How much does an air conditioner cost to run in the UK?
Sources and calculations reviewed 28 August 2026. How we review our guidance
At the July–September 2026 Ofgem average rate of 26.11p per kWh, an air conditioner drawing 1 kW costs about 26p per hour at full input. Six hours costs about £1.57. Your actual figure depends on the electrical input shown on the unit, your tariff and how often its compressor cycles.
Use the air conditioner running cost calculator for your own wattage, schedule and electricity rate.
The calculation
The dependable formula is:
Input power (kW) × hours used × electricity rate (£/kWh) = cost
Use electrical input power, normally printed in watts on the rating plate or specification sheet. Do not substitute cooling capacity: a unit described as 2.6 kW cooling does not continuously draw 2.6 kW from the socket.
For example, a 1,200 W unit is 1.2 kW. If it runs at that input for six hours:
- Energy: 1.2 kW × 6 hours = 7.2 kWh
- Cost: 7.2 kWh × £0.2611 = about £1.88
Cost per hour, day and month
The table uses 26.11p/kWh and assumes the unit draws its rated input throughout. “Month” means six hours a day for 30 days.
| Input power | Per hour | Six-hour day | 30 days at 6 hours/day |
|---|---|---|---|
| 500 W | £0.13 | £0.78 | £23.50 |
| 800 W | £0.21 | £1.25 | £37.60 |
| 1,000 W | £0.26 | £1.57 | £47.00 |
| 1,200 W | £0.31 | £1.88 | £56.40 |
| 1,500 W | £0.39 | £2.35 | £70.50 |
These are not forecasts of a whole-home bill. Your tariff may differ, and a thermostat-controlled compressor may switch off while the fan continues running.
A 9,000 BTU worked example
If input watts are unavailable, input power can be estimated from cooling capacity and EER.
A 9,000 BTU/h unit provides roughly 2.64 kW of cooling. At an EER of 2.5, estimated electrical input is:
2.64 kW cooling ÷ 2.5 EER = about 1.06 kW input
At 26.11p/kWh that is approximately:
- 28p per hour at rated input
- £2.20 for eight hours
- £198 for eight hours a day across 90 days
Real consumption can be lower if the compressor cycles. It can stay close to rated input when the room gains heat quickly, the exhaust window is poorly sealed or the unit is undersized.
What changes the real running cost?
Room and unit size
An undersized unit may run continuously without reaching the target temperature. An excessively large unit can cycle abruptly and remove humidity poorly. Start with the BTU calculator and then compare input wattage between suitably sized models.
Window and hose setup
A portable unit must reject heat outdoors. Gaps around an open window let warm air back in, while a long, crushed or hot exhaust hose adds heat to the room. Our window-kit and venting guide explains how to reduce those losses.
Thermostat setting and weather
Trying to hold 18°C during a heatwave requires more compressor time than aiming for a comfortable, moderate reduction. Close blinds before direct sun reaches the glass and cool the occupied room rather than open circulation spaces.
Efficiency
EER compares cooling output with input power at a stated condition. A higher EER means more cooling for each unit of electricity, provided the figures are measured on a comparable basis. Use the efficiency comparison calculator to compare two candidates.
Portable versus split-system costs
Split systems normally place the compressor outdoors and avoid the negative pressure created by many single-hose portable units. They are generally quieter and more efficient in regular use. Portables avoid installation cost and make sense for occasional cooling, renters and rooms where permanent work is unsuitable.
Compare total ownership rather than the electricity bill alone: purchase price, installation, maintenance, expected usage and how many rooms you need to cool all matter.
How to reduce air-conditioning costs
- Check the unit’s input watts before buying.
- Match capacity to the room instead of buying by price alone.
- Seal the exhaust opening and keep the hose short and straight.
- Close doors to unoccupied rooms.
- Shade sunny windows before the room heats up.
- Clean filters at the interval stated in the manual.
- Use a timer rather than leaving the unit on unattended.
- Enter your actual tariff into the calculator instead of relying on a national average.
The Ofgem price cap is an average for a typical payment method, not a universal tariff. Always use the unit rate from your own energy bill when budgeting.