Quick answer: Space heater watts are exactly what the label says: 750 W or 1,500 W, drawing 6.25 A or 12.5 A at 120 V. At the June 2026 US average that is 13.8 or 27.5 cents an hour. Neither setting is more efficient than the other, because every electric heater turns essentially all its electricity into heat.
Of all the loads in our appliance wattage chart, this is the one you can trust the label on. A resistance heater has no motor, no compressor and no power factor, so volts times amps really is watts here. The 1,500 on the box is the 1,500 you get.
Which makes it the most honest appliance in the house, and also the most expensive thing you can plug into an ordinary socket.
Space heater watts and what each setting costs
| Setting | Amps at 120 V | Per hour US | Per hour UK | An 8-hour night | A month of nights |
|---|---|---|---|---|---|
| 1,500 W | 12.50 | 27.5¢ | 39.2p | $2.20 | $66.02 / £94.00 |
| 750 W | 6.25 | 13.8¢ | 19.6p | $1.10 | $33.01 / £47.00 |
Put that next to everything else this site has measured and the scale becomes obvious. A 1,500 W heater costs more per hour to run than a 1 HP submersible well pump, and about sixty times what a typical certified chest freezer averages. It is the largest continuous load you can plug into an ordinary socket: anything hungrier, like an electric water heater or a dryer, needs its own higher-rated circuit.
The efficiency question has a boring answer
Shopping for a space heater means wading through claims about efficiency, and almost all of them are meaningless. Every electric resistance heater converts essentially all of its electricity into heat in your room. There is nowhere else for the energy to go.
So a $25 heater and a $250 heater set to the same wattage produce the same heat and cost the same to run. What the expensive one may genuinely buy you is a better thermostat, quieter operation, oscillation, a tip-over switch, or a shape that puts the heat where you are. None of that is efficiency. Nothing can be more than 100 percent efficient, and a resistance heater is already there.
The one real exception is a heat pump, which moves heat rather than making it and can deliver several units of heat per unit of electricity. That is a different machine at a different price, not a space heater.
So which setting should you use?
This is where people expect a trick and there is not one, but the answer does depend on how your heater is controlled.
- With a thermostat, the setting barely matters for cost. The heater runs until the room reaches temperature, then cycles. Energy used over the evening is set by how fast your room loses heat, not by which element is switched on. High gets there faster; low gets there slowly and then keeps up, if it can keep up at all.
- Without a thermostat, low costs exactly half. It also delivers exactly half the heat. If half is enough for the room, use it. If it is not, you will sit there cold having saved nothing, because the room never reaches the temperature you wanted.
- Low is the safer choice on a shared circuit. At 750 W the heater takes 6.25 A instead of 12.5, which is the difference between using up most of a circuit and using up less than half of it.
That circuit point deserves its own sentence. A 1,500 W heater draws 12.5 A of a 15 A circuit, leaving 2.5 A, about 300 W, for everything else sharing it. Two of them on the same circuit come to 25 A and the breaker will say no. This is why heater manuals tell you to plug it straight into a wall outlet.
On backup power, space heater watts ruin everything
Here is the number that matters if you are reading this during an outage. A 1,500 W heater empties a 1 kWh portable power station in about 40 minutes, before inverter losses. Even a large 3.6 kWh unit gives you under two and a half hours.
Compare that with the alternative most houses already have. If your heating is gas, the only thing missing during an outage is the electricity to run the fan, and that fan draws 90 W on its lowest setting. The same battery that gives you 40 minutes of one warm room gives you around eleven hours of the whole house, because the heat itself is still coming from gas.
A generator changes the arithmetic but not the conclusion: it has to produce all 1,500 W, burning considerably more than that in fuel to do it, for heat you could have had by running a 90 W fan. Electric heat and backup power are a bad combination, and knowing that before you buy either one is the whole point of sizing properly.
Safety. This is not a routine warning. US Fire Administration figures for 2017 to 2019 show portable heaters caused an average of 1,100 residential fires and 65 deaths a year. They were only 3 percent of heating fires but 41 percent of the fatal ones, and a quarter of them happened in January.
The leading cause is not a faulty heater. It is the heat source being too close to something that burns, at 47.9 percent of cases. Unattended equipment accounts for another 10 percent. A third of these fires start in bedrooms, and bedding is the most common thing to catch.
Keep three feet, about a metre, clear on every side, never run it while asleep or out, plug it directly into a wall outlet rather than an extension lead or power strip, and check you have a working smoke alarm: one was present in only 41 percent of these fires. If you are running a generator during an outage it goes outside, well away from openings, because carbon monoxide kills faster than cold does.
Frequently asked questions
How much does a 1500W heater cost to run per hour?
27.5 US cents at the June 2026 average of 18.34 cents per kWh, or 39.2 pence at the Ofgem capped rate. Eight hours is $2.20, and a month of eight-hour nights is about $66.
Does the 750W setting save money?
Per hour of running, exactly half. Over an evening with a thermostat, hardly anything, because the heater simply runs longer to reach the same temperature. The energy your room needs is set by how fast it loses heat, not by the switch.
Are expensive space heaters more efficient?
No. All electric resistance heaters turn essentially all their electricity into heat, so at the same wattage they cost the same to run. Price buys controls, safety features and how the heat is distributed, not efficiency.
Can I run a space heater on a power station or generator?
Briefly. A 1,500 W heater drains a 1 kWh battery in about 40 minutes. If you have gas heating, powering the furnace blower instead gives you roughly seventeen times the hours and warms the whole house.
Why does my heater trip the breaker?
Because at 1,500 W it is drawing 12.5 A of a 15 A circuit and something else on that circuit is taking the rest. Two heaters on one circuit is 25 A and will always trip. Move it to its own outlet, and never onto an extension lead.
This article is general information, not an installation guide and not a substitute for a licensed electrician. Electrical work on a service panel, a transfer switch or a utility connection is regulated in most jurisdictions and normally requires a permit and an inspection. Fuel-burning equipment produces carbon monoxide and must never be run indoors, in a garage or near an opening into the home.
