How much does air conditioning cost to run in the UK?
The honest headline: less than most people fear, if you buy the right type. A modern inverter split system cooling a bedroom typically costs 15–30p per hour; a portable unit doing a worse job of the same room costs 25–35p per hour. Run a split for six hours on each of the 30 hottest evenings of the year and you've spent roughly £30–£55 — the price of one takeaway per summer for sleeping through heatwaves.
Work out your exact cost
Estimated running cost
Estimates assume typical real-world efficiency: inverter splits average roughly a third of rated capacity in electrical draw once the room is at temperature (SEER ~6+); portables run closer to 40% of rated capacity (lower efficiency, heat leaking back in). Actual use varies with room, weather and thermostat setting.
Typical costs at a glance
| System | Power draw (typical) | Cost per hour* | 6 hrs/day for a month |
|---|---|---|---|
| 2.5 kW inverter split (bedroom) | 0.5–0.9 kW | 13–23p | £23–£42 |
| 3.5 kW inverter split (living room) | 0.7–1.2 kW | 18–31p | £33–£56 |
| 9,000 BTU portable | 1.0–1.3 kW | 26–34p | £47–£61 |
| Multi-split, two rooms running | 1.5–2.5 kW | 39–65p | £70–£117 |
*At 26p/kWh. Inverter systems draw far less once the room reaches temperature — the ranges reflect hot-day averages, not startup peaks.
Why splits cost less to run than portables
It comes down to where the machinery lives and how it's controlled. A split system's compressor sits outside, rejecting heat outdoors, and an inverter modulates its speed to hold temperature — sipping power once the room is cool. A portable keeps the whole hot machine inside the room, pushes heat out through a hose that leaks warmth back, and most models are simple on/off devices that hammer at full power. The result: a split delivers roughly two to three times the cooling per kilowatt-hour. Over a summer, the running-cost gap partly repays the installation premium — and over ten years it repays a lot of it. The full purchase comparison is in portable vs split.
Five ways to cut the bill (whatever you own)
- Set 24–25°C, not 19°C. Every degree lower adds roughly 5–10% to consumption. 24°C with low humidity feels dramatically better than 30°C — you don't need a meat locker.
- Close the room. Doors, windows, and daytime blinds on sun-facing glass. Cooling air that immediately escapes is the biggest hidden cost.
- Pre-cool on cheap-rate tariffs. If you're on an EV or time-of-use tariff, cooling the room before the peak-rate window starts costs a fraction as much.
- Use dehumidify mode on muggy days. UK discomfort is often humidity, not raw heat — dry mode uses less power and can be all you need.
- Service it. Clogged filters make any system work harder for the same cooling. Clean portable filters monthly in summer; get splits serviced annually (£70–£120).
The winter flip-side
If you own a reversible split system, the running-cost story gets better: as a heat pump it typically delivers 3+ units of heat per unit of electricity, which usually beats plug-in electric heaters by a wide margin for heating a single room. A system you'd have bought for summer alone quietly becomes the cheapest way to heat your home office in January — which changes the value-for-money calculation entirely. More in our full cost guide.
Weighing up an install? Get the real numbers side by side: size your room, then get up to three free quotes from certified installers and compare five-year cost of ownership, not just the sticker price.
Quick answers
Is it cheaper to leave air conditioning on all day?
Almost never in a UK home. Inverter systems are efficient at holding a temperature, but holding it for 24 hours still costs more than cooling the room an hour before you need it. The exception is poorly insulated rooms during multi-day heatwaves, where recovery from very hot takes longer — even then, a timer beats "always on".
How much does air conditioning add to a UK electricity bill per year?
For typical single-room evening use across a British summer — call it 250–400 hours — a split system adds roughly £40–£90 per year and a portable £70–£130. Whole-home or all-day use scales up accordingly.
Does air conditioning use gas or electricity?
Electricity only, in UK homes — the "gas" inside the system is sealed refrigerant, not fuel, and it isn't consumed. Every cost on this page is electrical. (Vehicle AC and some large commercial systems differ, which is where the confusion comes from.)
Do fans cost less than air conditioning?
Massively — a fan costs about 1p per hour. But a fan doesn't cool the air, it moves it; above roughly 27°C the comfort benefit fades. Fans and AC together work well: the fan spreads the cooled air, letting you set the AC a degree or two higher.