Air conditioning units · current figures
Last updated 2026-06-24~30p
an hour, typical portable
~17p
an hour, fitted split
£1,500+
to fit a split system
24.67p
per kWh (price cap)
Electricity rate: Ofgem price cap, 1 April to 30 June 2026, Direct Debit (Ofgem). Running costs assume a 1,200 W portable and a 2.5 kW split system at typical UK ratings. Install prices: mainstream UK fitters, mid-2026 [verify each quarter].
The four types of air conditioning unit, and which is worth buying
Every air conditioning unit on sale in the UK is one of four kinds. They do the same job, moving heat out of your room, but they differ hugely in price, running cost and hassle. The table below is the honest version: not "which is best" in the abstract, but which fits which situation.
| Type | Buy price | Run cost | Fitting | Best for |
|---|---|---|---|---|
| Portable (monobloc) | £250 to £600 | ~26 to 35p/hr | No install; vent a hose out a window | One room, occasional hot spells, renters. The easy buy, but the dearest to run and the noisiest. |
| Fixed split system | £1,500 to £3,000 fitted | ~15 to 20p/hr | Pro install; indoor unit + outdoor box | A room you cool often. Quiet, efficient, and it heats in winter too (it is a heat pump). |
| Multi-split | £2,800 to £4,500 fitted | ~15 to 20p/hr per room | Pro install; one outdoor box, several indoor units | Two or more rooms from a single outdoor unit. Best cost-per-room if you cool the whole home. |
| Window unit | £200 to £450 | ~20 to 30p/hr | Sits in an open sash window | Rare in the UK (our windows rarely suit them). Cheaper to run than a portable, but a security and noise trade-off. |
The pattern is the one nobody puts on the box: the cheaper the unit, the dearer it is to run. A portable is the lowest price on the shelf and the highest cost per hour. A fitted split is the opposite. Which is right for you depends almost entirely on one thing, how many hours a year you will actually run it.
What size air conditioner do you need?
Size is measured in BTU (British Thermal Units), the unit's cooling power. Too small and it runs flat out and never cools the room; too big and it short-cycles, leaving the air cold and clammy. The sweet spot is roughly 20 BTU per square foot of floor, nudged up for sun and glass. Tell the sizer your room and it gives you the number to shop with.
What size air conditioning unit do you need?
Enter your room size and how sunny it is. We work out the cooling power (BTU) to shop for, plus the rough cost to run it.
You should shop for about
Unit to look at
Portable, per hour
Split, per hour
Rule of thumb: ~20 BTU per square foot, +10% for a sunny room. Costs at the 24.67p price cap, a portable at ~1,200 W and a split at ~750 W for the matched room. A guide, not a survey — verified June 2026.
The belief that costs people money
The common assumption is "buy the most powerful air conditioner I can afford, more BTU means cooler". It is the opposite of true. An oversized unit cools the air fast, then switches off before it has pulled the moisture out, so the room feels cold and damp, and the unit short-cycles, which wears it out and wastes energy. The right size, matched to the room, runs longer and gentler and actually feels better. Bigger is not cooler; matched is cooler.
The second costly belief is that the sticker price is the price. With air conditioning, the buy price is the small number. A £350 portable run through three hot summers can burn more in electricity than a £1,800 split would, and the split keeps your home warm in winter on top. The real cost is buy price plus years of running cost, and on that measure the cheap option often loses.
Why most air conditioning guides get it wrong
Search "best air conditioning unit" and you mostly get affiliate lists ranking ten portables by star rating. Two things are missing from almost all of them:
- ✓They rank by buy price and reviews, never by cost to own. The "best value" portable is often the most expensive choice over three years once you count the electricity.
- ✓They treat air conditioning as a summer-only purchase. A reversible unit heats in winter more cheaply than any electric heater, which changes the whole value calculation, and it is the one point that would tip a borderline buyer.
This guide does the opposite: it sizes the unit to your room, prices it at your electricity rate, and tells you when a fan or a portable is genuinely the smarter buy than a full system.
The insider view: your air conditioner is a heat pump running backwards
Here is the fact that reframes the whole purchase. An air conditioner does not make cold. It is a heat pump, the same machine in your fridge, that grabs heat from inside your room and dumps it outside. "Cooling" is just moving heat the other way. And because it only moves heat rather than generating it, it shifts roughly three units of heat for every one unit of electricity it draws. That is why a fitted split costs about half as much per hour as a portable doing the same job: the portable wastes effort fighting its own warm exhaust, while the split quietly pumps heat across the wall.
The winter trick most buyers miss A reversible split system runs the pump backwards in winter: it pulls warmth from the cold outside air and pushes it into your room. In that mode it is an air-to-air heat pump, and it can deliver around 3 kWh of heat per 1 kWh of electricity, far cheaper than a 1 kWh-for-1 kWh plug-in electric heater. So the same box you bought to survive a heatwave can cut your winter heating bill. Because it counts as a heat pump, an installed reversible system may also qualify for 0% VAT on supply and fitting until 31 March 2027 (it returns to 5% after). HMRC assesses these case by case and the rule for air-to-air systems has shifted, so ask your installer to confirm before you bank on it.
This is the lens that should drive the decision. A portable is a cooling-only gadget you store in a cupboard all winter. A fitted reversible split is a year-round heating and cooling machine. If you only ever cool a spare room for two weeks in July, the gadget is fine. If you would use it across the seasons, the heat pump is doing two jobs for one install.
What it really costs: to buy, to install, to run
Three numbers decide the true cost of an air conditioning unit: what you pay for it, what fitting costs, and what every hour of cooling adds to your bill. The first two are one-offs; the third repeats for years, which is why it deserves the most attention. The calculator below prices the running cost at your electricity rate, and our dedicated portable air conditioner running cost guide goes deeper on the cheapest type to buy and the dearest to run.
What will your air conditioning cost to run?
Costs you about
a year · · £
Each
A month
Cheapest live electricity rate
British Gas is offering 23.85p per kWh — about 3% below the 24.67p price cap. Apply it to see every cost above drop.
A lower unit rate cuts the cost of every appliance above at once.
Default unit rate: Ofgem price cap, 1 April to 30 June 2026, Direct Debit. Costs are estimates based on typical power ratings.
Every appliance at a glance
at the 24.67p/kWh price cap| Appliance | Power | Typical use | kWh/yr | Per use | Per year |
|---|---|---|---|---|---|
| Air fryer | 1,500 W | 30 min, 5×/wk | 195 | 18.5p | £48 |
| Electric oven | 2,100 W | 60 min, 5×/wk | 546 | 51.8p | £135 |
| Broadband router | 10 W | all day, 7×/wk | 87 | 5.9p | £22 |
| TV (50-inch LED) | 90 W | 300 min, 7×/wk | 164 | 11.1p | £40 |
| Tumble dryer | 2,500 W | 90 min, 3×/wk | 585 | 92.5p | £144 |
| Washing machine | 1,000 W | 60 min, 4×/wk | 208 | 24.7p | £51 |
| Dishwasher | 1,200 W | 90 min, 4×/wk | 374 | 44.4p | £92 |
| Kettle | 3,000 W | 3 min, 21×/wk | 164 | 3.7p | £40 |
| Fridge-freezer | 17 W | all day, 7×/wk | 149 | 10.1p | £37 |
| Electric heater | 2,000 W | 240 min, 7×/wk | 2,912 | £1.97 | £718 |
| Portable air conditioner | 1,200 W | 240 min, 7×/wk | 1,747 | £1.18 | £431 |
| Split air conditioner | 750 W | 240 min, 7×/wk | 1,092 | 74.0p | £269 |
| Electric shower | 8,500 W | 10 min, 7×/wk | 516 | 34.9p | £127 |
| Desktop / gaming PC | 200 W | 240 min, 7×/wk | 291 | 19.7p | £72 |
All figures at the Ofgem price-cap electricity rate of 24.67p per kWh (1 April–30 June 2026, Direct Debit). Standing charges are paid whether or not you switch anything on, so they are not included here. Change the rate in the calculator above to re-price every row for your own tariff. The cheapest live electricity rate we can see today is 23.85p per kWh from British Gas, about 3% below the cap; at that rate every cost above falls by roughly the same share.
What you should actually do
Size before you shop
Use the room sizer to get your BTU number first. Buying by "looks powerful enough" is how people end up with an oversized, clammy, short-cycling unit.
Count the years, not the shelf price
Add three years of running cost to the buy price. A cheap portable used often can cost more to own than a fitted split that also heats in winter.
Decide if you cool or cool-and-heat
Occasional summer use only? A fan or portable is the smart buy. Year-round use? A reversible split (air-to-air heat pump) does two jobs for one install.
Check your unit rate before anything
Every hour of cooling is priced at your electricity rate. A cheaper rate per kWh cuts the cost of the AC and everything else you own, with no change to how you live.
The bottom line
An air conditioning unit moves heat; it does not make cold. That is why the cheap portable is the dearest to run, why an oversized unit cools worse than a matched one, and why the unit worth buying for year-round use is a reversible split, an air-to-air heat pump that cools in summer and heats in winter for about a third of the electricity a plug-in heater would burn. Size it to your room, price it at your own rate, and judge it on the cost to own over years, not the number on the shelf. With UK summers getting hotter, this is a purchase more homes will make, so make it the informed way.
Air conditioning FAQ
The Selectra expert answers your questions
As a rule of thumb, you need about 20 BTU of cooling for every square foot of floor. A small bedroom (around 10 m², or 110 sq ft) needs roughly a 5,000 to 7,000 BTU unit; an average living room (around 20 m²) needs about 9,000 to 12,000 BTU. Add 10% for a sunny, south-facing room or one with lots of glass. Use the room sizer above to get your number, then never buy bigger than you need: an oversized unit short-cycles, cools unevenly and wastes money.
For a few stuffy weeks a year, a fan or a portable unit is usually enough and far cheaper. Air conditioning becomes worth it when you use it a lot, or want one box that cools in summer and heats in winter. A fitted reversible split system is an air-to-air heat pump: in heating mode it can deliver around 3 units of warmth for every unit of electricity, which is cheaper than any plug-in electric heater. If you would use it year-round, the sums change in its favour.
At the 2026 price-cap rate of 24.67p per kWh, a typical portable air conditioner (around 1,200 W) costs about 30p an hour; a fitted split system costs roughly 15 to 20p an hour for the same room, because a heat pump moves heat rather than making it. A fan costs under 2p an hour. See our portable air conditioner running costs guide for the full breakdown.
A single fitted split system typically costs £1,500 to £3,000 installed; a multi-split covering two or more rooms is around £2,800 to £4,500. Installation is most of the cost. Because a reversible unit counts as an air-to-air heat pump, the supply-and-install job may qualify for 0% VAT until 31 March 2027 (it reverts to 5% after) — confirm eligibility with your installer, as HMRC treats these cases individually.
A portable wins on price and flexibility: nothing to install, move it room to room, ideal for renters or a few hot weeks. A fixed split wins on everything that costs money over time: it is quieter, cools better, runs at about half the cost per hour, and heats in winter. Buy portable for occasional use, fixed if you will cool the same room often.
More than most appliances, because it runs for hours and cooling is hard work. A 1,200 W portable left on for an 8-hour day uses about 10 kWh, or roughly £2.40. The single biggest saving is not the unit you buy but your electricity rate: a cheaper rate per kWh cuts the cost of every hour you run it.