December 2023. Air source heat pumps, explained

How do air source heat pumps actually work? Are they the right choice for every home? And how can they help the UK reach its Net Zero targets? Scroll down for all the answers.

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What is an air source heat pump?  

This is what an air source heat pump looks like.

Air source heat pumps are an amazing new type of low-carbon heating. They take warmth from the air outside – and use it to supply your home’s heating and hot water, even when temperatures get as low as -15C.

Installed in a well-insulated home, heat pumps are just as cosy, cost-effective and convenient as gas boilers. But heat pumps run on electricity not gas – and they’re a lower-carbon way of heating your home.

That’s good news for your carbon footprint – and for the UK’s progress to Net Zero.


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Did you know?

Government green grants are making heat pumps more affordable than ever.

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England & Wales

from £499

With £7,500 government Boiler Upgrade Scheme grant.


from £499

With the £7,500 government Home Energy Scotland Grant.

How do air source heat pumps work?

Air source heat pumps use the same kind of technology that keeps a fridge or freezer cool – but in reverse.

The pump pulls in air from outside, then uses it to heat a special refrigerant liquid. As it warms up, the liquid turns into gas.

The warmth is compressed to increase its temperature – and provide lots of lovely heat for your home.

Once the gas has transferred its heat, it cools down, becomes liquid again. And returns to the start of the cycle.

The whole process only uses electricity and has an energy efficiency of over 350% – compared to an A-rated gas boiler, which is about 90% efficient.

The science behind heat pumps sounds amazing, but it’s not new. It was first described by scientist Lord Kelvin back in 1852.


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The pros and cons of air source heat pumps

British Gas are installing air source heat pumps.

What's great:

  • Much better for the environment – cutting your home’s CO2 emissions and improving local air quality
  • Government grants of £7,500 for homeowners in England, Wales and Scotland
  • Even more affordable with British Gas – choose from payment options like 0% interest over 2 years
  • Some models can be used with solar panels for a more self-sufficient system

What can be a challenge:

  • Heat pumps can be more expensive to buy than gas boilers, although government support is available
  • Some properties won’t have the right space, access or surroundings to install a heat pump – but your free British Gas home survey will tell you if your home is suitable, or if there are any changes to your home you should consider
  • To get the best efficiency from heat pumps, your home will need to retain a lot of its heat through good insulation
  • Installing a heat pump might involve the cost and disruption of making changes to your house – including bigger central heating pipes and radiators

Want to know if a heat pump is the right choice for your home?

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Our Warm Home Promise takes the worry out of switching to a heat pump

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We’ll only fit a heat pump if we’re 100% sure it’ll heat your home as well as a traditional boiler

If things aren’t cosy, we’ll put things right free of charge – or your money back.

What are the different types of heat pump?

Air source heat pumps use air and electricity to extract heat.

There are two main types of heat pump. They work in a similar way but extract their heat from a different source. It’s worth doing a bit of research before deciding which is best for you, but here are the main differences to think about.

Air source heat pumps

Heat is taken from the air outside using an external heat pump unit. This is transferred into your home to provide your heating.

  • Cheaper and easier to install than ground source heat pumps
  • Higher running costs than a ground source heat pump
  • The external heat pump unit is relatively small (about the size of two washing machines)
  • Can work in temperatures as low as -15°C
  • Don’t usually require planning permission
  • Last for around 20 years

Ground source heat pumps

Heat is taken from the ground using water circulating in underground pipes – and is then used to provide your home’s heating.

  • More expensive and trickier to install than air source heat pumps
  • Lower running costs than an air source heat pump
  • Need to dig up large outdoor area (e.g. garden) to lay pipework
  • More efficient in lower temperatures
  • Last for around 20 years

The other type you’ll sometimes hear about are hybrid heat pumps. These are air source or ground source heat pumps, but with a backup gas boiler that kicks in when extra heat is needed.

Whichever type you go for, you’ll be heating your home more sustainably than with a traditional gas boiler. In fact, if your electricity is zero carbon, you’ll be heating your home without creating any CO2 emissions at all.


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What government grants are available?

Replacing the nation’s gas boilers with greener, cleaner alternatives is a big part of the UK’s plans to reach Net Zero by 2050.

That’s why the UK authorities are offering financial incentives for people who make the switch to sustainable heating now.

England and Wales

The Boiler Upgrade Scheme was introduced in April 2022 (replacing previous schemes called the Renewable Heating Incentive and the Clean Heat Grant).

The scheme gives homeowners in England and Wales £7,500 to help with the initial cost of upgrading from a fossil fuel boiler to a low-carbon alternative, like an air source heat pump.


Homeowners in Scotland can apply for a £7,500 grant from Home Energy Scotland – with an extra £1,500 available for people living in rural areas.


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Why get a heat pump from British Gas?

Expertise and support you can rely on

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We offer a free home survey with one of our experts, plus industry-leading aftercare

We're confident we are the best choice for your heat pump installation.

Is a heat pump right for you?

Here are some of the key things to think about before deciding to get an air source heat pump installed.

  • Is your current heating system getting old? If it’s becoming unreliable or needs regular repairs, it’s probably time to replace it – and that could be the perfect time to invest in a heat pump.
  • Do you have the exterior space next to your home that can easily fit a heat pump unit? 1
  • Is your home properly insulated to make the most of the heat pump – or is that something you’d consider investing in?

If the answer to these is yes, an air source heat pump could be an excellent low-carbon heating choice for your home.

Want to speak to one of our experts about getting a heat pump?

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Ten heat pump myths, busted

There’s a lot in the news right now about heat pumps – and for good reason.

Their ability to heat your home without gas or oil means they’re a big part of the government’s Net Zero strategy. But with so many different opinions on exactly how they work and whether or not they’re worth the investment, it’s tricky to know what’s what.

But fear not. We’ve debunked some of the biggest heat pump myths out there to help you decide whether you’re ready to make the switch. It may well be easier than you think…

Heat pump myths

Myth #1: They don’t work in cold weather

This is one of the most common myths out there when it comes to heat pumps, and it’s simply not true.

Even when we’re wrapping up warm in the winter months, there’s still enough heat in the air and ground for heat pumps to absorb. In fact, the refrigerant in the heat pump can absorb heat in temperatures as low as -15°C. And because they compress the heat to a much higher temperature, it’ll still keep your home feeling cosy, no problem.

In the UK, it’s highly unlikely you’ll get temperatures that are too low for an air source heat pump. But for those who live in really cold countries, a ground source heat pump may be best, since they’re more efficient in freezing temperatures. That’s because the ground doesn’t really fall below 10°C, even in the harshest winters.

It might surprise you to learn that Sweden, with its frigid winters, is actually one of the biggest adopters of heat pumps in Europe.

Myth #2: Heat pumps are very noisy

Heat pumps often get a bad rep for being noisy. And while they’re by no means silent, if they’re installed properly and in the right place, they actually generate less noise than you might think. Air source heat pumps emit 50-60 decibels 2, which is only slightly higher than a low library whisper. Ground source heat pumps are even quieter as there’s no fan to worry about. And newer models are getting quieter and quieter, with thicker chassis and better fans.

If a heat pump does start making loud noises, it’s usually a sign that there’s something wrong.

Myth #3: Heat pumps always require planning permission

In most cases, you don’t need planning permission to install a heat pump as they fall under Permitted Development – but the requirements for this vary from country to country so it’s always important to check.

In the rare instance that they do need planning permission, it’s usually down to noise levels carrying across to neighbouring properties. That’s why it’s so important to get it installed by an expert. They’ll make sure it’s in the best place possible – i.e. away from any boundaries, to reduce the need for planning permission.

Myth #4: Heat pumps aren’t green because they use electricity

Many people think that because heat pumps use electricity, they can’t be green. But while heat pumps do need a small amount of electricity to get going, they’re much more efficient than traditional boilers, with the ability to generate 3.5kWh in heat for every 1kWh of electricity used. Plus, there’s no polluting gas or oil to worry about either.

Myth #5: They need a lot of maintenance

Once they’re all set up, heat pumps actually require very little maintenance – often far less than a traditional heating system. Depending on the model, they should last at least 20 years 3, and there’s usually no need for replacement parts during their lifetime. A quick annual service should keep it working happily for many years to come.

And for extra reassurance, British Gas heat pumps come with a 5-year warranty and central heating cover for the first year.

Myth #6: They’re just too expensive

We’ll admit, heat pumps are pricier to buy and install than your standard boiler. But with a longer lifespan and less need for expensive repairs, they can actually work out more cost-effective over the years.

Plus, government grants of £7,500 for homeowners in England, Wales and Scotland are available to help people switch from fossil fuel boilers to more sustainable alternatives. And if you buy from us, you’ll get 2 years’ interest-free credit to help make things more affordable too.

Myth #7: You need a huge garden for a heat pump

Air source heat pumps need much less outside space than ground source heat pumps. For a ground source heat pump, you need a garden (or another outside area) that’s roughly twice the footprint of your property.

But an air source heat pump is much more compact. If you have enough outside space for two washing machines side by side, there’s room for an air source heat pump. A huge garden really isn’t necessary.

Most people won’t need planning permission for an air source heat pump (unless you live in a conservation area, for example). But planning departments do have some rules to be aware of.

In England and Scotland, an air source heat pump needs to be at least one metre away from a boundary. And in Wales, it needs to be at least three metres away.

Myth #8: Heat pumps only work in new builds

Since you will need a fairly well-insulated home for a heat pump to work properly, you could be forgiven for thinking they’re only for newer, more energy-efficient properties. But the good news is that heat pumps can work in the vast majority of British homes – even those that suffer a bit of heat loss in the colder months.

Of course, if you live in an older, draughtier house, you’ll need to get it properly insulated before you think about getting a heat pump, including loft and cavity wall insulation and double-glazing. But for most of us, this won’t take too much work – and it’ll significantly increase your home’s efficiency and drastically lower your heating bills to boot.

Myth #9: They only work with underfloor heating

Heat pumps are ideal for underfloor heating systems, but they work really well with radiators too.

Since they function best at a slightly lower temperature than traditional boilers, you may need to install a couple more radiators or replace them with slightly bigger ones to really reap the benefits.

But every home and heat pump is different, so our expert engineer will help you decide exactly what you need. And if your home’s already well insulated, you may not need to make any changes at all.

Myth #10: Everyone needs to get a heat pump

You might have seen news stories that gas boilers are going to be banned and will be replaced by heat pumps. Well, it's not quite like that – as this article explains. Yes, there's definitely a need to change the way we heat our homes – but heat pumps are only part of the long-term solution. Heat pumps are great for well insulated houses, but not all the UK's homes are suitable for this tech.

Another heating system that’s being looked at is the hyrdogen boiler but it’s far from confirmed that this is the next step for the UK’s heating. And any switch to hydrogen is unlikely to happen until the mid-2040s, so there’ll be plenty of time for everyone to get ready for the change. The government is currently setting up trials of using hydrogen for domestic heating and cooking to see if it’s a feasible alternative to gas.

If the government does decide go ahead with switching to hydrogen, the first phase will introduce a 20% hydrogen blend into the UK’s mains gas supply – and the vast majority of boilers sold by British Gas today are hydrogen-blend ready. So if you do decide to buy one, you don’t need to worry about replacing it if and when the switch comes.

Pumped about heat pumps?

British Gas is installing air source heat pumps in more and more areas of the UK. Here’s what you’ll get with us:

  • Expert engineer installation
  • Help with claiming government incentives
  • Five-year warranty
  • Easy ways to pay, including interest-free credit.

Ready to make the transition to low-carbon heating? Find out more about getting your own heat pump by visiting our main page.


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Additional information

  1. Minimum space needed: Up to H: 1,565mm W: 1,100mm D: 450mm plus clearance around the pump.

  2. Source: Air-to-water heat pump system aroTHERM plus | Vaillant

  3. Source: Air source heat pumps | Centre for Sustainable Energy (