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How to buy the best air conditioner

By Aaron West

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How to buy an air conditioner

In the depths of winter, it can be hard to imagine needing an air conditioner in the UK. 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 it's muggy outside.

In this article

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

There are all different types and brands on the market, suited to all kinds of homes and budgets. And with words like 'standalone', 'split-unit', 'BTU' and 'refrigerant' being thrown around, the buying process can be bewildering. This page will help you to choose the best air conditioner for you.

If it's cleaner, rather than cooler, air you're after, head to our air purifier reviews.

What are the different types of air conditioner? 

Domestic air conditioners break down broadly into the following types:

Standalone air conditioners

Standalone air conditioners, aka single-unit air conditioners, portable air conditioners and monoblock air conditioners. You plug these into a mains socket and dangle the hose out of a window or door, as pictured above

Split-unit air conditioners

Split-unit air conditioners, aka fixed air conditioners. These have an indoor and outdoor unit. The indoor unit is fixed to the wall, and the outdoor unit is fixed to the wall or installed on the ground outside.

Standalone air conditioners: pros and cons

Typical prices: start from around £200

Pros of standalone air conditioners:

  • An effective way to cool your home without needing to install anything.
  • Can be unplugged and placed in storage when not in use.
  • You vent hot air out through a hose, so you can move the unit from room to room.
  • More expensive models can double as dehumidifiers, air purifiers or electric heaters.

Cons of standalone air conditioners

  • Venting the hose through an open window could pose a security risk if left unattended.
  • 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. 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: pros and cons

Typical prices: start from around £500, not including possible installation fees

Pros of split-unit air conditioners

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

Cons of split-unit air conditioners

  • Tend to be more expensive than standalone units.
  • Needs to be permanently mounted on an outside wall by a certified professional.

What size air conditioner do you 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.

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 very rough guide, multiply the dimensions (in feet) of the room by five. 

So for a room measuring 15x10x8 feet: 15 x 10 x 8 x 5 = an air conditioner of 6,000 BTUs.

If you're concerned about how much energy an air conditioner will use, look out for one with a good energy efficiency ratio (EER). This is the ratio between an air conditioner's BTU and its the power input (in watts). 

In general, the higher the EER rating the more efficient the air conditioner.

What extra features should I look out for? 

Dehumidifier mode

A few air conditioners double up as a dehumidifier. This could be useful if you want an appliance that's going to be useful across the year, not just in summer. You'll need to connect up a hose (often not supplied) to drain away the water. Buying an expensive air conditioner just for dehumidifier mode can work out to be more expensive, and less effective, than buying two separate appliances, though. If you're primarily after a dehumidifier, check out our dehumidifier reviews

Fan speeds

Having a range of fan speeds is useful, as it affects the rate at which your room cools down (and the noise the air conditioner makes). Two or three is a typical number of fan speeds. Many also have a fan only mode, which has no cooling effect – it just circulates the air within the room. 

Heat mode

This will allow you to use your air conditioner as an electric heater – particularly useful in winter. Although, just like with a dehumidifier, it could work out better value to buy them separately. Read our electric heater reviews to find the best.

Remote control

Allows you to adjust the settings without moving from your seat. Look for a machine with a dock to store the remote if you're prone to losing things. 

Sleep or night mode

This reduces noise by running the compressor and fan more slowly. Often the target temperature will increase automatically across the night so that you don't wake up freezing cold. No air conditioner will be silent, even on sleep mode, so manufacturers (even those offering a sleep mode) often recommend pre-cooling rooms before you go to bed, rather than attempting to sleep with an air conditioner running. 


These 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.

Setting up an air conditioner 

Here are a few pointers on getting your portable air conditioner set up correctly. 

  • You'll only be able to use a portable air conditioning unit if you have certain types of window, so definitely check this before buying. Generally, the window kits provided are only suitable for sliding or sash windows or doors. If you have a different type of window, you may still be able to use the air conditioner with the hose extended through an open window, but this will work less efficiently and use more energy (the better-sealed the room, the less hard the air conditioner has to work) and may not even be possible – for example, if your windows open from the top inwards, and your hose isn't long enough to reach it.
  • It's easier with two of you. Although technically 'portable', all of the models we tested were very heavy (up to 30kg) and awkward to lift out of the box. If you live alone, rope someone else into coming over to help you set it up, particularly if you're pregnant or elderly.
  • Don't expect to use it right away. Some need to be left to stand upright for as many as six hours before being used. Make sure to check the manual. 
  • Attaching the connectors to the hose takes patience. We had to grapple with all the models we tried, though some were worse than others. There's a knack to it, and you're likely to struggle unless you've had a similar appliance before.
  • Allow 50cm around the unit for air to circulate.
  • Never plug an air conditioner into an electrical outlet using an extension lead. Always plug it into the mains. 
  • Air conditioners often shouldn't be installed in laundry rooms, wet rooms or bathrooms. 
  • When setting up wi-fi on your air conditioner (if applicable), place the air conditioner as close to the router as possible. Manufacturers often state that the unit requires a good signal during the set-up process.  

First looks: air conditioner reviews 

We tried out three portable air conditioners from popular brands De'Longhi, ElectriQ and Meaco. For each air conditioner we assessed:

  • how quickly it cooled down a room
  • how easy it was to use, including assembly
  • how good the instruction manual was
  • how easily the filters could be removed and replaced
  • how truly 'portable' it was
  • how noisy it was. 

Our top pick air conditioner

None of the air conditioners we tried succeeded in reaching the temperature we selected on the thermostat, but all three reduced the temperature and left the room feeling cooler. While all three are heavy, bulky and fiddly to set up (in terms of attaching the hose to the connectors and the machine), our favourite model was the easiest to use of the three. 

Get our full first look verdict for each air conditioner, and find out which was our favourite, in the table below. Not yet a Which? member? Join Which? to access this and all of the reviews on our website. 

Air conditioners first looks
Name Price Features First Look verdict


De'Longhi PAC N90 DL portable aircon unit


The De'Longhi PAC N90 DL offers: cooling, a fan (three fan speeds in cooling mode and a fan-only mode), a timer, a thermostat, a remote control and wheels. 

The filters require cleaning once a week. 

Dimensions: 75cm x 45cm x 40cm (h x w x d)

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electriQ-12000-BTU-SMART TABLE

electriQ 12000 BTU smart portable air conditioner


The electriQ 12000 BTU smart portable air conditioner has the following features: cooling, a fan (three fan speeds in cooling mode), a timer, a thermostat, a heating mode, a sleep mode, a dehumidifier mode, a remote control and wheels. 

It also has a smart mode, making it controllable from your smartphone app (iOS or Android) via wi-fi. 

The air filters require cleaning every two-three weeks, depending on how often you use your air conditioner and the quality of the air. 

Dimensions: 72cm x 440cm x 335 cm (h x w x d)

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MeacoCool-MC-Series-9000BTU TABLE

MeacoCool MC 9000 portable air conditioner


There are two versions of this model - Cooling Only and Cooling and Heating. 

We tried out the Cooling Only Mode, which offers: cooling, a fan (two fan speeds in cooling mode and a fan-only mode), a thermostat, a timer, a sleep mode, a dehumidifier mode, a 'smart' (in effect, auto) mode, a remote control and wheels. 

The filters should be checked, to see if they need cleaning, on a weekly basis. 

Dimensions: 74cm x 32cm x 32cm (h x w x d)

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Maintaining your air conditioner 

Here's how to keep your portable air conditioner in peak condition for as long as possible:

  • 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 and fans regularly on both portable and split models. This will often involve vacuuming the filter or washing it in warm soapy water and cleaning the fan with a soft, dry cloth. However, this may vary from model to model – always follow the instruction manual. Before buying, check our first look table to find out whether you’ll be able to easily access these parts for cleaning.

If you want to find out the reasons for and against buying an air conditioner, and the alternative ways you can cool down your home, see should I buy an air conditioner?