.
How much does it cost to run a space heater?
A 1,500-watt space heater costs about $0.26 an hour to run at the 2026 US average residential rate near $0.17 per kWh. The math is simple: 1,500 watts is 1.5 kW, and 1.5 kW for one hour is 1.5 kWh, which at $0.17 is about 26 cents. Run it eight hours a day and that is roughly $2 a day, or about $60 a month. On the low 750-watt setting, halve those numbers. Your actual cost depends on your rate and your runtime, so treat these as estimates.
Run continuously, the bill gets serious. A 1,500-watt heater left on for a full 24 hours uses 36 kWh and costs about $6 a day, close to $180 a month if it truly never shuts off. In practice most heaters have a thermostat that cycles the element on and off to hold a temperature, so the real cost is lower than the 24-hour worst case, often by a third or more in a well-insulated room. A small 400-watt personal heater is far cheaper, about 7 cents an hour, because it heats only you.
The reason a space heater lands high on your bill is duration, not just wattage. A microwave pulls 1,500 watts too, but for two minutes; a space heater pulls it for hours. If the difference between the 1,500-watt draw and the kWh on your bill is fuzzy, our explainer on kW vs kWh sorts it out, and watts to kWh shows the conversion step by step.
Are some space heaters more energy efficient than others?
No. Every plug-in electric space heater is essentially 100 percent efficient at turning electricity into heat, so two heaters set to 1,500 watts produce the same heat and cost exactly the same to run, no matter the brand, the price, or the technology. There is no such thing as a resistance heater that squeezes more warmth out of a watt. Marketing that calls one heater more efficient usually means it has a better thermostat, a timer, or an eco mode that simply runs at lower wattage.
The real savings come from using less power, not from a special heater. A good thermostat that cycles the heater off once the room is warm, a timer, and running on the low setting all cut the bill because they cut the watt-hours. Pointing an infrared heater at the people in the room instead of trying to heat the whole space is the same idea: less runtime at full power.
The one thing that genuinely beats a space heater is a heat pump, which moves heat instead of making it and delivers roughly 2 to 4 units of heat per unit of electricity. That is why heating a whole house with plug-in space heaters is the most expensive way to stay warm. Space heaters win only for zone heating: warming the one room you are in while you turn the central thermostat down, so the heater's cost is more than offset by the furnace or heat pump you are not running everywhere else.
Does a space heater need a dedicated circuit?
A 1,500-watt space heater does not require its own circuit by code, but it should be the only significant thing running on the circuit it is plugged into. At 12.5 amps it uses most of a 15-amp circuit's safe continuous capacity (about 1,440 watts) and a good share of a 20-amp circuit, so plug in a hair dryer, a toaster, or a second heater on the same circuit and the breaker will trip. If your heater keeps tripping the breaker, that is the cause, and it is the system working as intended.
Plug a space heater directly into a wall outlet, never into a power strip or an extension cord. A 1,500-watt load can overheat the thinner wire in a strip or cord and start a fire, and space heaters are already a leading cause of home heating fires. This is a real hazard, not a formality: the heater is fine, but the cord feeding it may not be rated for a sustained 12.5 amps.
A 240-volt garage or shop heater is a different animal. Pulling 3,000 to 5,000 watts, it needs its own dedicated 240V circuit sized to the nameplate, and installing that means working inside the service panel. That is licensed electrician territory and usually a permit, the same as adding a circuit for a dryer or an air conditioner.
Can you run a space heater on solar or a battery?
You can, but a 1,500-watt space heater is one of the worst possible loads for solar and batteries, and for most people the honest answer is do not try. Because a heater is a resistance load, its running watts equal its rated watts with no startup surge, so sizing is simple: you need an inverter or power station rated for at least 1,500 watts of continuous output, and 2,000 watts gives useful headroom. The problem is not the power, it is how long a heater has to run.
Runtime is brutal. A power station with 1 kWh of usable capacity runs a 1,500-watt heater for only about 40 minutes, and a single 100Ah, 12-volt battery (roughly 1 kWh usable in LiFePO4) runs it under an hour. Compare that with the days of phone charging or the full night of running a fridge the same battery gives you, and the reason is the heater's relentless 1,500-watt draw. Our breakdown of what a 100Ah battery can run shows the same math across other appliances.
Solar cannot keep up either. Running a heater eight hours uses about 12 kWh, and a single 100-watt panel makes only 400 to 500 watt-hours on a good day, so you would need on the order of two dozen panels just to feed one space heater. For backup warmth, a small heater on low as a brief boost from a solar generator is fine, but continuous heat should come from fuel or the grid. If you want the sun to help with heat, a solar air heater gives free daytime warmth without touching your battery. Size any real plan with the solar panel calculator before you buy.
Frequently asked questions
Will a 1000 watt generator run a space heater?
Not a full-size one. A standard space heater draws 1,500 watts on high, well past a 1,000-watt generator, so it will overload and shut down. You could run a heater set to its 750-watt low setting, or a small 400-watt personal heater, with a little margin to spare. Check the heater's nameplate wattage against the generator's continuous (running) rating, not its peak surge rating, and remember a resistance heater has no startup surge, so the running watts are what count.
How much would it cost to run a 1500-watt heater for 24 hours in the US?
About $6 a day at the 2026 US average residential rate near $0.17 per kWh. A 1,500-watt heater running a full 24 hours uses 36 kWh, and 36 times $0.17 is roughly $6.12, or close to $180 a month if it truly ran nonstop. In reality the thermostat cycles the element off once the room is warm, so the real cost is usually lower, often by a third in a well-insulated space. Your rate matters most; treat this as an estimate.
What size circuit breaker do I need for a 1500 watt heater?
A 1,500-watt, 120-volt heater draws 12.5 amps and runs fine on a standard 15-amp or 20-amp household circuit, as long as it is the only significant load on that circuit. A 15-amp circuit safely carries about 1,440 watts continuously, so a 1,500-watt heater sits right at the edge and will trip the breaker if anything else shares the line. A 240-volt garage heater pulling 3,000 to 5,000 watts needs its own dedicated 240V circuit sized to the nameplate, installed by an electrician.
Does a 400 watt heater use a lot of electricity?
No, relatively little. A 400-watt personal heater uses 0.4 kWh per hour, about 7 cents at average US rates, roughly a quarter of what a 1,500-watt heater costs. It draws about 3.3 amps, so it can share a circuit without tripping a breaker. The tradeoff is that a 400-watt heater warms only the space right around you, not a room, so it works as a spot heater at a desk but will not take the chill off a whole living room.
How long will a solar power station run a space heater?
Not long. A power station with about 1 kWh of usable battery runs a 1,500-watt heater for roughly 40 minutes, and even a large 3 kWh unit lasts only about two hours. Space heaters are the fastest way to drain any battery because they pull 1,500 watts continuously with no let-up. Confirm the station's continuous AC output clears 1,500 watts (many 1 kWh units cap at 1,000), and plan on solar for brief backup warmth only, not all-day heating.