Air conditioner reviews: FAQs

Who needs an air conditioner?

For some, keeping cool isn’t a luxury - it’s a necessity. Babies sleep better in rooms no warmer than 20°C. Older people are also at risk.

The body tries to cool itself by pumping blood to the surface of the skin. This puts excessive pressure on the heart as it has to work harder. As water is lost from the body in the form of sweat, the blood thickens. Thick blood clots easily. Older people tend to suffer from these problems without the heat, so their problems are compounded in the summer.

Do they work?

All the air conditioners we tested will cool you down

Air conditioners do cool you down. All the models we tested can lower the room temperature by several degrees, and are generally easy to set up and use. Our Best Buys do this the fastest and are the quietest models.

All models have a choice of settings for different conditions. On a cooler day, for example, you can use a fan-only setting to freshen your room. If the weather’s particularly sticky, you can take the moisture out by using the dehumidifier option.

So far, so good. But there are some downsides. The main annoyance is that they’re noisy and portable models take up quite a bit of space. Fixed, split models are quieter, but need to be permanently installed.

The machines' electricity consumption is gluttonous compared to other appliances. Only one model we tested meets its claimed A-rating for energy efficiency, with most others falling way short of the mark.

How do they work?

When switched on, air conditioners compress a refrigerant gas. It is then ran through a series of coils to cool and condenses into liquid. The liquid moves through an expansion valve, evaporating, to create a cool gas which absorbs the heat from a room, cooling the air.

This process also creates hot air, which you need to expel outside the room through a hose – either by passing the hose through a hole in an outside wall or an open window.

Are energy ratings meaningful?

Our tests show you should take energy-labelling claims with a large pinch of salt. While most units we tested claim to meet class A – the most energy efficient standard – only one met this level. One even missed its claimed class B, rating as class C in our tests.

At worst, one model rated as level F in our test. The classification system for air conditioning is quite flexible, allowing a 12-15 per cent margin of accuracy.

The portable air conditioners we’ve tested use as much energy per hour as a typical fridge freezer uses in one day. In their defence, you’ll probably only use them for a few hours each day.

Few air conditioners are as energy efficient as they state, so you’re best off ignoring these confusing claims when choosing which to buy. We calculate you could pay nearly £15 over an eight-week period if you used one every day for three hours - which will give you a better idea of energy efficiency.

Should I buy or rent?

The air conditioners we tested start at about £80 to buy. But if you want to try before you buy, or don’t have much storage space, you might consider renting.

Trying a portable out before you buy could save you a costly mistake. For instance, you may not realise how much noise a machine can make. All air conditioners at their quietist sound like a fridge on its cooling cycle. Some are really noisy, rattling and gurgling away.

But rental prices aren’t cheap. For units similar to those we’ve tested, you can expect to pay around £40 to £80 per week from specialist online companies.

Shop around if you do want to hire. Renting from generalist hire shops, such as HSS or Jewson, shoots costs up to £128 and £152 per week. So renting for even a fraction of the summer could cost as much as buying an air conditioner outright.

Alternative options:

Air coolers are greener but a nuisance to refill

Air coolers

Many portable units that you'll see in shops aren't air conditioning units at all, but air coolers.
These are much less effective than proper air conditioners and work by blowing air over water. As the water evaporates, heat is drawn out of the room.

There are two ways to understand this:
• It's a bit like why you feel cooler when air blows on sweat.
• If you remember your school physics, read up about latent heat of evaporation here.

These units are not as effective as proper air conditioning. However, they are kinder to the environment and cost much less to run. And they don't have a hose so they're easier to move around.

Electric fans

Fans use less power than air conditioners, but don't cool the air.

Fans use a fraction of the power of air conditioners as they only have to rotate three blades. But they only move the air around - they don’t cool it - and their motor will generate heat while they do this.

In this review

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