How to buy the best air conditioner

The best air conditioners will cool any room quickly and evenly. However, poorer air conditioners make a racket, use more energy than others and leave warmer and colder patches. Pick the perfect one - if you truly need one - using our expert buying guide.

For most people in the UK, particularly those with small homes or with reduced strength to heave an air con unit about, an electric fan will be the most sensible buy. But if you're shopping for a room-cooling air conditioning unit, terms such as 'standalone', 'BTU' and 'refrigerant' can get confusing.

To help you shop savvy, we'll explain the difference between types of air conditioner, plus offer some tips on maintaining yours once it's set up. Once you know what you're looking for, head over to our air conditioner reviews and bag a Best Buy.

Types of portable air conditioners

If you own a chalet-style property, an attic conversion bedroom or a conservatory, an air conditioner could be a worthwhile investment.

There are two main types of domestic air conditioner, each offering their own unique set of features. At a glance, this is what differentiates them:

How much does an air conditioner cost?

At the time of writing, our cheapest air conditioner on test will set you back by around £300. But at the other end of the scale is a premium model that costs more than £700. Consider how much use you'll get from it as you might not want to spend hundreds of pounds if you're only going to roll it out of storage a couple of times a year.

How much energy do air conditioners use?

Our data shows that portable air conditioners use as much energy in one hour as a typical fridge freezer uses in one day. You might not leave them running all day, but the costs can easily rack up.

The energy efficiency of an air conditioner is usually measured by its energy efficiency ratio (EER). This is the ratio between the cooling capacity in British thermal units per hour (BTU) and the power input in watts. Generally, the higher the EER, the more energy efficient the air conditioner, although the actual BTU delivered by a machine can vary.

Best portable air conditioner

What is a portable air conditioner?

These are also known as single-unit, standalone and mono-block air conditioners. They usually have wheels on the bottom so you can roll them between rooms.

They are ideal for cooling a single room and they stand on the floor with the attached hose dangling out of a nearby window. If you can't install a permanent window air conditioner because of a lack of space or building restrictions, a portable model could be a sound investment.

How does a portable air conditioner work?

Portable models extract hot air from your home and push it outside through the attached hose. A reliable model will cool the room you're in, but don't expect it to push cold air down the hallway or into another room.

Due to condensation, water droplets are collected, so you'll need to manually remove the water from the tank every so often and clean the filter at the same time.

Are portable air conditioners worth the money?



Best split-unit air conditioner

What is a split-unit air conditioner?

Also known as fixed air conditioners, these are comprised of two parts: a condensing unit (mounted outside) and an evaporator (mounted inside). Both parts need to be connected, so installation is far more complex compared with a portable model.

These machines are quieter and more efficient than portable air conditioners, but need to be permanently positioned in just one room. If you've settled on a split-unit air conditioner, you'll probably need to get it set up by a professional – note that installers tend to be at their busiest during summer.

How does a split-unit air conditioner work?

They feature a compressor in its outdoor unit that circulates the refrigerant and turns it from a gas to a liquid.

That liquid passes through coolant lines to the indoor evaporator, where it transforms from a liquid to vapour. Heat is removed from the surrounding air and cooled air is blown into your home.

The outdoor unit will then turn the refrigerant vapour back into a liquid. This process will repeat over and over until the unit reaches the temperature you've programmed.

Are split-unit air conditioners worth the money?



Air conditioner features to look out for

Dehumidifier mode

Some models double up as a dehumidifier, meaning they serve a purpose throughout the year, not only in summer. If you're primarily after a dehumidifier, though, we recommend buying a dedicated dehumidifier instead.

How to buy the best air conditioner

With some air conditioner-come-dehumidifiers, you'll need to connect up a hose (which might not be supplied) to drain the water. With others, you'll need to set the machine up as you would in air conditioning mode, with the hose out of the open window.

Tempted by a dehumidifier? Before you hand over your money, check in with our reviews to ensure you're choosing wisely.

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). Most models have three fan speeds and some also have a fan-only mode, which has no cooling effect and simply circulates the air within the room.

We don't recommend buying an air conditioner primarily for the fan function – you can save significantly on floor space and money by buying a fan instead.

Remote control or smartphone control

Useful if you want to adjust the settings without moving from your seat. When we get our hands on an air conditioner with smart features, we run it through rigorous privacy and security tests.

Heating mode

Some air conditioners can be used as an electric heater, which could prove useful in winter.

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 you don't wake up freezing cold.

But no air conditioner is completely silent, even on sleep mode. In fact, you're better off pre-cooling your room before you go to bed, rather than attempting to sleep with an air conditioner running.


This allows 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 an air conditioner with a clock and 24-hour setting. Some only have countdown or delay timers that need to be reset daily.

What size air conditioner do I need?

They 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. Use this calculation to work out what BTU is right for you:

Multiply the dimensions (in feet) of the room by five. So for a room measuring 15ft x 10ft x 8ft you would calculate 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 a model with a good energy efficiency ratio (EER). This is the ratio between an air conditioner's BTU and its power input (in watts). Generally, the higher the EER rating, the more efficient it is.

You could also look at the claimed energy class. Air conditioner manufacturers are obliged to self-certify their energy class, from A to G. However, we conduct our own expert tests according to the European Standard BS EN 14511:2013. Often, we find the claimed and actual energy class to be different.

Where to buy air conditioners

When shopping online, make sure you’re dealing with a reputable seller. Before you part with your money, check the retailer's returns policy and have a look at some customer reviews. Demand for air conditioners is lower in winter, so you may be able to bag a bargain in an end-of-year sale.

Popular retailers that stock air conditioners include:

Find out which retailers are rated highly by Which? members with our guide on the best and worst shops.

Can you hire or rent an air conditioner?

Yes, there are lots of companies that offer this. Trying a portable model before you buy could save you from making a costly mistake. For instance, you may not realise how much noise these machines can make. At their quietest, they sound like a fridge on its cooling cycle, and some models will rattle and gurgle.

Rental prices typically start from about £60 per week for a compact, lower-powered model, all the way up to £200-plus for higher-powered units.

How to install an air conditioner

All of the models we've tested are heavy (up to 30kg) and awkward to lift out of the box. If you live alone, we suggest you get someone else to come over and help you set it up, particularly if you're pregnant or elderly.

Don't expect to use it right away as some models need to be left to stand upright for as long as six hours before being used – so check the manual.

Attaching the connectors to the hose takes patience. We've had to grapple with all the models we've tried, although 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.

Ideally, you need to allow 50cm around the unit for air to circulate. Never plug an air conditioner into an extension lead, either, always plug it directly into the mains socket.

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 setup process.

If you've purchased a split-unit air conditioner (as shown below), this will likely need to be installed by a professional.

Air conditioner window seal

Your portable air conditioner may come with a window sealing kit, but you'll only be able to use it if you have a certain type of window. Generally, the kits provided are only suitable for sliding, sash or French windows.

If you have a different type you should 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 the room is sealed, the less hard the air conditioner has to work.

How to maintain your air conditioner

To keep your portable air conditioner in peak condition, remove bungs to drain water from portable units at the end of summer, before they're 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.

You should clean the dust filters and fans regularly on both portable and split-unit models. This will often involve vacuuming the filter or washing it in warm soapy water and cleaning the fan with a soft, dry cloth.

Are air conditioners eco-friendly?

Portable air conditioners can use a lot of energy, especially if left running all day. Split-unit air conditioners tend to be more energy efficient, but these are more expensive and have to be permanently installed by a professional. We don't test split-unit air conditioners as they're less popular in the UK.

While the electricity used to power portable air conditioners can come from renewable energy sources, this can’t be guaranteed. Electricity is generated from a mixture of burning fossil fuels, renewables, gas and nuclear, but this is mixed up in the grid.

Portable air conditioners also use refrigerant gas to help cool your room. This can come in the form HFCs (hydrofluorocarbons), a greenhouse gas that when emitted can contribute to global warming. If yours is working properly, it shouldn’t release any HFCs. However, if the unit leaks or is disposed of incorrectly, that’s when harmful greenhouse gases can be released.

The UK is aiming to phase down the use of HFCs by 2030 by 79% for alternatives that have less of a global warming impact such as R290. You’ll find these are used more in the latest portable air conditioner models, however older machines may still use a HFC refrigerant.

Before you decide to invest in a portable unit there are some more sustainable options to cool your home that you can try beforehand, such as using an electric fan or closing curtains. However, if you do decide to use a portable air conditioner, there are some things you can do to make it more efficient:

How do I dispose of a portable air conditioner?

Around two million tonnes of electrical and electronic waste are generated every year, so it’s important to dispose of your portable air conditioner correctly and in a way that isn’t harmful to the environment.

If left in landfill, they can release the refrigerant into the environment. In some models these are HFCs, which are potent greenhouse gases.

Check with your local council to see if it offers household collection for yours. You can also see if your local recycling centre accepts them. In some cases you may have to pay a small fee for this.

Find out more about how to correctly recycle your electrical items.

What other options are there for cooling my home?

Air coolers

Air coolers look a bit like dehumidifiers and are generally pretty portable. They draw in warm air and cool it using water that's stored in a tank. Air coolers don't require installation and don't need to be vented through a window like portable units. They're much less effective than air conditioners, though.

Features to look out for:

Portable electric fans

Electric fans come in many shapes and sizes. They range from basic models right up to the expensive and multi-functional Dyson Hot & Cool, which doubles as an electric heater.

There are three main types. Desk fans, as their name suggests, are smaller fans designed to sit on a desk or table and cool you while you sit close by, while pedestal and tower fans are designed for a whole room.

Fans use just a fraction of the energy that air conditioners guzzle, as they only have to rotate lightweight blades. But while they may help your room feel less muggy, they only move the air around rather than actually cooling it.

Features to look out for:

Explore our tips on getting the most out of your electric fan.

Other ways to stay cool in the heat

There are a few useful things you can do to cool down in hot weather without having to invest in new equipment.

For starters, try closing the curtains when the sun is facing them. Closing curtains on an east-facing window before you go to bed can block the morning sun. For west-facing windows, you'll need to close your curtains in the late afternoon and early evening to block the sun.

Remember that opening the windows on either side of your home will allow air to flow through. If you have a conservatory, keep the door between it and your home closed, as a lot of heat may leak from the conservatory into other rooms.

Which? air conditioner reviews

We've tested portable air conditioners from a range of popular brands, including AEG, Argos own-brand Challenge, DeLonghi and ElectriQ.

For each air conditioner that reaches the Which? test lab, we assess a range of important factors, including how quickly the product can cool a room by 10°C, how easy it is to use (including assembly) and how straightforward it is to remove and replace the filters.

Ready to buy an air conditioner? Browse through our full selection of reviews and pick a model that's right for you.