In the UK, running an air conditioner usually costs between 10p and 40p per hour. The exact cost depends on the unit, room, weather and electricity rate.
An efficient bedroom split usually sits near the lower end. A portable unit cooling a sunny living room may cost more.
Air conditioning running-cost examples
These examples use an electricity price of 26p per kWh. They show possible average electricity use while cooling, but actual figures vary by model and room.
| Example | Average electricity use | Cost per hour | Eight hours | Eight hours a day for 30 days |
|---|---|---|---|---|
| Small efficient split system | 0.4 kW | 10p | £0.83 | £25 |
| Bedroom or small-room system | 0.7 kW | 18p | £1.46 | £44 |
| Larger split or medium living room | 1.0 kW | 26p | £2.08 | £62 |
| Portable unit working hard | 1.2 kW | 31p | £2.50 | £75 |
The figures exclude the standing charge, which you pay whether the unit runs or not.
What is the UK electricity price to use?
Ofgem’s average capped electricity rate for a standard variable tariff paid by Direct Debit is 26.11p per kWh from July to September 2026. It goes up to 26.32p per kWh from October to December 2026.
This guide uses 26p per kWh. Check your bill because your rate may differ.
Ofgem covers England, Scotland and Wales. Northern Ireland has a separate electricity market, and households can compare supplier prices through the Consumer Council.
You can check the latest Great Britain figures on Ofgem’s energy price cap unit rates and standing charges page.
What would be your running cost?
You need three numbers:
- The air conditioner’s electricity use in kW
- The number of hours it runs
- Your electricity price per kWh
Use this calculation:
Electricity use × hours × electricity price = running cost
For example, a unit averaging 0.7 kW for eight hours at 26p per kWh would cost:
0.7 × 8 × £0.26 = £1.46
Over 30 nights, that adds up to about £43.70.
Cooling capacity is not electricity use
This is where air conditioning costs can get confusing.
A 3.5 kW or 12,000 BTU/h air conditioner has around 3.5 kW of cooling capacity. It does not normally consume 3.5 kW of electricity.
Look at the technical sheet or energy label to find the electrical input or rated power. A higher SEER usually means the unit is more efficient over the cooling season.
An inverter may use more power to cool a hot room, then reduce its output. Multiplying the maximum input by every hour can overestimate the cost.
How much does air conditioning cost overnight?
At 26p per kWh, a unit averaging 0.4 kW would cost about 83p for eight hours. A unit averaging 0.7 kW would cost about £1.46.
Once the bedroom is cool, an inverter unit may only need to keep the temperature steady. Cooler air outside at night can also help reduce how hard the unit has to work.
A loft room with poor insulation can stay hot even after sunset. Leaving doors and windows open also makes the air conditioner work harder.
For a bedroom-specific example, see our night-time air-conditioning guide.
What could air conditioning cost during a heatwave?
Suppose a living room system averages 1 kW and runs for eight hours a day. At 26p per kWh, it costs about £2.08 per day.
In a seven-day hot spell, that is about £14.56. The same schedule over 30 hot days would cost around £62.40.
Hot, sunny weather can increase electricity use, while milder weather can lower it.
Portable versus split-system costs
Portable air conditioners are popular and easy to set up, but they are often less efficient in practice.
The exhaust hose lets out heat, and any gaps around the window kit can let warm air back in. This can make the unit run at high power for longer periods.
A split system moves heat outside. Inverter models can lower their output once they reach the set temperature, which often makes them quieter and cheaper to run for the same amount of cooling.
Do not just compare two systems by their BTU/h rating. Also look at how much electricity they use and how efficient they are.
Our portable-versus-split comparison looks at running costs and upfront trade-offs in more detail.
What changes the running cost?
Outdoor temperature
The hotter it is outside, the harder the system has to work. Costs will rise during the hottest part of a heatwave.
Thermostat setting
Setting your air conditioner to 20°C usually uses more energy than setting it to 24°C or 25°C. Try to choose a comfortable temperature instead of making the room very cold.
Room size and system size
A large or open-plan area needs more cooling than a small bedroom. If the unit is too small, it may run all the time without making the room comfortable.
Insulation, sunlight and windows
Poor insulation, big windows and direct sunlight can make a room hotter. Close blinds or curtains before the room heats up, and keep windows shut while using the air conditioner.
Number of units
Running two air conditioners at the same time will cost more than running just one. However, cooling only the rooms you use may be cheaper than trying to cool your whole home from a single central unit.
How do you lower your air conditioning costs?
- Choose the right capacity for the room.
- Use a sensible temperature setting.
- Shade sunny windows before the room heats up.
- Keep doors and windows closed while cooling.
- Clean the filters as the manufacturer recommends.
- Cool only the rooms you use.
- Compare SEER ratings when selecting a new system.
Try not to turn the system on and off every few minutes. An inverter unit will usually lower its output once the room reaches the temperature you set.
Estimate your own air conditioning costs
Generic examples cannot account for your rooms, equipment, schedule or electricity rate.
CostToCool gives you two free ways to estimate your running costs:
- Calculate my current setup if you already have air conditioning. Add each unit, cooled area, schedule and electricity price to see estimated costs per week, 30 days and cooling season.
- Plan cooling for my home if you have not bought a system yet. Add your rooms and conditions to see the recommended cooling capacity and estimated running costs.
Both tools are free. The results are estimates, but they are more useful than a single national average.