How much does a window air conditioner, 12,000 BTU cost to run?
About 20p an hour in the UK and 14¢ an hour in the US. A window air conditioner, 12,000 BTU draws about 1,100 W for roughly 70% of the time it is switched on, so it averages 770 W. Needs a 2,400 W-class inverter and empties most stations inside two hours.
What it costs, by how long it runs
| Running for | kWh | UK | US |
|---|---|---|---|
| 10 minutes | 0.13 | 3.4p | 2.4¢ |
| An hour | 0.77 | 20p | 14¢ |
| An 8-hour night | 6.16 | £1.62 | $1.13 |
| A full day (24 hours) | 18.48 | £4.86 | $3.39 |
| A month at 8 hours a day | 184.8 | £48.64 | $33.89 |
UK prices use the Ofgem price cap for 1 October to 31 December 2026 (direct debit, average across England, Scotland and Wales, with no VAT on electricity this winter): 26.32p per kWh (Ofgem). The standing charge of 54.83p a day is paid whatever you run, so it is left out. US prices use the US average residential price for June 2026 from the Energy Information Administration: 18.34¢ per kWh (EIA). Your own tariff is on your bill; scale the figures by it.
Measure your own
These are typical figures for a typical unit. A plug-in energy monitor between the socket and the appliance shows the real watts and adds up the kWh, so after a day or a week you know exactly what it costs on your tariff.
Compared with similar appliances
| Appliance | Average W | UK per hour | US per hour |
|---|---|---|---|
| Mini fridge | 21 | 0.55p | 0.45¢ |
| Desk fan | 25 | 0.66p | 0.46¢ |
| Under-counter fridge | 26 | 0.67p | 0.55¢ |
| Bait freezer (small chest) | 34 | 0.89p | 0.62¢ |
| Chest freezer | 40 | 1.1p | 0.88¢ |
| Fridge-freezer (full size) | 42 | 1.1p | 0.96¢ |
| Pedestal fan | 50 | 1.3p | 0.92¢ |
| Ceiling fan | 60 | 1.6p | 1.1¢ |
| Box fan | 75 | 2p | 1.4¢ |
| Window air conditioner, 5,000 BTU | 350 | 9.2p | 6.4¢ |
| Window air conditioner, 8,000 BTU | 490 | 13p | 9¢ |
| Portable air conditioner, 8,000 BTU | 630 | 17p | 12¢ |
| Window air conditioner, 12,000 BTU | 770 | 20p | 14¢ |
Running it in a power cut
See which power station will run a window air conditioner, 12,000 BTU, and for how long.
Appliance draw modelled on web.archive.org. The US Department of Energy retired this page in 2025; the link is the Internet Archive's June 2024 capture. The figures remain typical ranges for a typical unit, not a specification.
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