The first hot week of summer is when most people discover that comfort has a price tag. A window air conditioner usually costs less to run than a central system because it cools one room, but the bill still depends a lot on the unit’s size and your electricity rate.
Short answer: about 8 to 36 cents an hour while the compressor is running, depending on size and your rate. At 8 hours a day, that is roughly $12 to $56 a month once you allow for the compressor cycling off.
The one formula worth knowing
Watts are roughly the BTU rating divided by the EER, the efficiency number on the unit’s label. Many window units sit around 10 to 12 EER. A 5,000 BTU unit at EER 10 draws about 500 watts. Then cost per hour is watts divided by 1,000, times your rate. We use 16 and 30 cents per kWh.
| Size | Typical watts (EER 10) | Per hour at 16¢ | Per hour at 30¢ |
|---|---|---|---|
| 5,000 BTU | about 500 W | 8.0¢ | 15.0¢ |
| 8,000 BTU | about 800 W | 12.8¢ | 24.0¢ |
| 12,000 BTU | about 1,200 W | 19.2¢ | 36.0¢ |
What it costs per month
An air conditioner does not run flat out all day. When the room reaches the set temperature, the compressor cycles off and only the fan keeps going. One source notes a 1,000 watt unit can average closer to 650 watts over an hour. The table below uses about 65 percent of the rated draw, 8 hours a day, for 30 days.
| Size | Per month at 16¢ | Per month at 30¢ |
|---|---|---|
| 5,000 BTU | about $12 | about $23 |
| 8,000 BTU | about $20 | about $37 |
| 12,000 BTU | about $30 | about $56 |
In a heat wave, with the unit working hard all day, the compressor runs more and the bill climbs. The worst case, a 12,000 BTU unit at full power for 8 hours a day, is about $46 at 16¢ and $86 at 30¢ a month.
What changes the bill the most
- Your electricity rate. The same unit costs almost twice as much at 30¢ as at 16¢.
- Whether the unit fits the room. An undersized unit runs constantly. An oversized one cools quickly, shuts off and leaves the air clammy. Our BTU sizing chart and AC BTU calculator help you pick.
- Sun and air leaks. A sunny window and a gap around the unit make it work harder all day.
- Efficiency. A higher EER means fewer watts for the same cooling.
- Hours of use. Running it only when you are home and in the room is the biggest lever of all.
Six ways to cut the cost
- Close blinds or curtains on sunny windows before the day heats up.
- Seal gaps around the unit with foam strips or the accordion panels that come in the box.
- Set the thermostat a little higher when you are home. Energy.gov suggests about 78°F.
- Use the energy-saver or eco mode so the fan stops when the compressor does.
- Clean the filter every couple of weeks during the season so air flows freely.
- Add a fan to spread the cool air so you can set the AC a bit higher.
Not sure a window unit is the right type? Compare the running costs in portable vs window vs mini split air conditioners, or check out common AC sizing mistakes. To compare with other appliances, use the running cost calculator or browse our climate and energy guide.
