Costs
8 min readWhat air conditioning actually costs to run
Roughly 25p an hour to cool a room, and about a quarter of the cost of a plug-in heater to heat one. The arithmetic, the assumptions behind it, and the temperature at which it stops being cheap.
The short answer
Cooling a room costs roughly 25p an hour — a 3.5kW unit draws about 0.8–1.1kW while it’s pulling the temperature down, and much less once it’s holding it. Heating is where it gets interesting: the same unit delivers about three to four units of heat for every unit of electricity, which makes it roughly a quarter the cost of a plug-in electric heater and broadly line-ball with running a gas boiler — until the outside temperature drops below about −10°C, when the advantage disappears.
Cooling, in July
A 3.5kW wall split — the size that suits a typical double bedroom or a small living room — draws around 0.8 to 1.1kW while it's actively cooling. Once the room reaches temperature the compressor throttles back and consumption drops well below that, often to a third.
| Usage | Electricity | Cost |
|---|---|---|
| An hour pulling the room down | ~1.0 kWh | ~25p |
| An hour holding temperature | ~0.35 kWh | ~9p |
| A hot evening, 18:00 to midnight | ~2.5 kWh | ~63p |
| Overnight in a bedroom, 8 hours | ~3.2 kWh | ~80p |
| A two-week heatwave, evenings and nights | ~50 kWh | ~£12.50 |
Which is the point most people find surprising: the electricity for a full British heatwave costs less than a takeaway. Running cost is not the reason people hesitate over air conditioning, and any page that spends its length reassuring you about it has misread the question.
The objection this page is really about
“how many days do we need to use them in the UK? Paying £5K for something you use 2 weeks a year is pretty expensive.”
This is the objection, and notice what it's actually about. It isn't the running cost and it isn't really the price. It's the price divided by the number of days you'd use it. At two weeks a year, no capital cost looks reasonable.
The answer isn't a discount. It's that the premise is wrong — the same unit is a heater, and a very efficient one. Once you count the days it earns its keep in heating mode, the divisor changes from fourteen to something closer to a hundred and fifty.
Heating, which is the real argument
A heat pump doesn't make heat, it moves it, which is why it can deliver more energy than it consumes. In mild conditions — 5°C to 15°C outside, which is most of the British heating season — a modern air-to-air unit returns three to four kilowatts of heat per kilowatt of electricity.
| Method | Efficiency | Cost per kWh of heat |
|---|---|---|
| Air-to-air heat pump | 350–400% | ~6–7p |
| Gas boiler heating the whole house | ~90% | ~8p, plus every other room |
| Plug-in electric heater / panel heater | 100% | 25p |
| Oil-filled radiator | 100% | 25p |
Per kilowatt-hour delivered, air-to-air heating is roughly level with gas and about a quarter the cost of any form of direct electric heating. The bigger saving usually isn't in that comparison at all, though — it's in not firing a boiler that heats seven rooms in order to make one of them usable.
“10kWh a day using electric heaters...now with Air Heat Pump it's been 1.7-2.9kWh per day.”
That owner's numbers work out at about £2.50 a day before, and 43p to 73p a day after — a saving of roughly £1.80 to £2.05 for every day of the heating season. Across a five-month season that's somewhere near £280. We're quoting one household's metered figures rather than a modelled average, so treat it as an illustration of the scale rather than a promise about your house.
“it really does work out 4x cheaper — which is incredible”
Where the saving actually comes from
Not July, and not January. The months that pay for the unit are the ones either side of winter — roughly late September to November, and February to April — when one room is uncomfortable and heating the whole house to fix it is absurd.
- Days a year you'd plausibly cool
- 15–30Evenings and nights in a warm summer
- Days a year you'd plausibly heat one room
- 120–180Shoulder months and mild winter days
- Time to reach temperature
- 10–20 minAgainst roughly an hour for a wet radiator system
- Typical annual running cost, one room
- £90–160Combined heating and cooling, moderate use
It also responds in minutes rather than the best part of an hour, which changes how you use it. A radiator system heating a whole house is something you commit to for an evening. A single-room heat pump is something you switch on because you're cold now.
The honest ceiling
Efficiency falls as the outside temperature drops, because there's less ambient heat available to move. This is real, it's physics rather than a product flaw, and it's the part most sellers leave out.
| Outside temperature | Roughly what you get back | Cost per kWh of heat |
|---|---|---|
| 10°C | 4.0–4.5× | ~6p |
| 7°C | 3.5–4.0× | ~7p |
| 2°C | 2.5–3.0× | ~9p |
| −5°C | 1.8–2.2× | ~12p |
| −10°C and below | ~1× | ~25p — no better than a fan heater |
What this means for the purchase
If you'll only ever run it in a heatwave, the honest answer is that the capital cost is hard to justify on economics alone — you'd be buying comfort, which is a perfectly good reason, but not a financial one.
If you’ll use it as a heater for one room through the shoulder months, the arithmetic is very different, and the payback comes from heating rather than cooling. That’s worth knowing before you choose a size or a position — an undersized unit run flat out is markedly less efficient than a correctly sized one loafing. Our seven-question flow sizes it, and the pricing page has the installed costs without a phone call.
One more thing worth checking before you buy: there is a £2,500 grant for air-to-air heat pumps, but it excludes any property with fossil fuel heating, which rules out most homes with a gas boiler. We’ve set out who actually qualifies.
Where this comes from
We’d rather you checked. These are the primary sources behind the claims above, in the order they matter.
- Manufacturer performance data — 3.5kW reverse-cycle wall splitsInput power in cooling and declared SCOP/SEER figures for the current Daikin, Mitsubishi and Toshiba domestic ranges.
- MoneySavingExpert forums — owner-reported consumptionMetered day-rate figures volunteered by UK owners across two threads, August 2026. Small sample; quoted as reported.
- Ofgem energy price capSource for the unit rate assumed throughout. Check the current cap before relying on the totals here.
Not yet independently reviewed. This guide was written from the primary sources listed above and is accurate to the best of our understanding on the date shown. It hasn’t been checked by an independent compliance professional, and it isn’t legal advice. Where a decision turns on it, verify with your local authority or with Ofgem directly — and tell us if we’ve got something wrong.