Three hot summers in a row have turned air conditioning from a holiday luxury into something UK homeowners actually price up at home. With the July 2026 price cap putting the average electricity unit at 26.11p per kWh, the real question is not whether you can buy a unit, but what it does to your bill once the heatwave sets in.
Here is the direct answer on air conditioning running cost UK homeowners can plan around: a typical portable unit drawing around 1kW costs roughly 26p an hour to run, so eight hours on a hot day is about £2. A small 7,000 BTU portable comes in nearer 20p an hour; a larger 12,000 BTU model or a multi-room split system can push 30–40p an hour or more. Over a two-week summer hot spell, most homes are looking at £20–£45 — not the hundreds people fear, but not nothing either.
The one calculation that tells you everything
Every running-cost figure comes from the same simple sum: power used in kilowatts, multiplied by hours run, multiplied by your unit price. So a 1kW unit run for 5 hours at 26.11p costs 1 × 5 × 26.11 = about £1.31.
The number people get wrong is the power rating. The big "BTU" figure on the box — 7,000, 9,000, 12,000 — is the cooling output, not the electricity the unit draws. A 9,000 BTU portable typically pulls around 0.9–1.0kW from the wall; a 12,000 BTU model around 1.2–1.4kW. Always find the wattage (W) or input power on the label or in the manual, divide by 1,000 to get kilowatts, and use that in the sum. If a listing only quotes BTU and hides the wattage, treat that as a warning sign.
What each type actually costs in 2026
Portable single-hose units
These are the £250–£500 units you wheel between rooms. A 7,000 BTU model around 780W costs roughly 20p an hour; a 9,000–12,000 BTU model costs 24–37p an hour. They are the cheapest to buy and the least efficient to run, partly because the single exhaust hose pulls warm air back into the room through gaps. Run one for six hours an evening across a 14-day hot spell and you are looking at roughly £17–£31.
Fixed split-system air conditioning
A wall-mounted split system — an outdoor compressor feeding one or more indoor units — is far more efficient. The inverter compressor cools the room quickly, then throttles back to a trickle rather than cycling fully on and off. A single-room 3.5kW (12,000 BTU) split might draw 0.8–1.0kW at full tilt but spend most of its time well below that, so real-world running often works out cheaper per hour of comfort than a portable, despite the bigger cooling output. Installation by an F-Gas registered engineer is the catch: expect £1,500–£3,000-plus for a single room.
Whole-home or multi-split systems
Cooling several rooms through a multi-split or ducted system multiplies both the comfort and the bill. Running two or three indoor heads through a warm week can add £40–£80 to a quarter's electricity. These systems make most sense in homes that will also use them for heating in winter, where the same kit runs as an air-source heat pump.
The honest take on whether it is worth it
Here is the blunt version: for most UK homes, a portable unit you run for two or three weeks a year is a sensible, cheap comfort buy, and the running cost is the least of your worries. But if you are tempted by a fixed split system purely for cooling, stop and think about the EPC and the whole year. Air conditioning is an electrical load your Energy Performance Certificate assessor will note, and cooling-only kit does nothing for your rating or your winter bills. If you are going to spend £2,000-plus, buy a reversible air-to-air heat pump that also heats the house in winter — otherwise you are paying split-system money for two weeks of use.
Five ways to cut the running cost
The unit price is fixed by your tariff, but how much electricity you burn is not. The cheapest cooling is the heat you keep out in the first place.
Close curtains and blinds on the sunny side of the house before the room heats up — shading south and west-facing windows in the morning does more than any setting on the unit. Set the thermostat to 24°C rather than 18°C; every degree lower is more compressor time and more pence. Seal the gap around a portable unit's exhaust hose with a window kit so it is not fighting warm air leaking back in. Service or clean the filters, because a clogged filter makes the unit work harder for the same cooling. And cool only the room you are in rather than the whole house — a closed door is free.
What to do in the next 30 minutes
• Find the input wattage of any unit you own or are eyeing up, and divide by 1,000 to get its kilowatts.
• Multiply that by your real unit rate (check your latest bill — it may differ from the 26.11p average by region) and by the hours you would actually run it.
• Walk the house at the hottest part of the day and note which windows let the most sun in — those are your priority for blinds or shading.
• Check the energy label or product page for the cooling EER or SEER; higher is more efficient and cheaper to run.
• Log your unit's wattage and your summer cooling hours in Home+ so you can compare this year's spell against next year's.
Frequently asked questions
How much does it cost to run air conditioning per hour in the UK?
At the July 2026 average unit rate of 26.11p per kWh, a 1kW portable unit costs about 26p an hour. Smaller 7,000 BTU units cost nearer 20p an hour, while larger or multi-room systems can run to 30–40p an hour or more.
Is it cheaper to run a portable or a fixed air conditioner?
Per hour of genuine comfort, a fixed inverter split system is usually more efficient because it cools faster and then idles. A portable is far cheaper to buy and fine for occasional use, but it works the unit harder and wastes cooling through the exhaust hose.
Does air conditioning use a lot of electricity?
Less than people expect for occasional use. A single room cooled for a few hours a day over a summer hot spell typically adds £20–£45 to your bill. Whole-home or all-day running is where the cost climbs.
Will air conditioning affect my EPC rating?
Cooling-only air conditioning is an electrical load and does nothing to improve your EPC. A reversible air-to-air heat pump that also heats the home can, however, be a more efficient way to heat than older electric or gas systems and is the better buy if you are fitting a fixed unit.
What is the cheapest way to keep cool without air conditioning?
Shading windows before the room heats up, cross-ventilating at night and in the early morning, and using a fan to move air all cost a fraction of cooling. A fan typically uses 30–70W against a portable AC's 1,000W.
Air conditioning is one of those costs that creeps up quietly across a hot fortnight and is forgotten by autumn — until the next heatwave, when you are guessing all over again. Track your running costs in Home+ by logging your unit's wattage and the hours you run it, alongside your other appliance and energy notes, so next summer you are working from your own numbers rather than a worst-case headline.
