Cost to run a window air conditioner
A window air conditioner drawing 666.7 W costs 17.5p for each hour of running at 26.32p/kWh. Used 6 hours a day, 4 days a week, that comes to £18.30 a month.
An hour of running costs
17.5p an hour
That is 0.67 kWh. Used as set, it comes to £18.30 a month and £219.59 a year.
On the label or in the manual.
Standby, thermostats and off-peak use
A thermostat switches it on and off to hold a temperature. 100% if it runs flat out.
Drawn while plugged in and not running.
| Period | Cost | Energy | CO2e |
|---|---|---|---|
| An hour of running | 17.5p | 0.67 kWh | 145 g |
| A day, on average | 60.2p | 2.29 kWh | 497 g |
| A month | £18.30 | 69.5 kWh | 15.1 kg |
| A year | £219.59 | 834 kWh | 181 kg |
How we calculated this
Energy is power multiplied by time: 666.7 W running for an hour uses 0.67 kWh.
The figures are for ENERGY STAR certified models sold in the US and Canada. Certified models are more efficient than the average model on sale, and many are larger than the ones sold in Europe, so an older or less efficient one will use more. The power is ENERGY STAR’s annual figure divided by the 750 hours of compressor operation it assumes, so it is what the unit draws while its compressor runs. The median certified unit cools 10,000 Btu an hour, and a bigger one draws more. It cycles on and off, so it draws this for only part of the hours it is switched on.
The starting use for a window air conditioner, 6 hours a day, 4 days a week, is where the calculator starts, not a measurement of your home: change it to how you use yours. A day is the average across the week, and a month is a twelfth of a 365-day year.
Electricity costs 26.32p/kWh. That is the published figure for the United Kingdom, 1 Oct – 31 Dec 2026, from Ofgem. Average for England, Scotland and Wales, paying by Direct Debit. No VAT on electricity from 1 October 2026 to 31 March 2027.
Standing charges are left out: you pay them whether or not the appliance runs.
Emissions use 0.217 kg CO2e per kWh, the lifecycle intensity of electricity generated in the United Kingdom in 2025, from Ember, via Our World in Data. Lifecycle means building the power stations and supplying their fuel are counted too. It is the grid’s average, not the particular power station an extra appliance brings on.
What drives the cost
A window air conditioner moves heat out of the room, and it draws 666.7 W while its compressor runs, which is many times a fan. It runs only part of the hours it is on, so the hours you set here are the hours the compressor is working; at 6 hours a day, 4 days a week it costs £219.59 a year at 26.32p/kWh.
Also called: room air conditioner, wall air conditioner, AC unit, window AC.
What it costs in the UK, Europe and the US
For a window air conditioner used as typical (6 hours a day, 4 days a week), at each country’s published average electricity price.
| Country | Electricity price | An hour |
|---|---|---|
| United Kingdom | 26.32p/kWh | 17.5p |
| United States (average) | 18.19¢/kWh | 12.1¢ |
| Ireland | €0.4042/kWh | €0.27 |
| Germany | 0,3869 €/kWh | 0,26 € |
| France | 0,2561 €/kWh | 0,17 € |
| Spain | 0,2669 €/kWh | 0,18 € |
| Italy | 0,2966 €/kWh | 0,20 € |
| Netherlands | € 0,2558/kWh | € 0,17 |
Compared with similar appliances
| Appliance | Typical power | An hour | A year, typical use |
|---|---|---|---|
| Window air conditioner | 666.7 W | 17.5p | £219.59 |
| Ceiling fan | 17.3 W | 0.46p | £7.09 |
| Window fan | 152.5 W | 4.01p | £66.97 |
| Dehumidifier | 500 W | 13.2p | £288.20 |
How to spend less on it
- Close the windows and curtains on the sunny side and keep doors shut: the less heat that comes in, the less the compressor has to remove.
- Set the thermostat higher than you think you need: every degree warmer is less running time.
- Use a fan alongside it so a higher setting still feels cool, and switch it off when you leave the room.
- Clean the filter: a clogged one makes it work harder for less cooling.
Questions
How much does a window air conditioner cost to run per hour?
At 26.32p/kWh, a window air conditioner drawing 666.7 W costs 17.5p for every hour of running at full power.
How much does a window air conditioner cost to run a year?
Used 6 hours a day, 4 days a week, it costs about £219.59 a year at 26.32p/kWh, or £18.30 a month.
How many watts does a window air conditioner use?
Most draw between 500 W and 1,222 W while running, and 666.7 W is typical. The rating is on the label or in the manual.
How much does a window air conditioner cost to run?
While its compressor runs a typical certified unit drawing 666.7 W costs 17.5p an hour at 26.32p/kWh. Across 462 models most draw between 500 W and 1,220 W, and a bigger or older one draws more.
Does it run all the time it is switched on?
No: the compressor switches on and off to hold the temperature, so it runs for only part of the time. A hotter day, a bigger room or a sunnier window means more of the time.
Sources
- ENERGY STAR Certified Room Air Conditioners (open data), ENERGY STAR, US Environmental Protection Agency, 26 September 2026. “ENERGY STAR certified window air conditioners, power while the compressor runs: median 667 W across 462 certified models, 10th to 90th percentile 500 W to 1,220 W (models where type='Window').”
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