What is the most important thing to check before buying?

Capacity. If the BTU rating does not match your room, nothing else matters much — the unit will either struggle or short-cycle. Work out the right BTU for your room first, then use the rest of the checklist to choose between suitable models.

Single hose or dual hose — does it matter?

It can. A single-hose portable expels warm air outside but draws replacement air from inside the room, which can create slight negative pressure and pull in warm air from elsewhere. A dual-hose unit draws its exhaust air from outside, so it is generally more efficient, though usually pricier and bulkier.

How quiet should a portable air conditioner be?

Noise is measured in decibels (dB). Many portables sit somewhere in the high-50s to mid-60s dB on full power. For a bedroom, look for a lower figure or a dedicated quiet/night mode; for a living room or office, a slightly higher level is usually tolerable.

Air conditioner buying checklist

Before you buy an air conditioner, run through this checklist. In short: get the BTU right for your room, then weigh up hose design, noise, energy efficiency, drainage, window fit, portability and the extra modes you will actually use. Capacity comes first — everything else is about choosing between units that are already the right size.

1. Size and BTU

Make sure the unit’s cooling capacity suits your room. Too small and it never copes on a hot day; too large and it short-cycles and leaves the room clammy. Measure your room and check the right figure with our BTU calculator before you shortlist anything.

2. Single hose vs dual hose

For portables, check whether the unit is single- or dual-hose. Single-hose models are cheaper and lighter but draw replacement air from the room, which can pull warm air in from elsewhere in the house. Dual-hose models take their exhaust air from outside and tend to cool more efficiently, at the cost of size and price.

3. Noise level (dB)

Check the quoted noise figure in decibels. The difference between a unit in the high-50s and one in the mid-60s is very noticeable in a quiet room. If you plan to run it in a bedroom, prioritise a low figure or a proper night mode.

4. Energy rating and efficiency (EER)

A better energy rating, and a higher EER (Energy Efficiency Ratio), means more cooling per unit of electricity. Over a summer of use this affects your bills, so it is worth comparing. Use the running cost calculator to see what the difference means in pounds.

5. Drainage and self-evaporation

Portables remove moisture from the air, which has to go somewhere. Check how the unit handles it: many modern units are largely self-evaporating and rarely need emptying, while others collect water in a tank you must drain, or need a continuous drain hose. If you do not want to empty a tank mid-heatwave, favour a self-evaporating design.

6. Window-kit fit

The exhaust hose needs to vent outside, usually via a supplied window kit. Check the kit suits your windows — sliding, sash and casement windows all differ, and very large or awkward openings may need extra sealing. Confirm the kit works with your window before you buy.

7. Portability and practicalities

If you intend to move the unit between rooms, check its weight and whether it has decent castors and a handle. Also confirm the exhaust hose is long enough to reach your window from where the unit will stand.

8. Useful extra modes

Many units double as a dehumidifier and a fan, and some offer heating too. A dehumidify mode is genuinely useful in a damp UK home outside the cooling season, so a unit that earns its keep year-round can be better value than a cooling-only model.

Ready to shortlist?

Work through the list above, get your target BTU from the BTU calculator, estimate the bills with the running cost calculator, then compare current models in our best portable air conditioners roundup.