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Air source heat pumps explained

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Air source heat pumps explained

Find out how air source heat pumps work, how much air source heat pumps cost, and how much they could save you on your energy bills.

Air source pumps are an alternative way to heat your home, and could be the ideal solution if you want to generate your own heat and potentially save money on your energy bills. 

Aside from air source heat pumps, there are other options available if you want to generate your own heat - such as wood burning stoves and solar panels. Read on to find out more about air source heat pumps, including their pros and cons, so you can decide whether getting one is right for you.

Make sure you're not paying too much for energy. Use our independent switching site, Which? Switch, to find a cheap energy deal.

How an air source heat pump works

An air source heat pump is usually placed outdoors at the side or back of a property. It takes heat from the air and boosts it to a higher temperature using a heat pump. The pump needs electricity to run, but it should use less electrical energy than the heat it produces. 

Many air source heat pumps are eligible for payment through the Renewable Heat Incentive, a government scheme that provides payments to homeowners who generate their own heat. 

Types of air source heat pumps

There are two main types of air source heat pumps (ASHPs):

Air-to-water heat pumps

Air-to-water heat pumps take heat from the outside air and feed it into your wet central heating system. As the heat produced is cooler than that from a conventional boiler, you may need to install larger radiators or underfloor heating in your home to make the most of it.

Air-to-air heat pumps

Air-to-air heat pumps take heat from the outside air and feed it into your home through fans. This type of system cannot produce hot water.

Air source heat pump hints and tips

  • Air-to-water ASHPs work better with underfloor heating systems. If underfloor heating is not possible, large radiators should be used. This is because the heat generated by the heat pump is not as high as that produced by a conventional boiler, so a larger surface area is needed to achieve similar temperatures in your home.
  • Air-to-water heat pumps could be better suited to new-build properties than retrofit. This is because costs could be reduced if the heat pump is included as part of the building specification, rather than having to retrofit underfloor heating later on.
  • Heat pumps can save you more on your heating bills if you're replacing an electric, oil, LPG or coal system, rather than gas.
  • A well-insulated home is essential - otherwise the heat the pump is generating escapes more easily.
  • Once in place, the heat pump should require little maintenance.
  • Air-to-water heat pumps qualify for the Renewable Heat Incentive.

Air source heat pump costs and savings

ASHPs are cheaper than ground source heat pumps. The Energy Saving Trust (EST) estimates that the cost of installing a typical ASHP system ranges between £7,000 and £11,000. 

The payback period (the time taken to recoup the cost of the system in energy savings) depends on how efficiently your system works, the type of heating system you're replacing, whether you can get money with the RHI and how you'll be using the heat generated by the pump. 

If replacing an old heating system, the EST says that an average performing air source heat pump in a four-bedroom detached home could save:

  • Replacing oil (non-condensing) - between £290 to £315
  • Replacing gas (non-condensing) - between £455 to £485
  • Replacing LPG (non-condensing) - between £1,000 to £1,090
  • Replacing electric (old storage heaters) - between £735 to £820

The EST also estimated the RHI would pay an extra £1,140 to £1,235 a year.

But if you’re replacing a new heating system, an air source heat pump could actually work out more expensive:

  • Replacing a new (A-rated) gas boiler - £10 to £15 bill increase
  • Replacing a new (A-rated) oil boiler - £155 to £165 bill increase

Whether you decide to get an air source heat pump or not, make sure you are on the cheapest electricity tariff for your home. Use an independent switching site, like our own Which? Switch, to compare electricity deals.

Installing an air source heat pump

ASHPs look similar to air-conditioning units. They are less disruptive to install than ground source heat pumps, as they do not require any digging in your garden. 

An ASHP works a bit like a refrigerator in reverse. The process consists of an evaporator, a compressor and a condenser. The ASHP absorbs heat from the outside air into a liquid at a low temperature, then the heat pump compressor increases the temperature of that heat. In the condenser, the hot liquid's heat is transferred to your heating and hot water circuits. So you can use it to warm up your home.

In the summer, an air-to-air heat pump can be operated in reverse. So it can be used like an air-conditioning unit to provide cool air for your home.

If you're considering installing an air source heat pump, you can find a local, trustworthy installer through Which? Trusted Traders.

Pros of air source heat pumps

  • Air source heat pumps can generate less CO2 than conventional heating systems.
  • They are cheaper than ground source heat pumps, although their efficiency can be lower. 
  • Air source heat pumps are also easier to install then ground source heat pumps, particularly for retrofit.
  • ASHPs can provide heating and hot water.
  • They require very little maintenance.
  • Some can be used for air conditioning in the summer.
  • ASHPs can qualify for the RHI, a financial incentive that pays you for generating your own heat through renewable technology.
  • You need to use electricity to power the pump which circulates the liquid in the outside loop. But for every unit of electricity used by the pump, you get between two and three units of heat – making this an efficient way to heat a building.
  • Cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump.

Cons of air source heat pumps

  • You'll need enough space in your garden for the external condenser unit (comparable in size to an air-conditioning unit). 
  • Condenser units can be noisy and also blow out colder air to the immediate environment.
  • You still need to use electricity to drive the pump, so an air source heat pump can't be considered completely zero-carbon unless this is provided by a renewable source, such as solar power or a wind turbine.

 Alternatively, consider solar photovoltaic panels or a wind turbine (if you are in a suitable area) for a greener source of electricity

How green are air source heat pumps?

An air source heat pump system can help to lower your carbon footprint as it uses a renewable, natural source of heat – air. The amount of CO2 you'll save depends on the fuel you are replacing. For example, it will be higher if you are replacing electric heating rather than natural gas.

A heat pump also requires a supplementary source of power, usually electricity, to power the heat pump, so there will still be some resulting CO2 emissions.

Ground source heat pumps are also available. They draw heat from the ground via a network of water pipes buried underground, usually in your garden. For more details, see our separate guide to ground source heat pumps.

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Heat pump energy labels

New regulation means that heat pumps will now have to have an energy label on them. 

The label gives information about the energy efficiency of the heat pump and rates products from dark green (most efficient) to red (least efficient).

All new heat pumps must be sold with an EU product label, since 26 September 2015. The installer should also produce a package label that displays the efficiency based upon several different components in the heating system.

After 25 March 2016, all heat pumps certified by the Microgeneration Certification Scheme must be sold with a product label, and the installer must produce a package label. If your heat pump is not sold with a product label it may not be eligible for the RHI.