Air Source Heat Pump Installation

By 16 min read

Once installed, an air source heat pump acts like a boiler

Air source heat pumps can save you loads on your energy bills

 The Government gives you money for generating energy with a heat pump

Air source heat pumps are an alternative way to heat your home. They absorb heat from the outside air and increase it to a higher temperature to warm your property.

The pump runs on electricity, but it generates two to four times more heat than the electrical energy it uses. This means air source heat pumps are very energy efficient.

air source heat pump installation

What’s in This Guide to Air Source Heat Pump Installation?

Head straight to a specific section by clicking the links below.

How Does an Air Source Heat Pump Work?

You have a heat pump in your home already: your fridge. Your fridge works by transferring heat that’s inside it to the outside, to keep itself cool (if you hang around the back of your fridge, you’ll notice it’s warm). An air source heat pump does something similar in reverse: it takes heat from outside your home and brings it inside.

Here’s how it works: a fan draws heat from the air into the pump and uses it to warm up a liquid called a refrigerant. This liquid has quite a low boiling point, so it will turn into gas. The pump then compresses the gas, which increases its temperature, and pumps it into your central heating system, where it transfers its heat to your radiators or underfloor heating (and hot water tank, if you have one).

Did You Know?

An air source heat pump can cost anywhere between £5,000 and £11,000.

As the gas loses its heat, it turns back into a liquid again and flows back to the pump to start the cycle again.

Air at any temperature above 0°C always contains some heat, and an air source heat pump is able to extract heat from the air at any temperature down to about -15°C. However, the bigger the difference between the outside temperature and the temperature at which you want to heat your home, the harder your heat pump will have to work (and the less efficient it will become).

Air source heat pumps are most efficient when the outside temperature is about 7°C and you only ask it to heat your home’s central heating system to around 35 to 40°C.

Types of Air Source Heat Pump

There are 2 main types of air source heating systems: air to water and air to air.

  • Air to water heat pumps take heat from the outside air and use it to heat the water in your central heating system and hot water tank. As the heat produced by the pump is typically cooler than that produced by a boiler, you might need to install large radiators or underfloor heating. Air to water heat pumps are the more popular kind.
  • Air to air heat pumps take heat from the outside air and circulate it around your home through fans on the wall or ceiling. Their big advantage is they can heat a room very quickly – faster than radiators, in fact. In the summer they can also provide air conditioning. However, unlike an air to water pump, they can’t produce hot water.

Air Source Heat Pump Advantages

Efficiency: because they usually produce 2 to 4 times more heat than the electricity they use to generate that heat, air source heat pumps can mean a big reduction in your energy bills and a lower carbon footprint.

Easy to install: the installation of an air source heat pump isn’t complicated and you can choose where to put it outside your home. Other than flats, most homes should be able to accommodate an air source heat pump. Installation often takes no more than 2 days.

No need to store fuel: with an oil-fired boiler, for example, you have to have the oil delivered to your home and stored in a large tank so it doesn’t run out. With an air source heat pump, however, you have a constant supply of air outside and electricity from the mains.

Low maintenance: once it’s been set up, your air source heat pump will work automatically; there’s no need for you to fiddle around with controls. Air source heat pumps also have few moving parts, so there’s little chance of anything breaking.

Long lifespan: you can expect your heat pump to last for up to 20 years.

Precision: the heat pump will be controlled by a thermostat and timers, so you can set the temperature you want your home to be and when you want your heating to come on.

Air Source Heat Pump Disadvantages

Ice ice baby: ice can form on the pump when the outside temperature is below 7ºC, which will restrict the flow of air. The heat pump will then temporarily stop working while it defrosts – or worse, it might even start to work in reverse and take heat from inside your home to defrost itself. However, this should only be a problem in the colder winter months.

The unit will take up space in your garden: air source heat pumps are installed outdoors at the side or back of your home and are normally about the size of an air conditioning unit.

Potential environmental damage: the refrigerant gas in an air source heat pump can be made of hydrofluorocarbons (greenhouse gases) which, if they leak, are 1,600 times more damaging to the environment than carbon dioxide. Ask what refrigerant the pump you are thinking of buying uses; hydrocarbon refrigerants like R290 or R600a (propane and isobutane) will cause the least damage if they leak.

Your home will take longer to warm up: whereas a boiler can warm your home in as little as half an hour, a heat pump may take several hours, and during the winter, it may need to be on constantly to heat your home efficiently.

In a power cut, you’ll have no heating: unless you have a backup source of heat such as a boiler (which is advisable anyway), you’ll have no central heating when electricity goes down.


  • Efficiency
  • Easy to install
  • No need to store fuel
  • Low maintenance
  • Long lifespan
  • Precision

X Cons:

  • Ice can form on the pump
  • It'll take up space in your garden
  • Potential environmental damage
  • Your home will take longer to warm up
  • In a power cut, you’ll have no heating

Air Source Heat Pump Cost

Air source heat pump prices vary a lot: they can cost anywhere between £5,000 and £11,000. The Energy Saving Trust says a typical system should cost around £6,000 to £8,000, but air to air heat pumps often cost less than air to water heat pumps.

You may also need to make some changes to your central heating system which will add to the overall air source heat pump installation cost. Because air source heat pumps generate heat at a lower temperature than boilers, you’ll probably need to upgrade your existing radiators to larger ones. Each radiator is likely to cost between £200 and £300. If you decide to install underfloor heating as well, this can cost around £2,000 to £3,000, depending on the size of your home.

To get an accurate estimate of how much an air source heating system will cost you, you’ll need an installer to visit your home to do a survey, assess whether your home is suitable for a heat pump and put a quote together. Installers will often do this for free. To get a quote from a trusted installer in your area, just fill in the short form at the top of the page.

How Much Can an Air Source Heat Pump Save You?

An air source heating system can reduce your energy bills considerably if you currently have an old or inefficient boiler. Gas is usually around 3 times cheaper than electricity, however, so switching to an air source heat pump that uses electricity if you already have a decent gas boiler won’t make financial sense.

It costs around £750 per year to run a pump for a 3-bedroom semi-detached house, and £975 per year for a 4-bedroom detached house. The Energy Saving Trust estimates these annual savings from an air source heat pump for a 4-bedroom detached house in England, Scotland and Wales:

Current Heating System
Annual Energy Bill Savings with a New Air Source Heat Pump
G-rated gas boiler
+£400 to £465
A-rated gas boiler
-£35 to £55
Old electric storage heaters
+£800 to £990
New electric storage heaters
+£465 to £545
G-rated oil boiler
+£460 to £545
A-rated oil boiler
-£45 to £55
G-rated LPG boiler
+£1,145 to £1,350
A-rated LPG boiler
+£380 to £450
+£425 to £525

The figures for Northern Ireland are slightly different:

Current Heating System
Annual Energy Bill Savings with a New Air Source Heat Pump
G-rated gas boiler
+£440 to £520
A-rated gas boiler
-£45 to £55
Old electric storage heaters
+£555 to £705
New electric storage heaters
+£260 to £310
G-rated oil boiler
+£420 to £495
A-rated oil boiler
-£70 to £80
G-rated LPG boiler
+£1,845 to £2,175
A-rated LPG boiler
+£810 to £950
+£240 to £305

What Sizes Do Air Source Heat Pumps Come In?

The size of an air source heat pump is measured in kilowatts (kW). The more kW the pump generates, the more heat you will get. Air source heat pumps can be anywhere between 2.5kW and 18kW in size, but a 5kW to 12kW pump should cover the heating demands of most households.

The better insulated your home, the smaller pump you’ll need. You may also need a less powerful heat pump if you are using it alongside other heating systems, such as a boiler.

As a guide, you’ll probably need 1kW of power for every 10 square metres of property. The table below shows you what size air source heat pump* is suitable for what size home, depending on its square meterage and the year it was built:

House Build Year
2010 to present
up to 65m²
up to 100m²
up to 185m²
up to 200m²
2006 to 2010
up to 50m²
up to 90m²
up to 135m²
up to 155m²
1995 to 2005
up to 55m²
up to 85m²
up to 100m²
1975 to 1995
up to 70m²
up to 80m²

*These figures are just for central heating and do not include hot water.

It’s very important to get the right sized pump

A pump that’s too big will not only mean that you’ve paid more for a system that’s not the right size, but it will constantly chuck out more heat than you need and could end up short-cycling – switching on and off too quickly. This causes wear and tear on the system and shortens its life. It will also be expensive, as the pump uses most power when it starts up and may lead to your home being unevenly heated.

The problem with a pump that’s too small is simple: you’ll be cold as it won’t heat your property sufficiently. The pump will also be straining with the effort of trying to heat your home, so your bills will go up (as it’ll use more electricity).

An air source heat pump installer will be able to recommend the right sized pump for your property based on an assessment of: your home’s heat demand (how much heat and hot water you need), how quickly your home loses heat, how the heat pump will work alongside your current heating system, and how often you’ll need to use your heat pump.

Air Source Heat Pump Efficiency

The coefficient of performance measures how efficient an air source heat pump is. It is the ratio of heat output over electrical input: the amount of heat energy the pump delivers for every kilowatt (kW) of electricity it takes in.

For most air source heat pumps, the coefficient of performance will be between 2 and 4, so you’re getting 2kW to 4kW of heat energy out for every kilowatt of electricity used to generate it. You’ll know how efficient your air source heat pump is as it’ll come with a label from dark green (most efficient) to red (least efficient).

A word of caution: the coefficient of performance tells you the pump’s maximum efficiency. It’s usually measured at 7ºC, where the pump performs at its best. The seasonal coefficient of performance or seasonal performance factor is a better measure, as it gives an average efficiency over a range of temperatures (when the heat pump won’t be working at its best).

Do You Need Planning Permission?

In Wales and Northern Ireland: yes.

In England and Scotland: probably not, although there are still certain rules you need to follow, including the size of the heat pump, its location on your property and its visibility from the main road. It’s worth finding out from your local district or borough council what the exact conditions are before you get your heat pump installed, so you don’t break any rules.

When installing an air source heat pump, you should also get permission from your Distribution Network Operator (DNO). This isn’t your energy supplier, but it’s the company that operates the network that delivers energy to your home from the National Grid.

Good to know: if you live in a conservation area or World Heritage Site, the rules governing the installation of air source heat pumps will be stricter. If you live in a listed property, you’ll definitely need planning permission for a heat pump.

Choosing an Installer

Your air source heat pump and your installer will both need to be certified by the Microgeneration Certification Scheme (MCS) to ensure they meet industry standards. A credible installer should only recommend MCS approved products.

They should also be a member of either the Renewable Energy Consumer Code (RECC) or the Home Insulation and Energy Systems Contractors Scheme (HIES). They may also be a member of the Institute of Domestic Heating and Environmental Engineers, which is another professional body, or the Heat Pump Association.

Your installer should always provide a breakdown of your quote and confirmation of the work they’ll be doing in writing. You should also ask them for references so you can talk to previous customers about their experiences.

To get a quote for an air source heat pump for your home, just fill in the form at the top of the page with some basic information about yourself and your home, and we’ll put you in contact with an MCS accredited installer in your area.

Air Source Heat Pump Servicing

Air source heat pumps do require some maintenance, but more to make sure the pump is working properly and efficiently, than for safety reasons.

You should do your own regular checks to make sure nothing is obstructing the pump and the central heating pressure gauge in your house is properly set. You should clean and change the filters as necessary, keep the pump free from leaves and dust, clean the air grilles on the indoor unit and clean the fan blades (with the power off, obviously).

You should also have your air source heat pump serviced by an accredited engineer in line with your manufacturer’s and installer’s recommendations. This may need to be every year and it’s important because:

  • It will help your system to perform at its best and prolong its life
  • It may save you money on repairs and poor performance by detecting faults early, especially if the engineer finds a faulty part that is still under warranty
  • Most manufacturers’ warranties are only valid if your heat pump is regularly serviced
  • It reduces the likelihood of breakdowns
  • It might be a requirement of your home insurance

Your engineer should give you an annual service certificate when the service is complete. An air source heat pump service can cost anywhere from £90 up to £200.

Air Source Heat Pump Grants

A Government grant is available for air source heat pumps. The Renewable Heat Incentive (RHI) is a Government scheme to help people with the cost of installing renewable sources of heat in their homes, including air source heat pumps. It runs in England, Scotland and Wales, but not in Northern Ireland or the Channel Islands.

Under the RHI, you are paid for every kilowatt hour (kWh) of renewable heat you produce. The idea is that you recoup some of the upfront cost of installing a heat pump. For pumps installed between now and October 1st 2018, the rate is 10.49 per kWh. You’ll receive payments every quarter for 7 years, and they’ll be tax free. You can expect to earn between £902 and £1,061 per year from the RHI.

The amount you get paid per kWh is capped at 20,000kWh, however. As a rough guide, a 1-bedroom semi-detached house is likely to need around 8,000kWh of energy for heat per year, a 2-bedroom semi-detached house will need around 12,000kWh of energy, and a 3-bedroom detached house will need around 17,000kWh of energy – so most households shouldn’t reach the 20,000kWh payment cap.

You can receive RHI payments for more than one type of renewable technology: so, if you have an air source heat pump and solar thermal panels, you can receive payments for both.

How Do You Apply for the Renewable Heat Incentive?

Energy regulator Ofgem manages the RHI, so you’ll need to apply for the scheme through them. You can apply on the Ofgem website or by calling 0300 003 0744.

To apply, you’ll need:

  • your home’s Energy Performance Certificate (EPC), which must be no more than 2 years old
  • a certificate from your installer confirming that the installation is MCS approved
  • a document from your installer called the Installer Metering Questions.

Your air source heat pump must:

  • be Microgeneration Certification Scheme approved
  • appear on Ofgem’s product eligibility list
  • run on electricity
  • have a seasonal performance factor of at least 2.5
  • have a meter to monitor its performance.
Amy Catlow
Amy Catlow Publishing Director

As the self-proclaimed ‘Queen of Green’ Amy has been an environmental evangelist for as long as she can remember. Whether it’s crunching the data or helping visualise it, Amy has the nous to help you turn your home into an money saving eco-fortress.