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Air Source Heat Pumps: What to Consider

This article explains why opting for an air source heat pump as a home heating method is becoming increasingly popular. It summarises the way that they work before considering the pros and cons.

If the right design is installed, an air source heat pump can provide all hot water and heating requirements. They are a low carbon way to heat a home, absorbing heat from a cooler place and using it to increase the heat inside a house.

The technology enables the generation of renewable heat and offers potential savings on energy bills. To maximise efficiency, a home must be well insulated, otherwise the heat escapes. The pumps are similar in appearance to an air conditioning unit and are usually sited on the outside of a house.

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 to increase its temperature before then condensing it back into a liquid and releasing stored heat to radiators or underfloor heating.

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

Pumps 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, as the temperature falls, they will use more electricity, making it important to select a pump that will perform as required in winter.

Air source heat pumps can cost around 10% less to run annually than a gas system and offer savings on heating bills if they replace systems such as electric storage heaters, oil, LPG liquified petroleum gas, or coal. However, they deliver heat at lower temperature than gas and oil boilers, so the pump needs to run for longer to deliver the required heat.

The property industry is preparing for widespread take-up of the technology. 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 PV 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 two main types of air source heat pump:

Air-to-water and air-to-air pumps are both highly efficient and can reduce energy bills.

Air-to-water heat pumps:

Heat is taken from the outside air and fed to a wet central heating system to heat radiators, underfloor heating and generate 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. It is easier to incorporate large radiators or underfloor heating when extending a home or in a new-build and can cost less than retrofitting underfloor heating later. Such systems cost between £8,000-£18,000; installation is complex and may involve redesigning an existing system.

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. Payments are made over seven years and the scheme closes to new applicants at the end of March 2022.

Air-to-water heat pumps may reduce a carbon footprint by 50% (Greenmatch.co.uk) and a 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 efficiency of the system, the type of heating 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 (Greenmatch.co.uk). Air-to-air heat pumps take heat from the outside air and feed it into the home through fans which produce moderate noise levels.

They operate most effectively where there is a flow of internal air such as an open plan design which helps move the heat around. They cannot produce hot water and are not eligible for RHI payments. In summer an air-to-air pump can operate in reverse and be used 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 finished in a day. They are low maintenance, requiring an annual check and do not produce carbon. Air-to-air pumps operate according to the outside air temperature, working most efficiently when this is between 0°-10°C; in colder temperatures, the pump will use more electricity.

Advantages of air source heat pumps:

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

Disadvantages of air source heat pumps:

  • 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 pump, they are not zero-carbon (unless electricity comes from a solar panel or other 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:

Pumps are usually sited externally as the air needs space to circulate. Listed buildings or conservation areas may require planning consent for installation, and it is advisable to ensure that the work will meet Building Regulations. An accredited installer must be used to ensure qualification for RHI payments. Once installed, a Commissioning Certificate should be obtained from the installer and a Microgeneration Certification Scheme (MCS) installation certificate once it is registered, which is required to qualify for funding schemes. All pumps certified by the MCS must also bear a product label to be eligible for RHI.

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

As part of its Heat and Buildings Strategy, the government has established a £450 million, three-year Boiler Upgrade Scheme; from April 2022, homeowners can obtain grants of £5,000 to install more efficient, low carbon heating systems. The government is also investigating the potential role for hydrogen in heating houses; it is monitoring trials and is expected to make a decision on this 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 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 industries 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.”

Do you have an air source heat pump?

If you have a positive or negative experience of an air source heat pump, we would love to hear about it to share with our readers – do get in touch!

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