“Space heaters are expensive to run” is one of those things everyone repeats and almost nobody checks. The truth is simpler and more useful: a heater’s running cost is just its wattage multiplied by your electricity rate, and the difference between a big heater and a small one is bigger than most people expect. Here is the math, with real numbers.
The quick answer
Watts ÷ 1,000 × hours × your rate per kWh = cost. A 1,500 W heater at 16¢/kWh costs about 24¢ an hour; a 500 W heater costs about 8¢ an hour — and only 5¢ at 10¢/kWh. A thermostat and timer cut the real figure further, because the heater cycles instead of running flat out.
Step 1: find the wattage
It is printed on the label, in the manual or on the product page. Most plug-in and desk-size heaters are 350–750 W; most floor-standing space heaters are 1,500 W, because that is the most a standard US outlet circuit comfortably delivers. The number matters more than anything else in this article.
Step 2: find your electricity rate
Look at your bill for the price per kilowatt-hour (kWh). The US residential average is in the mid-teens of cents per kWh, but it ranges from under 10¢ in some states to over 30¢ in others. Use your real number.
Step 3: do the math
- Convert watts to kilowattsDivide by 1,000. A 1,500 W heater is 1.5 kW; a 500 W heater is 0.5 kW.
- Multiply by hoursRunning 8 hours a night: 1.5 kW × 8 = 12 kWh; 0.5 kW × 8 = 4 kWh.
- Multiply by your rateAt 16¢/kWh: 12 kWh = $1.92 a night; 4 kWh = $0.64 a night.
500 W vs. 1,500 W: a month of evenings
| Heater | Per hour | 8 h per night | 30 nights |
|---|---|---|---|
| 1,500 W floor heater | 24¢ | $1.92 | $57.60 |
| 500 W plug-in heater | 8¢ | $0.64 | $19.20 |
| 500 W at 10¢/kWh | 5¢ | $0.40 | $12.00 |
Full-power figures at 16¢/kWh unless noted. Real use with a thermostat is lower.
The thermostat effect (why real bills are lower)
The table assumes the heater runs at full power the whole time. It doesn’t. A heater with a thermostat heats the room up, then switches the element off and on to hold the temperature you set. In a reasonably insulated room, that can mean the element is actually running well under half the time. A timer does the rest: the heater switches itself off an hour after you fall asleep instead of running until morning.
Space heater vs. turning up the thermostat
This is where small heaters earn their keep. Central heating warms every room — the empty guest room, the hallway, the kitchen at 2 a.m. — whether anyone is in it or not. The classic money-saving move is the opposite: lower the central thermostat a few degrees, and heat only the room you’re actually using with a small heater on its own thermostat. For a home office or a bedroom, a 500 W unit on a timer is a rounding error on the bill.
How to keep the cost down
- Size the heater to the room. A 500 W unit for a bedroom or office; save the 1,500 W box for a large, cold space.
- Use the thermostat. Set a target temperature instead of running on “high”.
- Use the timer. Especially at night — warm the room while you fall asleep, then let it switch off.
- Close the door. You are heating one room; don’t let it leak into the hallway.
- Point it at people, not walls. An oscillating airflow that reaches the floor warms you faster at the same wattage.
The heater we use for one room
The numbers above are why we like the Ultra Air Heater for the one-cold-room problem. It is a 500 W ceramic heater that plugs straight into the wall outlet — the maker puts the running cost at about 5 cents an hour at 10¢/kWh — with an LCD thermostat, a timer and a remote control, so it does exactly the cycling and switching off described above without you thinking about it. The maker rates it for rooms up to 350 sq ft, and it has automatic overheat and tip-over shut-off. One owner, Joseph D., summed it up on the official site: “We get to enjoy the warmth and comfort, but our electricity bill was less.”
Frequently asked questions
How much does it cost to run a 1,500 W space heater for 8 hours?
At the US average of about 16¢ per kWh: 1.5 kW × 8 hours = 12 kWh, which is about $1.92 per night, or roughly $58 a month if you do it every night. A thermostat that cycles the heater on and off typically cuts that number noticeably.
How much does a 500 W heater cost to run?
Half a kilowatt-hour per hour. At 10¢/kWh that is 5¢ an hour; at 16¢/kWh it is 8¢ an hour. Eight hours a night for a month comes to roughly $12–$19 at full power, and less with a thermostat.
Is it cheaper to use a space heater or central heating?
For one room, a small space heater on a thermostat is usually cheaper, because central heating warms every room in the house whether anyone is in it or not. For the whole house, central heating normally wins. The trick is to lower the thermostat a few degrees and heat only the room you are using.