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.
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.