How to choose the best energy-efficient air-conditioner for your home

25 June 2021 | Celia Topping

Recent heatwaves have had us all reaching for fans, cool water sprays, cold flannels and iced drinks. Uncomfortably stuffy days and sweaty sleepless nights are no fun for anyone, especially if you’re working from home

You may feel like sticking your head in the fridge – but there could be a better way. Air-conditioning might not be the first solution you consider, because the UK’s climate doesn’t need it, surely? Plus they’re expensive and bad for the environment, right? But with increasingly sweltering summers, it might be time to switch your fan for something... well, cooler. 

What are the different types of air-conditioner? 

If you’re thinking noisy, bulky boxes fixed to the wall, think again. Modern fixed air-conditioners – also known as split-unit air-conditioners – are far more streamlined than in days gone by, and they’re quick to install.

Yet the Kings of Cool these days are small portable air-con units that you plug in, to make your room feel frosty as a fridge in no time. For everything you need to know about how to keep your cool when the temperature’s rising, read on:

Portable air-conditioners: pros and cons 

Portable air-conditioners (PACs) are also known as single-unit air-conditioners, standalone air-conditioners or mono block air-conditioners. These handy air-con units can simply be  plugged into a mains socket, and the hot air is fed out of the nearest window via a hose.  

Benefits of portable air-conditioners

  • With prices starting at £380, they’re a cheaper option than fixed air-conditioning
  • You can move them from room to room, making them the convenient choice
  • Can be unplugged and wheeled into storage once temperatures drop
  • Some models double as electric heaters, air purifiers or dehumidifiers, so it could be the unit you need for all seasons

Cons of portable air-conditioners

  • Although convenient, PACs don’t cool as efficiently as fixed air-con. Some hot air can escape into your room through the gap made by the hose being hung out of the window. Some units include a window sealing kit, but they’re not suitable for all windows. 
  • If you’re elderly or have reduced strength, PACs may not be the best choice, as they’re pretty heavy. Although they have castors and handles, they can be awkward to shift. You may need assistance.
  • There could be security issues if you leave the hose hanging outside while you’re not at home.
  • If you’re particularly house-proud, you may not want a white unit on wheels by the window, spoiling your feng shui! 

Fixed air-conditioners: pros and cons

The more traditional type of air-conditioner units are fixed to the wall. This appliance comes with 2 units – one fixed on the inside of an exterior wall, and the other fixed outside.   

Benefits of fixed air-conditioners

  • They’re more energy-efficient at cooling, and usually quieter than PACs
  • If you have one room that heats up specifically, fixed air-con is your friend
  • They’re a more secure way of cooling your home, as there’s no need to leave a window open 
  • They’re not exactly pretty, but they can be a little more discreet than a wheeled-out PAC
  • There’s no need to get them out and put them away as the weather changes

Cons of fixed air-conditioners

  • As you’d expect, a fixed air-con unit is more expensive than the standalone ones. Expect to pay upwards of £500, plus possible installation fees. 
  • As the name suggests, they’re fixed to your wall, so you can’t move them from room to room
  • You need an exterior wall to attach the air-con unit to, which can be an issue in some homes
  • Needs to be fixed by a certified professional

How much does air-conditioning cost in the UK?

You’re not going to pay less than £300 for a standalone unit, but you’d be advised to pay £500 or more for a decent one. Because of the high cost, it might be worth considering if you really need an air-con unit, or would a fan or air cooler suffice? More on that later… 

How to choose the best air-conditioner for your home

As with most appliances these days, there’s an abundance of products on the market – which can make the decision difficult. Here are a few tips on what to look out for when making your choice:

What size air-conditioner do you need? 

This comes down to the air-con unit’s British thermal unit (BTU) output. The higher the number, the more efficiently it can cool a room – with 5,000 to 8,000 BTUs being sufficient for most living spaces.

As a rough guide, you can use this calculation to work out how many BTUs you need: Dimensions of your room in feet x 5. So if your room is 15 x 10 x 8 feet, it’ll be 15 x 10 x 8 x 5 = 6,000 BTUs. 

One of the most common concerns about air-con is how much energy they use. You can check this via the A to G energy class ratings. But as these are self-certified by the manufacturers, it might be more precise to look at the energy efficiency ratio (EER). The higher the rating, the more energy-efficient the unit.  

Questions you need to ask when choosing a portable air-con unit

So you know what size machine you need – but what else do you need to find out about your air-conditioner before you buy? Here’s a list of useful questions you can ask, or find out online. 

  • How quickly can it cool a room by 10°C?
  • How energy-efficient is it? 
  • How easy is it to use, including assembly?
  • How simple is the instruction manual to understand ?
  • How easily can the filters be removed and replaced? 
  • How easy is it to move around?
  • How noisy is it?

What extra features should I look out for when buying a portable air-conditioner? 

Once you’ve got the basics down, it’s time to look at the bonus features that could be important to you. All portable air-con units come with certain features, while some come with additional extras. Here’s a guide to what you need, and what you probably don’t. 

Remote or smart control

Smart features can be pretty useful if you want to pre-cool a room before you get home. Just make sure the unit is compatible with your smart home platform. A remote control just means you don’t have to get up from your sofa if it’s starting to feel a bit stuffy. 

Fan speeds

Most models have 3 fan speeds, which affects the speed at which the unit cools your room. But bear in mind, the faster the fan, the louder the noise. Some models have a fan-only mode, but buying an air-con unit to use just as a fan wouldn’t make much financial sense! 

Sleep or night modes

This simply runs the fan more slowly, so it’s less noisy. No air-con unit is completely silent – so it’s a good idea to pre-cool your bedroom before you go to bed. If you want to leave the unit running, you may want to invest in earplugs. You can also set the temperature to rise throughout the night, so you don’t wake up shivering. 


If you know it’s going to be a hot day, you can set the timer to switch the unit on to cool your home before you get there – or switch it off while you sleep. 

Extra modes like dehumidifier or electric fan heater

Some air-con units have extra features, such as a heater – which is a great way of getting your money’s-worth through the year. But it could be worth checking out other standalone heaters, which may suit your needs better.

Another optional feature is a dehumidifier. But these may need a hose to drain away water, which a standalone dehumidifier doesn’t. So again, trying to get 2 appliances in 1 may not be the best solution.

Which air-conditioning units are the best?

Let’s look at the top 3 energy-efficient air-conditioning units around at the moment:

The quiet one

Even when the fan’s on high, the noise level is low, so you can rest and play with minimum disturbance. The super-quiet De'Longhi Pinguino PAC N90 has an A energy-efficiency rating, and can work as a dehumidifier, too. Around £550.

The super-chill one

Stand in front of the AEG ChillFlex Pro for long enough and you might get frostbite! With an energy-efficiency rating of A, this multi-functional unit automatically adjusts to the set temperature, and comes with a remote control and a 2 year guarantee. Around £560. 

The smart one

For super-connected smart home aficionados, add the electriQ AirFlex 14000 to your network of devices, to control your home’s cool factor from anywhere. It’s a powerful, ‘A’ energy-rated unit, with the capacity to cool rooms up to 400 square feet. Sync it with Alexa for a voice-activated chillzone. Around £550.

Setting up an air-conditioner

So you’ve brought your new frosty friend home and can’t wait to chill out with it. Here are a few tips on getting your portable air-conditioner set up correctly:

  1. “Portable” by name, but not necessarily by nature. Some of the units weigh up to 30kg, so ask a friend to help you get it out of the box, particularly if you’re elderly or pregnant. 
  2. Cooler climes await... but not straight away! Once the unit is out of its box, it’ll need to stand for a few hours before use. Your manual will let you know when you can switch it on for the first time. 
  3. The hose which vents the hot air away can be a bit of a struggle to attach. Read the instructions carefully and you’ll find there’s a knack to it. 
  4. The unit needs at least 50cm free space all around it, for the air to circulate properly. So don’t put anything on it, or stand anything too close to it. 
  5. Always plug your air-conditioning unit into the mains socket, not an extension lead. 
  6. Remember, electrical safety always comes first, so keep the unit away from water. Don’t use it in bathrooms, laundry rooms or other damp rooms. 
  7. If your new air-con unit is WiFi enabled, make sure you put it as close to the router as possible while you set it up, to get a good signal. 
  8. You need a suitable opening window to have a PAC, as the hose needs to dangle outside, to let out the hot air. Check before you buy. 
  9. If the unit comes with a window sealing kit, you can usually only use this with certain types of windows, such as sash windows or French doors. 

Maintaining your air-conditioner

Here’s how to keep your air-con unit in tip-top condition. 

  • If the summer has been super-humid, you may need to release the plugs to drain out the water every few weeks. And be sure to do it one last time before you pack it away for winter. 
  • Cleaning the dust filters and fans will extend the lifespan, but may involve vacuuming or washing it by hand in soapy water. Be sure to read the manual, to check what to do. 

What are the disadvantages of having an air-con unit? 

Air-con isn’t mainstream in the UK yet, for several reasons. Answers from a 2019 Which? Magazine survey explain why:

  • I don't need one in this climate (64%) 
  • It's bad for the environment (29%)
  • It's too expensive to buy/run (24%)

Other reasons include how obtrusive they are in the home, and the hassle of getting them in and out of storage. And concerns also covered the noise, and getting dry eyes from air-conditioned air. 

One solution to the “I don’t need one for this climate” naysayers, are rental options. Lots of companies rent out portable air-conditioners, and it could be just what you need to take the edge off a heatwave, without too much expense. Renting a PAC for a week costs £60 to £200, and gives you a chance to test any noise/space/convenience issues before buying one. 

How energy-efficient is an air-conditioning unit?

They differ from brand to brand, and model to model. But in general, they use about as much energy in an hour as your fridge-freezer uses in a day. Considering that chilling statistic, you probably won’t use the air-con for more than a few hours a day – and bear in mind it can get expensive during a heatwave.

Is air-conditioning bad for the environment

There’s no 2 ways about it – air-con units take a lot of electricity to run. That could be bad news for the environment if you’re not on a green tariff, like the 100% green electricity offered by OVO. Air-con units can also release harmful refrigerant gases into the atmosphere. So, even if you’re on a green tariff, make sure you get the most energy-efficient model, and be mindful about how much you leave it on. 

What other options are there for cooling my home?

If the price tag is a bit too hefty, there are other cheaper options, even if they’re slightly less effective:

Air cooler

These look similar but work differently, by drawing in warm air and cooling it internally with cold water stored in a tank. Air coolers don’t need an external hose, are portable, and cost in the region of £70 to £120. Things to think about include:

  • The size of tank – a larger tank means refilling less often
  • Whether it has a remote control – to set it from the sofa
  • Using ice packs – to increase the cooling capacity
  • Wheels and handles – to move it around easily to where you need it most

Electric fans

There’s a staggering amount of fans to choose from, in all sorts of shapes, sizes and prices. You can pay anywhere from £15 to £330 – and while they won’t cool the air, they will make it feel less humid – and they’re far more eco-friendly. Look for:

  • Speed settings – to control the strength of the air flow
  • Oscillation – this moves the fan from side to side, to spread the flow
  • Remote control  – to be in control from the other side of the room

Read our blog for more info on choosing the best energy-efficient fan for your  home. And head over to our handy guide, for tips on how to keep your home cool this summer

Choose OVO to power your home the green way

Choose OVO as your energy supplier and you’ll get:

  • 3-5% Interest Rewards when your account is in credit1 
  • A £50 gift card every time you introduce a friend

Check our range of plans, and see how much you could save.

Sources and references:

1. Interest Rewards are paid on positive balances of customers paying by monthly Direct Debit. It is calculated at 3% in your first year, 4% in your second year and 5% in your third year (and every year thereafter) if you pay by Direct Debit.