A guide to air source heat pumps: what are they and how do they work?

Update: The Government’s Heat and Building Strategy

We believe that air source heat pumps are important to the future of home heating, and we’re not alone. The Heat and Building Strategy - the first ever government strategy on decarbonising heat in homes - sets a new target for phasing out new gas boilers from 2035 in favour of low carbon heating systems like air source heat pumps. In this time the government will also be making air source heat pumps more affordable, with a £5k grant per household to help homeowners buy and install this carbon cutting tech!

Here’s the truth about home heating. Gas boilers might be more energy-efficient than they used to be – but these days, there’s a better way to run your central heating system. How? With an air source heat pump.

Air source heat pumps have moved the goalposts when it comes to heating your home. They’re super-low carbon and low maintenance – and they could also help to cut your home heating costs. But are they right for your home? Here’s everything you need to know.

Find out more about why we need to decarbonise home heating

What is an air source heat pump?

Air source heat pumps are a greener alternative to boiler heating systems. They’re low-maintenance and highly efficient – and they might just cut your heating costs. Win-win!

Air source heat pumps look a bit like air-conditioning units – and their size depends on how much heat they'll need to generate for your home. The bigger the heat pump,  the more heat is produced.

Air source heat pumps use one simple, renewable resource as their main source of energy – air. They take energy from the air outside (even when it’s cold) and convert it into heat for your home. Basically, they work just like fridges and air-conditioning units – just in reverse. 

What is a heat pump system?

In simple terms, a heat pump extracts heat energy from the air or ground – even when it’s cold outside – and uses it to warm your home. Amazing, huh?

The pump absorbs naturally-occurring heat from the air, earth, or water outside, and uses this to heat your home and give you hot water. Since it transfers heat, rather than generating it, heat pumps are one of the most efficient means of warming your house.

Learn more about how much energy you use to heat your home, and the costs involved, in our guide.

Types of air source heat pumps

There are 2 main types of air source heat pumps:

1. Air-to-water systems: these distribute heat by pumping liquid through pipes and radiators, or through underfloor heating pipes. This is the most common type, and it can be used for both heating and hot water.
2. Air-to-air systems: these produce warm air, which is circulated around your home by a network of fans.

How air source heat pumps work

Get your science hat on, and let’s look at the process in 4 easy steps:

1. The pump takes in air from outside to heat a liquid refrigerant. The heat turns the liquid into a gas through evaporation.
2. Using electricity, the pump compresses this gas, heating it up even more.
3. The gas condenses back into a liquid again, releasing its stored heat.
4. This heat is sent to your radiators, underfloor heating, and hot water cylinder. So you’ve got a cosy home and hot water stored, ready to be used for showers, baths, and taps.
5. Meanwhile, the liquid refrigerant cools off, getting ready to start the whole process again.

You’ll need to have a compressor unit fitted outside of your home as part of the installation. It’s useful to have a sunny spot for this, so the pump won’t have to work as hard. But an air source heat pump can even absorb heat from the air at sub-zero temperatures – so it’ll work even if you’ve only got a shady space. 

From storage heaters to heat pumps, find out about the world’s best low-carbon solutions to heat your home.

What are the pros and cons of an air source heat pump? 

Air source heat pumps are low maintenance, and generally more environmentally-friendly than the systems they replace. The main component used to create heat is air – a natural, renewable resource. But they’re not suitable for all types of home, so it’s good to be aware of the pros and cons:

Air source heat pump benefits:

• They could lower the costs of heating your home – especially if you’re switching from an electric, oil, LPG (liquefied petroleum gas), or coal-fuelled system.
• They produce far fewer carbon emissions than fossil fuel boilers.
• Because they use air – a renewable resource – they’ll help lower your carbon footprint. By how much depends on the fuel source they replace.
• They’re very efficient and run well without wasting much energy.
• They typically last longer than a boiler – about 20 years.
• Health: heat pumps don't emit any gases or particulates – unlike gas, oil, and lpg boilers, which can worsen air quality.
• Safety: heat pumps don't burn stuff – and that makes them inherently safer than boilers, which can leak gas, carbon monoxide, or even be a fire or explosion risk.

Air source heat pumps – disadvantages and things to consider:

• Air source heat pumps work best at lower heating temperatures – so they’re better if you have large radiators, or underfloor heating.
• Because they heat to a lower temperature than traditional systems, you’ll need good insulation and draught proofing, to help keep your home toasty warm.
• They only work with homes that have outside space – but bear in mind that they could free up space inside, as you’ll no longer need a boiler.
• Some (usually older) models can have rather noisy outdoor fans. But manufacturers are working on new ways to keep noise levels low. These days, many are actually whisper-quiet.
• They do use some electricity to run – so they’re not completely carbon neutral. But the environmental impact is pretty low, and getting lower as more renewables come onto the electricity grid

Air source heat pump costs

How much is an air source heat pump?

A typical air source heat pump usually costs between £4,000 and £9,000¹. That’s just the cost of the pump itself – remember, you’ll also need to budget for other parts of the system, such as radiators, underfloor heating, and controls. Plus, there’s the installation.

The final cost will vary, depending on the size of the heat pump and the complexity of the system you choose. It also very much depends whether you choose simple or advanced controls (for example, a weather-compensated thermostat). 

Cost of installing an air source heat pump

The total cost of getting an air source heat pump system, including installation costs, could be between £7,000 and £13,000, says the Energy Saving Trust². But the exact price (plus the running costs) will depend on the size of your home, the system you choose, and your insulation. 

Always make sure you get several quotes, and go with a trusted installer.

Running costs for an air source heat pump

The running costs will depend on:

• The size of your home – the bigger the space, the more power needed to heat it.
• How well insulated your home is. Better insulation means less heat loss.
• How warm you want your home to be. Higher temperatures take more energy.
• Whether you have underfloor heating or radiators. Typically the larger the “emitter”, the lower the flow temperature, and the more efficiently the heat pump can run.

Air source heat pump potential savings

Here’s a visual guide to how much you can save, compared to other popular heating options:

Can you really save money with a heat pump? Are they worth it?

Your potential savings will depend on what kind of fuel you’re replacing. If it’s gas, your gas use will go down, but your electricity use will go up. And because air source heat pumps are quite expensive to buy and set up, it could take a number of years to recoup the costs of installing one.

If, on the other hand, you have an electric, oil, LPG or coal system – particularly an old, inefficient one – an air source heat pump could work out cheaper.

If you’re building a new home, an air source heat pump could really be the best option. They’re quite simple to install – and you could even include underfloor heating or solar panels to help support the system, and make it easier for the pump to heat up your home.

Things to consider before installing an air source heat pump

Air source heat pumps work best with a well-insulated home – so here are some clever ways to boost your home insulation:

• Make sure your loft is well insulated
• Get cavity wall insulation wherever possible 
• Get draught excluders for outside doors, windows, and letterboxes
• Replace old windows with double glazing 

Other things to think about before you get an air source heat pump:

• You’ll need the unit to be installed outside your home, against a wall, with good airflow.

• How quickly you could make savings depends on the energy source you already use. If it’s coal or electricity, switching will be more efficient, saving you energy and money.

  

Financial help towards installing an air source heat pump

Your home might just qualify for help through the domestic Renewable Heat Incentive (RHI) scheme, in the form of a grant. This is due to end in March 2022, and is going to be replaced with the new Boiler Upgrade Scheme.

To help the UK reach its target of net zero emissions by 2050, the RHI scheme supports people who’ve installed renewable technologies in their homes. It gives quarterly payments for 7 years, which are designed to offset the cost of fitting and running your renewable heating system. 

To find out more about these schemes, get in touch with the Energy Saving Advice Service on 0300 123 1234 if you live in England or Wales, or Home Energy Scotland on 0808 808 2282 if you’re in Scotland. 

Air source heat pump energy labels 

Not all heat pumps are created equal – some are far more efficient than others. For that reason, the labels that are used to show the energy efficiency of domestic appliances like fridges, freezers, and washing machines will now also do the same for heat pumps. 

All new air source heat pumps are rated with this colour-coded system, which runs from dark green (which means most efficient) to red (which means least efficient). Here’s an idea of what they look like:

Photo credit: my-ecodesign.com

Most popular questions on air source heat pumps 

What are the differences between air source heat pumps and ground source heat pumps?

The clue’s in the name! Air source heat pumps work by absorbing heat from the air outside, using it to heat your home and give you hot water. Whereas ground source heat pumps absorb heat from the ground at low temperatures into a fluid (a mix of water and antifreeze). This happens inside a loop of pipe (called a ground loop), which is buried underground in your garden.

Ground source heat pumps require a lot more digging than their air source relatives. A typical 8kW output heat pump needs 200m of trench, with several loops – so overall you’d need 400sqm of space. Learn more about ground source heat pumps in our handy guide.

Are air source heat pumps classed as renewable energy?

Definitely! Because the main component used to create heat is air – a natural, renewable resource! This means air source heat pumps are generally more environmentally-friendly than the system they’re replacing. Especially if it’s a conventional or older system.

Can air source heat pumps work with radiators?

Yes, you can use radiators with a heat pump. But because of their low flow temperatures, radiators need to be bigger than for boiler-operated heating. This means that some existing radiators may need to be replaced.

Can air source heat pumps work with solar panels?

Indeed they can. Solar panels and heat pumps can work very well together, and will lower your overall electricity costs. And of course, if your solar panel can’t meet your energy needs, you can still use extra energy from the grid. There’s one note of caution: solar PV panels produce less electricity at the time of year when you need more heating and hot water – namely, winter.

Can air source heat pumps be indoors?

An air source heat pump works by transferring heat absorbed from the outside air to an indoor space. Which means you can’t generally install one inside a house, it’s best located on the ground outside.

Will an air source heat pump fit in the boiler cupboard?

Unfortunately not. Putting an air source heat pump anywhere indoors wouldn’t be a very efficient way to heat your home. An air source heat pump must be placed outside but the hot water cylinder may be able to fit in the boiler cupboard.

In summary: are air source heat pumps right for you?

If you’re looking for a low-carbon way to heat your home, an air source heat pump could be the ideal solution. But installing an air source heat pump is a big decision. You need to weigh up whether the cost to install is offset by the lower running costs and carbon savings

You also need to consider the type of home you have. Air source heat pumps are best suited to well-insulated modern homes. And they also work particularly well alongside technologies like underfloor heating. But they’re also effective in older homes, as part of a hybrid heat pump. This is where you combine a traditional boiler with the renewable energy of an air source heat pump. A hybrid heat pump system automatically switches between the 2, to give you the best possible energy efficiency.

Other ways to cut energy costs

Installing an air source heat pump can make a big difference to your carbon footprint – but they can be expensive. So you might want to find other ways to save on your energy bills. 

To start with, make sure your home and all your electrical appliances are working as efficiently as possible. Here are a few more bright ideas:

• Turn appliances off at the wall – don’t leave them on standby
• Use energy-saving light bulbs and other energy-saving devices
• Insulate your hot water tank – you could save around £35 a year
• When using your washing machine, set it at 30˚and pop it on a low spin cycle

Check out our handy tips on how to be more efficient with your heating and hot water. Learn more about the cheapest and most efficient way to heat your home. And discover 120 clever ways to save and conserve energy at home and on the go.

It also makes sense to consider switching energy suppliers. No matter which energy company you’re currently with, it’s always worth checking the market regularly, to see if you could save money by switching.

Switch to OVO, for cleaner, greener energy

Find out how much you could save today, and see how your current supplier matches up, next to our range of energy plans.

If you've got more questions about heat pumps, why not head to the OVO Forum? The Forum is where our green community comes together to share their firsthand experiences of green living, and to help each other out. There are tonnes of discussions about every aspect of heat pumps, so why not get involved and join the conversation?

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^{Sources and references:}

^{1 https://www.boilerguide.co.uk/air-source/air-source-heat-pump-costs-prices} 

^{2 https://energysavingtrust.org.uk/advice/air-source-heat-pumps/}