A guide to air source heat pumps

This article explains why opting for an air source heat pump as an efficient alternative home heating system is becoming increasingly popular. It summarises:

  • how heat pumps work and how they can heat your home
  • running costs and how they can significantly reduce heating bills
  • the future take-up of air source heat pump technology
  • the two main types of air source heat pump
  • the typical cost of installing heat pumps
  • air source heat pumps’ disadvantages and advantages

So, if you are thinking about how to make your house more energy efficient and are considering an air source heat pump, dive in!

What can an air source heat pump do?

If the right design is installed, an air source heat pump can provide hot water and heating requirements in most homes. They are an energy efficient, low carbon way to heat a home and can save money on an annual fuel bill. Heat pumps work by absorbing heat from a cooler place and using it to increase the heat inside a house to create ambient warmth.

Installing an air source heat pump enables the generation of renewable heat and the potential to save on electricity bills in a property suitable. To maximise efficiency, it is important to have a well-insulated house, otherwise the heat escapes: good loft insulation is vital and measures such as wall insulation and triple glazing may be worth considering. Air source heat pumps are similar in appearance to an air conditioning unit and are usually sited on the outside of a house where there is enough space to allow cool air to circulate.

How does an air source heat pump work?

Air source heat pumps work like a refrigerator in reverse; they absorb heat from the outside air and using electricity, the pump compresses the liquid refrigerant to increase its temperature before condensing it back into a liquid. Stored heat energy is then released to radiators or an underfloor heating system.

The remaining heat generated can be stored in a domestic hot water cylinder and used for showers, baths and taps. Air source heat pumps are designed for small to medium sized homes so single phase or 3-phase electricity is suitable, however, the addition of a heat pump system will increase electricity usage which might be relevant if a house uses numerous electrical items.

Heat pump systems should use less electrical energy than the heat they produce, making them energy efficient. They work even if the outside temperature is below zero, however, when the temperature drops, they will use more electricity, so it’s important to select a heat pump system that will work efficiently in cold climates.

Air source heat pump running costs

Heat pumps costs around 10% less to run annually than a gas system and could save on household energy bills if you are replacing a fossil fuel system. While heat pumps can be attractive as they could save on energy prices, they deliver heat at lower temperatures than a modern natural gas boiler, so must run for longer to deliver the required heat output.

Heat pump systems to be the `new norm’

The property industry is preparing for widespread take-up of this renewable energy source. Tim Kampel, director of property service provider Box Property Solutions commented:

“Air source heat pumps will be the new norm. As we switch away from gas, air source heat pumps are currently the best choice and ideal for off-grid solutions. We would recommend also installing solar panels to offset the carbon created by the power demand of the air source heat pump for a much better, green solution throughout.”

“However, there are two things to consider if switching; firstly, the location of the unit as they can be quite big and unsightly and secondly, radiator resizing or switching to underfloor heating as the water is heated to a much lower temperature with a heat pump and this can incur substantial electricity costs.”

The government is consulting on ending the installation of new fossil fuel systems in England from 2026 for all properties without mains gas. This could mean that those living in rural areas would have to replace an oil boiler, lpg boiler or electric storage heaters with a heat pump – the preferred choice – possibly a decade earlier than those without a gas connection.

Currently, 1.1 million homes in England don’t have access to mains gas and use fossil fuels for heating. A consultation proposal is that if a householder without a gas connection has a boiler break down after 2026, they must install a new non-fossil fuel system, but householders on the gas grid can replace boilers with a like-for-like system until 2035.

Air source heat pumps positioned on an exterior wall to absorb heat from the air.

The two main types of air source heat:

Both air-to-water and air-to-air pumps are highly efficient domestic heat pump systems and can reduce carbon emissions and reduce energy bills in a well-insulated home. They are typically used in passivhaus designs which optimise a house’s energy efficiency to provide an ambient temperature, heating and hot water.

Air-to-water heat pumps:

Heat pumps extract heat from the air outside and feed it into a wet central heating system to heat existing radiators, underfloor heating systems and provide hot water. Air-to-water heat pumps are more efficient at lower temperatures than a standard boiler system. They are most suited to large radiators or water underfloor heating, as the heat they produce is cooler than that from a conventional gas or oil boiler and a large surface area is needed to release the heat output.

It’s easier to incorporate larger radiators or underfloor heating when extending a home, or in new-builds and can cost less than retrofitting underfloor heating later. The typical cost is between £8,000-£18,000; installation is complex and may involve redesigning an existing conventional heating system.

While air-to-water heat pumps qualify for the government’s Renewable Heat Incentive (RHI), which makes payments for the installation of certain types of renewable heating to help offset the costs, the scheme closed to new applicants in March 2022. RHI payments are made over seven years.

Air-to-water heat pumps may reduce a carbon footprint by 50% ( and a heat pump can last for 13-20 years. A small amount of electricity will be used but running costs are minimal; the payback time depends on the pump’s efficiency, the type of system being replaced and the price paid for electricity.

Air-to-air heat pumps:

These can provide both heating and cooling and can enable up to three times higher heating efficiency ( Air-to-air heat pumps take heat from the outside air and feed it into the home through fans which produce moderate noise levels.

Air-to-air heat pumps operate most effectively where there is a good flow of internal air such as an open plan design which helps move the warm air around. They can’t produce domestic hot water and are not eligible for RHI payments. In summer, an air-to-air heat pump can operate in reverse and be used to as an air conditioning unit.

This system can be used to boost a conventional heating system. An air-to-air system costs between £1,600 and £3,100; installation is simple and often can be completed in a day and they have lower running costs. An annual check is required. Air-to-air pumps operate according to the outside air temperature, working most efficiently when this is between 0°-10°C; in low temperatures, the pump will use more electricity.

How much does an air source heat pump cost?

Most heat pumps for a detached house cost between £8,000-£16, 000, and for a semi-detached property, from £7,000-£10,000. While the upfront cost is more than for anew gas or oil-fired central heating system, air source heating technology has a longer lifespan. The cost of installing an air source heat pump needs to be added and will depend on the size of the house and type of pump. They are less expensive to install in a new build house and can be costly as part of a retrofitting scheme in an existing house. Using a professional heat pump installer is advised.

Key advantages of air source heat pumps:

  • Little maintenance and they can provide heating and hot water in most houses
  • Heat pumps are a low carbon heating source
  • Energy efficient – heat pump systems generate less Co2 than many conventional heating systems
  • Savings on annual energy bills compared to some older fossil fuel burning systems
  • The design can work with any building construction
  • Help lower carbon footprint as a renewable heat source is used– i.e., air
  • No fuel deliveries are needed

Air source heat pumps disadvantages:

  • Sufficient space is required for the external condenser unit
  • Condenser units can be noisy and blow cold air into area immediately around them
  • As electricity is needed to drive the heat pump, they are not zero-carbon (unless electricity comes from solar or another energy source)
  • Servicing is required every 2-3 years
  • Heat pumps must have an energy label on them stating how energy efficient the pump is on a scale from dark green (most efficient), to red (least efficient)

Air source heat pump installation:

There are different types of pump and the system design chosen must be able to cater for the property size. Accurate measurements of the space inside must be taken. A professional heat pump installer should be used to ensure the pump is installed correctly.

Heat pumps are usually sited externally as the air needs space to circulate around them. Listed buildings or conservation areas may require planning permission for installation, depending on the local authority. It’s advisable to ensure that the work will meet Building Regulations requirements.

Once installed, a Commissioning Certificate should be obtained from the installer and a Microgeneration Certification Scheme (MCS) installation certificate once the heat pump is registered, which is required to qualify for funding schemes. All heat pumps certified by the MCS must also bear a product label to be eligible for the Renewable Heat Incentive.

The cost of installing a heat pump will reduce

Richard Beresford, chief executive of the National Federation of Builders, said that with demand for air source heat pumps set to escalate, when the supply and fitting chain is fully in place, installation costs will come down.

The Government’s Boiler Upgrade Scheme – a £450 million, three-year branch of its Heat and Buildings Strategy – means that from April 2022, homeowners could obtain grants of £5,000 to install more efficient, low carbon systems. The government is also investigating the potential role of hydrogen in heating houses; trials are ongoing and a decision on this is expected by 2026. Mr Beresford concluded:

“The Government is correct to kickstart the heat pump industry, but it needs to consider how other solutions such as ground source, solar panels and wind need to be part of the mix. This will be key in generating the electricity needed for decarbonisation and means they must immediately reassess their onshore renewable approach.

“However, the most important challenge is the need to retrofit English and Welsh homes so that heat pumps use less energy and homes are healthier and warmer. The Government needs to engage with the industry’s National Retrofitting Strategy and recognise, that at no cost to the taxpayer, the planning and policy elements of it will kickstart our essential retrofitting sector.

Have you invested in an air source heat pump?

Has installing a heat pump system reduced your annual energy bills?

Does it provide enough heating and hot water?

If you would like to comment on air source heat pumps’ disadvantages or advantages, we would love to hear about it to share with our readers – please leave a comment on our contact page.

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