What is an Air Source Heat Pump?

An air source heat pump (ASHP) is an alternative way to heat your home and hot water which uses a renewable source of heat: the air outside. Like a fridge extracts heat from the air inside it, an air source heat pump extracts heat from the air outside for use in your home. It can do this at temperatures as low as -15° C.

ASHPs can heat water for your radiators and taps and are particularly effective with underfloor heating systems.

How do Air Source Heat Pumps Work?

The pump is installed outside your home. A fan inside the pump rotates to bring in air from the outside. The air is passed over an exchanger coil which contains a refrigerant fluid. The fluid boils and evaporates transforming into vapour. The vapour is then compressed at high temperature producing the heat needed for your home’s central heating and hot water supply.

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In April 2019 BBC Radio 4 discussed air source heat pumps including what an air source heat pump is, how it works and if it’s the right choice for UK homes. Click here to listen to the short but very helpful explanation between 11 minutes 37 seconds to 16 minutes 10 seconds.

Types of Air Source Heat Pumps

What is an air-to-air heat pump?

An air-to-air heat pump can heat your home by extracting heat from the outside air. Fans distribute this air around your home. An air-to-air pump will only heat your home i.e. it will not produce hot water but it can be used in reverse during summer as an air conditioning unit.

What is an air-to-water heat pump?

An air-to-water heat pump extracts heat from the outside air and uses it to heat your wet central heating system (radiators), underfloor heating and hot water cylinder for your taps etc.

Air-to-water heat pumps are most efficient when operating at a lower temperature for a longer period of time. The water produced will not be as high in temperature as it would with a traditional boiler. This is why it’s often recommended that ASHPs are installed alongside large radiators or underfloor heating systems so the heat is emitted via a larger surface area.

An air-to-water heat pump is eligible for the government’s Renewable Heat Incentive (RHI) scheme while an air-to-air pump is not. This means that you could receive a quarterly payment from the government for every unit of energy generated by your air-to-water pump.

Air Source Heat Pump Costs & Prices

How much does air source heat pump installation cost?

It usually costs between £4,000 – £11,000 to install an ASHP in a typical home. It’s a big investment, but there are some significant potential savings if you consider the long term.

Do you really save money with a heat pump?

Installing an air source heat pump can be a great way to reduce your energy bills, but this will depend on which type of heating system you are replacing.

Is a heat pump cheaper than gas?

The greatest energy savings are usually seen when an ASHP replaces an electric or coal heating system. If you have a boiler fueled by gas, an ASHP is unlikely to save you money. We’ve outlined some potential savings using figures produced by the Energy Saving Trust to give you an idea of how much a typical 4 bed detached home could save in energy costs.

Potential ASHP Energy Savings

Existing Heating System	Energy Savings Per Year?
Old G rated Gas Boiler	£400 – £465
New A rated Gas Boiler	Increase of £35 – £55
Old G rated Oil Boiler	£460 – £545
New A rated Oil Boiler	Increase of £45 – £55
Old Electric Storage Heaters	£800 – £900
New Electric Storage Heaters	£465 – £545
Coal	£425 – £525

The energy efficiency of an ASHP is far better than a standard boiler. Even the most efficient boilers waste between 6-12% of the energy they use while an ASHP doesn’t waste any. In fact, an ASHP produces 3 times as much energy as it uses.

ASHPs are run on electricity so it’s important to make sure you’re on the best energy tariff available. Take a look at our Energy Switching Guide for more information.

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Potential Carbon Savings

In addition to potentially reduced energy bills, ASHPs are a great way to lower your home’s impact on the environment.

Existing Heating System	Carbon Savings Per Year?
Old G rated Gas Boiler	3,300 – 3,900kg
New A rated Gas Boiler	1,200 – 1,400kg
Old G rated Oil Boiler	5,200 – 6,100kg
New A rated Oil Boiler	2,300 – 2,700kg
Old Electric Storage Heaters	4,600 – 5,700kg
New Electric Storage Heaters	3,200 – 3,800kg
Coal	6,900 – 8,300kg

Air Source Heat Pump RHI (Renewable Heat Incentive)

If you install an air-to-water heat pump into a wet system you could be entitled to earn money through the government’s RHI scheme. In an effort to encourage homeowners to adopt renewable heating solutions and reduce the UK’s carbon footprint, they are offering payments for energy generated through renewable solutions like solar and ASHPs. The payback you could receive is based on a per kWh tariff which is recalculated regularly. Payments are made quarterly over 7 years.

To give you an indication of the money you could earn through the ASHP RHI, we did some calculations with the government’s BEIS Domestic Calculator*.

Detached Home (3 beds)	RHI Payment per Quarter	Annual RHI Payment	Total RHI Earned Over 7 years
Replacing Gas or Oil System installed pre 2005	£213	£850	£5,950
Replacing Coal Fired System	£220	£880	£6,160
Replacing Other Electricity System	£183	£730	£5,110
Bungalow (2 or fewer bedrooms)	RHI Payment per Quarter	Annual RHI Payment	Total RHI Earned Over 7 years
Replacing Gas or Oil System installed pre 2005	£173	£690	£4,830
Replacing Coal Fired System	£170	£680	£4,760
Replacing Other Electricity System	£145	£580	£4,060

*Tariff of 10.49p / kWh (valid for applications received before 01 July 2018). Based on a home located in England or Wales, built between 1976 – 1982, unknown amount of loft insulation and cavity walls with insulation. The calculations are intended as a representation only.

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Review of Air Source Heat Pumps

Is an air source heat pump the right choice for your home? We’ve taken a look at the advantages, disadvantages, costs and potential savings to help you make the right choice.

Is ASHP installation difficult?

Air source heat pumps are easier to install than ground source heat pumps as you won’t need to dig up your garden. The main unit will be installed outside your home but will need to be incorporated into your existing system which can be difficult. They are often recommended for new builds or if you’re having other building work completed at the same time to reduce costs.

Are ASHPs carbon free?

An ASHP will produce far less carbon emissions than other heating systems but as it uses electricity to run it is not carbon free like a solar or wind powered system.

Will an ASHP produce enough heat for your home?

ASHPs work most efficiently at a lower temperature so the heat they produce may not be as high as a boiler can produce. This is why underfloor heating or larger radiators are recommended. You can also boost the temperature of your hot water with an immersion heater in the hot water cylinder. Effective insulation is also important to retain as much of the generated heat as possible.

Does a heat pump work in winter?

The energy efficiency of the pump will drop in winter but it will continue to extract heat in temperatures as low as -15°C, so it will heat your home and hot water all year round.

Are heat pumps noisy?

ASHPs have a reputation for being noisy. It’s true that there will be some noise as it works but modern pumps are far quieter than early versions. It’s advisable to install the pump as far away from your main living or sleeping rooms as possible to prevent this being an issue.

How long will a heat pump last?

With proper maintenance ASHPs can operate for as long as 20 years. They are also very easy to maintain with professional servicing every 3-5 years.

Advantages & Disadvantages of Air Source Heat Pumps

Potential Advantages	Potential Disadvantages
Save money through reduced energy bills	Retrofit installation can be difficult
Earn money through RHI scheme (air-to-water only)	Can be noisy
High energy efficiency	Can be more costly to run than A rated gas or oil boilers
Lower carbon emissions	May need to replace radiators with larger versions
Works all year round	Energy efficiency reduces in winter
Easy to maintain	Only effective in adequately insulated homes
Lasts up to 20 years	Hot water and radiators may not be as hot

Is a Heat Pump Right for Your Home?

We’ve taken you through how air source heat pumps work as well as the advantages they can bring but whether you should have one installed comes down to whether its the right choice for your home.

Air source heat pumps are best suited to off-grid, well-insulated properties or new-builds. For homes currently using A rated gas or oil boilers ASHPs are generally not recommended in terms of energy savings.

You don’t need planning permission in England and Scotland as long as the installation meets certain criteria. In Wales and Ireland planning permission is necessary.

The pump will need to be installed outside your home so you will need a suitable outside space which is clear of obstructions.

To get the full benefit of an ASHP you need large radiators or an underfloor heating system and, in the case of air-to-water pumps, a hot water cylinder.

A high level of insulation is needed to ensure your ASHP can heat your home effectively.

If you’re interested in finding out more about air source heat pumps we have some guides to help you. From the pros and cons to the best manufacturers, we can help you make that all important decision.