Which? uses cookies to improve our sites and by continuing you agree to our cookies policy

How to buy an air conditioner

By Matthew Knight

Put us to the test

Our Test Labs compare features and prices on a range of products. Try Which? to unlock our reviews. You'll instantly be able to compare our test scores, so you can make sure you don't get stuck with a Don't Buy.

How to buy an air conditioner

Air conditioning is now common in offices and shops, but how often do you wish you had air-con in your home?


Family relaxing in an air conditioned living room


In the depths of winter, it can be hard to imagine needing an air conditioner. But at the height of summer, a hot, stuffy house can be very uncomfortable. Cooling down your home should help you get a better night's sleep when the outside temperature is high.

If you'd like to cool your home, but don't need something as powerful as an air conditioner, it's worth considering a good room fan or an air cooler. However, if you've got your heart set on air con, then read on - our guide will help you to choose the best air conditioner for your home.

Which type of air conditioner should I buy?

There are two main types of air conditioner: single-unit models that are portable and need to be vented through a window or door, and split-unit models that are permanently fixed to a wall.

Single-unit air conditioners


  • A fairly cheap fix to cool your home
  • Easy to install
  • You vent hot air out through a hose, so you can move the unit from room to room


  • Venting the hose through an open window could pose a security risk
  • Portable air conditioners are not as effective at cooling as split-unit models – they get hot and leak heat back into the room
  • Some models can be heavy, so make sure your chosen unit isn’t too heavy for you to lift comfortably and that the hand-holds are easy to grip

Split-unit air conditioners


  • Ideal if you have one room that gets very hot
  • A secure way of air conditioning your home – no need to leave windows open
  • Quieter and more efficient than single units
  • Usually more powerful than single units


  • Tend to be more expensive than single units
  • Need to be permanently mounted on an outside wall – installation can be tricky, and you may need to hire a professional

What size air conditioner do I need?

Air conditioners come in various shapes and sizes, but are often described in terms of their BTU (British thermal unit) output. In theory, the higher the BTU claimed, the more efficiently it can cool a room.

In our lab tests we found that few air conditioners met the BTU claimed on the packaging, so we wouldn’t recommend you rely on those claims to make your purchase.

If a machine has a higher cooling capacity, it should cool quickly. But, as a general rule, 5,000 to 8,000 BTUs is adequate for most living rooms or bedrooms.

There's a calculation you can use to work out what BTU is right for you. As a rough guide, multiply the dimensions (in feet) of the room to be cooled by five. So for a 20 x 15 x 12-foot room: 20 x 15 x 12 x 5 = an air conditioner of 18,000 BTUs.

What extra features should I look out for?

Sleep or night modes reduce noise by running the compressor and fan more slowly.

Timer options allow you to set the machine to automatically switch on and off - useful if you want to come home to a cool house or save energy by having the unit switch off once you’ve fallen asleep. Pick a model with a clock and 24-hour setting. Some come with only countdown or delay timers; these need to be reset daily.

Remote controls let you adjust settings without moving from your seat, but are easy to lose. Look for a machine with a dock to store the remote if you're prone to gremlins hiding your things.

Will I be able to maintain it?

These important tasks will keep your air conditioner in good shape:

  • Remove bungs to drain water from portable units at the end of summer, before they are packed away for winter. If the summer has been particularly humid, you may need to drain the unit every few weeks. Water pipes are normally located at the bottom of the machine. Before you buy, check in store that you can bend down and unplug the water pipes easily, as sometimes bungs can be fiddly and difficult to grip.
  • Clean dust filters regularly on both portable and split models. Before buying, ask yourself whether you’ll be able to easily access these parts for cleaning

Does Which? test air conditioners?

We no longer test air conditioners. Our relatively mild UK climate means demand is fairly low, so it's not worthwhile for us to pay the high costs associated with testing these appliances.

For your reference, we've listed older Best Buy air conditioners from our previous tests, which finished in 2011, below. Most of these products are no longer available, but we provide the information to give you an idea of the brands and features that have historically been worth looking out for.

Only logged-in Which? members can view the full results in our table below. If you're not yet a member, you can try Which? for £1 and get instant access.

Previous Best Buy air conditioners
What it looks like Brand and model Type BTU Remote control Price Score

Subscriber only content Split unit 9,210 Yes Subscriber only content 91%
This air conditioner is camouflaged as a picture frame, which you can customise with your own photograph or print.

It's highly effective at cooling quickly and quietly, it dehumidifies well and has a heater function for all-year-round use.

Subscriber only content Split unit 12,000 Yes Subscriber only content 87%
This model has lots of mode options that you can set to your own personal taste. A digital display on the main body and the remote control shows your mode selections as well as the temperature you've set.

It's great at cooling and dehumidifying. The airflow on full blast is strong enough to be felt at least a metre away

Subscriber only content Single unit 13,000 Yes Subscriber only content 83%
You can add water to this air conditioner to enhance cooling ability and reduce noise.

It is highly effective at cooling and dehumidifying. It's quite heavy, though, so you won't want to carry it up and down stairs.

Subscriber only content Single unit 10,000 Yes Subscriber only content 75%
This air conditioner is very portable, with a good handle for gripping.

It has lots of functions, including dehumidification, varying fan speeds and night modes that reduce noise.

Subscriber only content Single unit 9,000 No Subscriber only content 74%
There's no remote control or night mode, but there is a countdown timer.

It cools fast and dehumidifies really well, but the bung on the water pipe is tricky to release.

Subscriber only content Single unit 8,000 Yes Subscriber only content 71%
This air conditioner has a number of useful features, including a countdown timer and a dehumidifier function.

It cools and dehumidifies well, but it is rather noisy and doesn't have a sleep mode to reduce noise at night.

Table notes: These air conditioners were tested in 2008 and may no longer be available. Each model was rated on cooling capacity, energy efficiency, dehumidification, noise and controls. We no longer test air conditioners.