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Air source heat pumps explained

By Tom Morgan

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Air source heat pumps explained

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

Air source pumps serve as 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. 

There are other options available if you want to generate your own heat, however, such as wood burning stoves and solar panels. Heat pumps can save you more on your heating bills if you're replacing an electric, oil, LPG (liquefied petroleum gas) or coal system, rather than gas. But remember, a well-insulated home is essential – otherwise the heat the pump is generating escapes more easily.

Read on to find out more about the pros and cons of air source heat pumps, so you can decide whether getting one is the right decision for you.

Make sure you're not paying too much for gas and electricity. Our independent switching site, Which? Switch, will help you to find a cheap energy deal.

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How does an air source heat pump work? 

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.

Take a look at our graphic below for a visual representation of how an air source heat pump functions.

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 and air-to-heat.

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.

Air-to-water heat pumps

These 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.

They qualify for the Renewable Heat Incentive (RHI), too. Under the UK government's scheme, you could get money towards renewable heating costs in your home.

Air-to-water heat pumps may be best suited to new-build properties. It could cost less if the heat pump is included as part of the building specification, rather than having to retrofit underfloor heating later on.

Air-to-air heat pumps

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

What are the running costs? 

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. Read our guide on the Renewable Heat Incentive for more details.

Below, you'll see how much you could potentially save by replacing your existing system with an air source heat pump.

The EST also estimates annual RHI payments between £875 to £1,030 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 – £35 to £55 bill increase
  • Replacing a new (A-rated) oil boiler – £45 to £55 bill increase

Whether you decide to get an air source heat pump or not, make sure you are on the cheapest electricity tariff. Visit 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. 

They are also cheaper than ground source heat pumps. The Energy Saving Trust (EST) estimates that the cost of installing a typical ASHP system ranges between £6,000 and £8,000. 

In the summer, an air-to-air heat pump can operate in reverse. In other words, you can use it 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 and cons 

Air source heat pumps require little maintenance and can provide heating and hot water, but they aren't flawless systems. See the key advantages and disadvantages associated with using this heating system below:

Pros Cons
Energy efficient – air source heat pumps can generate less CO2 than conventional heating systems. Lots of space needed – you'll need enough space in your garden for the external condenser unit (comparable in size to an air-conditioning unit).
Easy to install – they are easier to install then ground source heat pumps, particularly for retrofit. Loud – condenser units can be noisy and also blow out colder air to the immediate environment.
RHI approved – they can qualify for the RHI, a financial incentive that pays you for generating your own heat through renewable technology. Electricity – 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.

Are air source heat pumps efficient? 

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, the figure 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.

Meanwhile, ground source heat pumps 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 

Regulation means that heat pumps have to have an energy label on them. 

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

Since 26 September 2015, all new heat pumps must be sold with an EU product label. The installer should also produce a package label that displays the efficiency based on 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.

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