How to buy a portable air conditioner in the UK

How many BTUs before I stop sweating?

BTU (British Thermal Units per hour) is the number that decides whether a cooler will actually win against your room or just hum along politely while you melt. Buy too few and the unit runs flat out and never quite gets there; buy wildly too many and you’ve overspent on a machine that short-cycles. The whole game is matching capacity to the space.

A reasonable starting point for a typical, reasonably insulated UK room is around 350 to 450 BTU per square metre. Then nudge it up for the things that quietly add heat: a south-facing room with big windows, a top-floor or loft conversion that bakes by mid-afternoon, a kitchen, or a room packed with computers and people. The table below turns all that into bands you can actually shop against.

Portable, split or evaporative?

Portable units are what most people mean by a portable air conditioner: a free-standing box on castors with a hose that vents hot air out of a window. No installation, no waiting for a fitter, no permanence: wheel it in, plug it in, point the hose out the window. The trade-off is the noise and the slightly undignified faff of the window-sealing kit.

Split systemsbanish the noisy compressor to the outside wall and leave a quiet unit indoors. They cool better, run quieter and sip far less power, but they need a professional to install them and they’re a fixture, not something you stash in the loft come October. Worth it if you’re cooling the same room every summer for the foreseeable future.

Evaporative coolers are the cheap, low-power tempting option, and a trap on the exact day you need them. They cool by evaporating water, which works a treat in dry heat and does almost nothing in a muggy British summer except make the room damp. A useful gadget for an Arizona garage; a disappointment in a Manchester bedroom in July.

Single hose vs dual hose (the boring detail that actually matters)

Everyone skips this one and then wonders why the room never quite cools. A single-hose portable uses your already-cooled room air to chill its own internals and blows it out the window, which drops the pressure indoors and draws warm air straight back in through every gap, vent and badly fitting door. It’s cooling the room and undermining itself at the same time. A dual-hose unit pulls its condenser air from outside through a second hose, so it stops competing with itself. Dual hose costs a bit more and the units are chunkier, but they bring a hot room down noticeably faster.

Energy rating and running costs (the bill comes later)

Cooling is energy-hungry, so that efficiency label is real money by September. Check the energy rating and the input power in watts. A 9,000 to 12,000 BTU portable typically pulls somewhere between 0.8 and 1.3 kW while it’s actively cooling. The reassuring bit: it won’t run flat out all day. Once the room hits your set temperature it cycles down, which is why a correctly sized unit ends up cheaper to run than an undersized one straining heroically and losing.

Will the neighbours hear it? (and other anxieties)

A portable air conditioner shares a room with you, usually a bedroom, so the decibel figure is worth more than a glance. Anything in the high 40s to low 50s dB(A) is normal; below that is genuinely quiet; anything pushing the high 50s and beyond is the audio equivalent of trying to sleep beside a small, motivated hairdryer. Most models offer a night or sleep mode that drops the fan speed so you can actually nod off. The neighbours, for what it’s worth, will hear the outside hose long before they hear the unit.

Heating, Wi-Fi and the extras

Plenty of portables double as heaters via a reverse cycle, which quietly earns the unit its keep for the other eleven months of the British year. Wi-Fi and app control are genuinely useful for pre-cooling a bedroom before you turn in, so you’re not climbing into a warm room and waiting it out. All nice to have, none of it a dealbreaker: nail the size and hose setup first, then weigh the gadgetry.

Buying during a heatwave (a.k.a. the sprint)

Here’s the catch nobody warns you about: the second a heatwave is forecast, every decent unit evaporates faster than the will to work. Stock runs out within days and you’re left choosing between the dregs and a delivery slot that lands well after the hot spell ends. Two things save you. First, decide your BTU band and hose configuration beforeyou need it, so you’re not frantically Googling “dual hose meaning” at 2am in a 28-degree bedroom. Second, check live availability across several retailers at once rather than F5-ing a single shop, and when a suitable unit shows up in stock with quick delivery, buy it then and there. That cross-retailer, in-stock-first view is the whole reason Aircon Wars exists.

Frequently asked questions

How many BTU do I need for my room?

As a rough rule, allow around 350 to 450 BTU per square metre for a normal UK room, then add capacity for sun-facing rooms, top floors and lots of electronics. A 12 to 18 m² bedroom is usually fine on a 7,000 to 9,000 BTU unit; a 25 m² living room wants 12,000 BTU or more. Round up if in doubt: nobody has ever stood in a cool room and wished it were warmer.

Is a dual-hose portable air conditioner worth it?

Usually yes. A single-hose unit pulls room air to cool its condenser and pushes it outside, which creates negative pressure that quietly sucks warm air back in through every gap, so it's a bit like bailing out a boat that's still got a hole in it. A dual-hose unit draws condenser air from outside instead, so it isn't fighting itself. It costs a little more and it's a chunkier machine, but it cools faster and works harder for it.

Will an evaporative cooler work in the UK?

Only sometimes, and not on the day you'll most want it to. Evaporative (swamp) coolers chill air by evaporating water, so they work best when the air is dry, which is not a phrase often used to describe a British summer. On a muggy heatwave day they do very little except add humidity, leaving you damp as well as hot. They're cheap to run, but think of them as a fan with ambitions, not a true air conditioner.

Do portable air conditioners use a lot of electricity?

They're among the thirstier appliances in the house. A typical 9,000 to 12,000 BTU portable draws roughly 0.8 to 1.3 kW while it's actively cooling. Check the energy rating and the input wattage, and take comfort in this: the unit cycles off once the room hits temperature, so a correctly sized model costs less to run than an undersized one wheezing away at full pelt all afternoon.

Why is everything sold out, and how do I find one in stock?

Because the entire country has the same idea on the same morning. Demand spikes the instant a heatwave is forecast and retailers sell through stock in days, sometimes hours. The fix is to check live availability across several retailers at once rather than refreshing one shop like it owes you money, then buy the moment you find a suitable unit in stock. That cross-retailer, in-stock-first view is the whole reason Aircon Wars exists.

Prices, stock and specs shown elsewhere on Aircon Wars are indicative and refresh periodically. See how we source them in our methodology.