How to choose a portable air conditioner

Choose a portable air conditioner by working through the same seven checks in order. The first, size, matters most: a unit that is too small never catches up with a heatwave, and one that is too large cycles on and off, cools unevenly and wastes money.

Not sure of your room? Use the BTU calculator, which also adjusts for sun, insulation, people and heat-producing appliances.

BTU (British thermal unit) measures how much heat a portable air conditioner can remove in an hour. One kilowatt of cooling is about 3,412 BTU, so a unit sold as 9,000 BTU removes roughly 2.6 kW of heat.

Our rule of thumb, which the calculator uses, is about 180 BTU per cubic metre of room volume, plus 500 BTU for each person and each heat-producing device. A 4.5 m × 3.5 m room with a 2.5 m ceiling is 39 m³, or about 7,100 BTU before people and electronics, and about 8,600 BTU with two people and a TV. Add around 15% for a sunny, south-facing room and about 20% for poor insulation or a room under the roof.

A single-hose unit vents hot air outside but uses room air to cool its own condenser, so warm air leaks in to replace it. A dual-hose unit uses outdoor air for the condenser and returns it outside, so no room air is wasted. In practice dual-hose designs cool faster and hold a lower temperature on hot days, at a higher price and with a wider window kit.

Choose single-hose for a room under about 15 m², occasional use and a budget under £350. Choose dual-hose for larger rooms, regular use and the hottest, sunniest rooms. The full comparison is in single vs dual hose.

Portable units are rated by their energy efficiency ratio (EER): cooling output divided by electricity input. Under the UK energy label rules, a single- or double-duct unit rated class A has an EER between 2.60 and 3.10, and class A+ sits between 3.10 and 3.60. Higher is better, but the gap between neighbouring classes is modest, so noise and size usually matter more than a single class.

What matters at the meter is wattage. Units typically draw 0.75 kW to 1.5 kW. At the October to December 2026 price cap of 26.32p per kWh, a 1 kW unit costs about 26p an hour to run flat out. Work out your own figure with the running cost calculator, and read our energy efficiency guide for how to cut it.

The compressor sits in the same room as you, so noise is the biggest day-to-day complaint about portable air conditioners. Rated noise for the 49 portable models in our catalogue has a median of 55 dB, with the quietest at 47 dB.

For sleeping, look for a sleep mode that lowers fan speed and raises the target temperature gradually. Our noise levels guide explains the numbers, and the sound meter lets you measure a unit in your own room.

Every portable air conditioner needs a window to vent through, and the standard kit is designed for a window that slides sideways. Most British homes have something else.

• Sash windows open vertically, so a standard kit does not fit. You need a rigid panel or a sash-specific kit. See portable air conditioners for sash windows.
• Casement windows open outwards on hinges. A panel kit fitted into a gap, or a hose through a tilted window, works well.
• uPVC tilt-and-turn windows can take a panel kit in the tilt position. Check the hinge can carry the weight.
• Roof windows and conservatories need a longer hose or a purpose-made kit.

Also check the hose length (usually 1.2 to 1.5 m) reaches from where you want the unit to the window without sharp bends.

Of the 49 portable models in our catalogue, 37 list app or smart control and 14 offer a heating mode. Useful extras are worth paying for only if you will use them.

• Dehumidify mode removes moisture without cooling as hard. Valuable in humid British weather and for drying laundry.
• Timer and sleep mode are the features that actually save electricity and sleep.
• Self-evaporating design means fewer trips to empty the tank, though in very humid weather you may still need to drain it.
• App control and voice assistants are handy for pre-cooling a room before you get home, but add cost and a Wi-Fi dependency.
• Refrigerant: newer models use R32 or R290, which have a far lower global warming impact than older R410A.

The median price across our portable models is £409.99, with a range of £256.99 to £3,999.95. Under £300 expect louder compressors and basic controls. Between £300 and £450 you get most of the useful features. Above that you are paying for capacity, dual hoses, quieter operation or smart control.

Prices are from UK retailer listings checked in April 2026 and change often, especially around heatwaves. Treat them as a guide and check the retailer before buying.

• Sizing by the box. A 12,000 BTU label does not guarantee 12,000 BTU of real cooling.
• Ignoring the window. A great unit with the wrong kit leaks hot air back in and loses much of its cooling.
• Buying on price alone. The cheapest unit is often the loudest and the least efficient; over a few summers the difference shows up on the electricity bill.
• Oversizing. A unit far too large for the room cools quickly, shuts off and leaves the air clammy because it never runs long enough to dry it.
• Skipping upkeep. A clogged filter is the most common reason cooling fades. Our maintenance guide takes five minutes a fortnight.

Once you have a shortlist, set up and seal the window kit properly. Our installation guide shows how.