At the Ofgem cap rate for 1 July to 30 September 2026, a portable air conditioner rated 1500W costs about £1.37 a use and £41.12 a year when 5 hours a time, once a day.
| Per hour of running | 27.4p |
|---|---|
| Per use | £1.37 |
| Per day | £1.37 |
| Per year | £41.12 (157 kWh, over 30 days of use) |
Calculated at 26.11p per kWh, the capped electricity unit rate for 1 July to 30 September 2026 on a standard variable tariff paid by direct debit, including VAT. The 57.19p daily standing charge is not included, because you pay that whether or not anything is switched on.
Two things worth knowing about that figure. The cap limits the unit rate, not your bill, so using more still costs more. And it is a Great Britain average: the actual capped rate is set per region, running from roughly 25.1p in the East Midlands to 27.7p in North Wales and Mersey, so your own rate could move these numbers by around a tenth either way. It is on your bill.
The annual figure assumes 30 days of use a year rather than 365, because air conditioner is seasonal. Running it every day of the year would cost £500.33.
Air conditioner has a thermostat, so the element or compressor switches off once it reaches temperature and back on when it drifts. The figures above assume it draws full power roughly 70% of the time it is on, which is typical.
This is where most running-cost figures online go wrong. Multiplying 1500W by the hours it is switched on would give £714.76 a year, which is roughly 1.4 times the real figure.
Figures for air conditioner run from about 700W to 3000W. Cooling output is quoted in BTU and the electrical draw is a separate figure, so a unit advertised as 12,000 BTU might draw 1.2kW. Portable units vent hot air through a hose, and any gap around that hose pulls warm air back into the room, which makes the unit run longer for the same result.
Seal the window around the exhaust hose properly, keep the hose short and straight, and close curtains on the sunny side during the day. Cooling one room with the door shut costs far less than trying to cool a whole floor.
Comparing units on BTU alone. Two units with the same cooling output can differ substantially in what they draw.
Annual running cost against the appliances closest to it, on the same assumptions. The ordering surprises people: short bursts of very high wattage usually cost less than something modest left on for hours.
| Appliance | Per year |
|---|---|
| Laptop | £45.74 |
| Games console | £42.89 |
| Air conditioner | £41.12 |
| Television | £38.12 |
| Hair dryer | £23.83 |
Across a year, a portable air conditioner on these assumptions is about 6.3% of a typical annual electricity bill of £652.75 at these rates.
The figures here use the capped rate. If you are on a fixed tariff, or you want to add several appliances together, put your own unit rate into the energy cost calculator on the homepage.