Here is the entire cost story in one line: a typical space heater on high draws about 1500 watts, which is 1.5 kilowatt-hours of electricity for every hour it runs. Your bill charges you per kilowatt-hour, so the cost to run it is simply 1.5 × (hours you run it) × (your electricity rate). That's it. Plug in your own rate from your bill and you have the real number — no guessing, no fabricated averages.
Why "100% efficient" still costs a fortune
People hear that resistance heaters are "100% efficient" and assume that means cheap. It doesn't. 100% efficient just means all the electricity becomes heat — none is wasted. But electricity is an expensive way to buy heat compared to natural gas, and there's a device that beats resistance heating outright: a heat pump doesn't make heat, it moves heat from outside to inside, and it can deliver two to four units of heat for every unit of electricity it uses. A resistance heater is locked at one-for-one. So "100% efficient" is the ceiling for resistance heat and the floor for a heat pump.
The "all 1500W heaters are equal" reality
This is worth saying plainly because it kills a lot of marketing: any two heaters drawing the same watts put out the same amount of heat and cost the same to run. Ceramic, infrared, oil-filled, "energy-saving" — at the same wattage, the heat and the cost are identical. What differs is how the heat is delivered (fast air vs. radiant vs. slow gentle warmth), not how much you get per dollar. Don't pay extra for a heater that promises to break the watt math; it can't. (We dug into this in all 1500-watt heaters put out the same heat.)
The one place a space heater actually saves money
Zone heating. If you turn your whole-house thermostat down and use a space heater to warm only the one room you're actually in, you can come out ahead — because you've stopped paying to heat the empty rooms. The space heater only saves money when it replaces central heating in unused space, never when it runs on top of a normal thermostat setting. Heat the person and the room, let the rest of the house go cool, and the math can tip in your favor.
| Run time (at 1500 W) | Energy used | Your cost |
|---|---|---|
| 1 hour | 1.5 kWh | 1.5 × your rate |
| 8 hours/day | 12 kWh/day | 12 × your rate, daily |
| 8 hours/day for a month | ~360 kWh | 360 × your rate |
Fill in your own per-kWh rate from your utility bill — that's the only number that makes this real, and it's the one no article can honestly supply for you.
One safety number worth knowing
1500 watts at a standard 120-volt outlet is about 12.5 amps — close to the limit of a typical household circuit. That's why the instructions say plug a space heater directly into the wall, never into a power strip or a light-duty extension cord: those aren't built for a continuous 12.5-amp draw and are a real fire risk. The cheapest way to run a heater badly is to plug it in wrong.
The short version
A space heater costs 1.5 kWh per hour on high, times your rate — do that one calculation and budget honestly. Don't expect any brand or heating "technology" to beat the watt math; they all obey it. And use it the one way that saves money: turn the house thermostat down and heat only the room you're in. For choosing the heater itself, see our space heater buying guide.
Space heaters and zone-heating gear on eBay
A right-sized heater for the room, plus the smart plug and thermostat that make zone heating actually save money. We earn a small commission on qualifying sales and pass a share to the charity you choose; your price is unchanged. Full disclosure.