The Ultimate Guide To Air Source Heat Pumps

As energy costs continue to rise and the emphasis on working towards creating a greener, more carbon neutral way of life increases you’ll no doubt have heard a wide array of terms relating to renewability, sustainability and energy efficiency. When it comes to the way in which we heat, or potentially cool, our houses, those terms will likely have included things such as ‘biomass boilers’, ‘heat pumps’ and ‘solar water heating systems’.

In this post we’ll be focusing on ‘heat pumps’, or more specifically ‘air source heat pumps’ (ASHP’s), identifying exactly what they are, the varying types including how they work as well as the potential advantages and disadvantages of choosing to install them at your home, business or development.

Choosing the right air source heating system for your commercial or domestic requirements can be a daunting prospect. With more than 15 years providing energy conservation consultancy services Falcon Energy is perfectly placed to help you do just that, and in addition to performance estimation, cost analysis and bespoke system design we also offer complete MCS (Microgeneration Certification Scheme) certified installation packages.

Call us today on 01403 253439, or complete our online contact form to see how you could benefit from our MCS air source heat pump installation package.

What is an air source heat pump?

An air source heat pump system is a reversible heat pump which facilitates the heating, or cooling, of a room or building.

Unlike many conventional heating systems which burn fossil fuels (think the traditional gas boiler, oil boiler etc) to generate heat for your central heating system, non-traditional heating systems like air source heat pumps require only the heat from the outside air (and, depending on a number of factors, electricity) to operate.

How do air source heat pumps work?

Air source heat pumps are mechanical systems which allow the transfer of thermal energy from one location at a cooler temperature (the source) to an alternate location at a higher temperature (the sink, or heat sink).

This process in which heat is transferred in the opposite direction, as would be normal for heat transfer without an additional external power source, is known as the refrigeration cycle, or thermodynamic heat pump cycle.

How an air source heat pump works:

  1. When used as ‘heaters’ air source heat pumps absorb thermal energy from an external source via a collector system, through which a refrigerant is passed (typically a gas such as R407C, R32, R410a and R417a) essentially ‘collecting the heat’.
  2. Upon absorbing the heat the refrigerant within the cycle boils and vaporises, creating steam which is compressed to further raise the temperature within the cycle.
  3. The resulting heat is then passed through the system to the heating circuit, whereby it can be used to heat the room or building.


There are two types of air source heat pump: air-to-water pumps and air-to-air pumps. When used as an air conditioner, or ‘cooler’ the air-to-air system works in reverse to transfer heat from inside the building to the outside. This cannot be replicated by air-to-water heat pumps.*

Air source heat pumps are examples of HVAC (Heating, Ventilation and Air-Conditioning) systems.

What types of air source heat pump are there?

‘Air-to-water’ heat pumps

The most commonly installed air source heat pumps are the ‘air-to-water’ variant. As the name would suggest they transfer thermal energy from the exterior of a building to heat water, which is then used to heat a building via the central heating system.

Because air source heat pumps typically generate less heat than a conventional boiler they are often best used alongside heating circuits with large surface areas, for instance an underfloor heating system. In some instances existing radiators are too small to effectively transfer the heat generated by the pump.

These systems qualify for the UK Governments RHI (Domestic / Non-domestic Renewable Heat Incentive).

‘Air-to-air’ heat pumps

‘Air-to-air’ heat pumps, as you’ve no doubt concluded, work in exactly the same way but require a warm air circulation system to operate. As the air is heated directly the ‘warm up’ time is relatively short.

These systems do not qualify for the UK Governments RHI (Domestic Renewable Heat Incentive).

What are the advantages and disadvantages of air source heat pumps?

Advantages of air source heat pumps

Reduced carbon footprint

Air source heat pumps are a low carbon alternative to gas, LPG and other electrical heating systems. As we collectively aim towards ‘Net Zero’ there are calls from The International Energy Agency to stop the sale of new gas boilers by 2025.

High Seasonal Coefficient of Performance (SCOP)

The coefficient of performance (COP) of air source heat pumps when the external temperature is 7°C and above is calculated at 3.2. Effectively this means that the system is running at 320% efficiency; for every 1kWh of electricity required to operate the system it produces 3.2kWh heat.

The seasonal coefficient of performance (SCOP) takes into account fluctuations of the external temperature, and thus is dependent on the location and climate of the heat pump. Air source heat pumps can operate in temperatures as low as -20°C, however they begin to lose efficiency progressively as the temperature decreases.

Eligible for RHI*

Air-to-water heat pumps are eligible for the Government’s RHI scheme (Domestic / Non-domestic Renewable Heat Incentive). Air source heat pumps currently qualify at a rate of 10.85pence per kW for the first 7 years after installation. The RHI is set to end in March 2022, but is expected to be replaced by an alternate scheme.

Long lifespan

Depending on maintenance, location and climate, the life expectancy of air source heat pumps can often exceed 20 years, a relatively long period when compared to the 10-15 year life expectancy of a traditional gas or oil fired boiler.

Low maintenance

Air source heat pumps typically require less maintenance, and less frequent replacement of costly parts than traditional boilers and other renewable energy sources such as wind turbines and solar PV. However, as with all heating systems we advise referring to the manufacturers recommendations regarding safety and servicing requirements.

Can be used for both heating and cooling*

Air-to-air heat pumps have the unique capacity to provide both heating and cooling, mitigating the requirement for two separate systems. Some air source heat pumps are also able to provide both space heating and hot water. These systems will need to run with higher flow temperatures than those that provide space heating only.

Disadvantages of air source heat pumps

Less heat output than traditional boiler systems

When compared with conventional boiler systems air source heat pumps produce a lower heat supply. Gas boilers for instance may run with a flow temperature of 70°C, with water entering the heating circuit at 70°C and exiting at 60°C. An air source heat pump may run with a flow temperature of only 35-45°C, and whilst they typically only lose around 5°C throughout the circuit they are unable to produce the same heat output as the gas boiler.

Possible costs incurred for installing underfloor heating / larger radiators

Because of the decreased heat output existing radiators need to be replaced with larger models to increase the heated surface area, and many choose to combine the air source heat pump with underfloor heating systems. These costs can be considerable, particularly if underfloor heating is applied retrospectively.

Building must be well insulated

In some circumstances air source heat pumps are unable to provide the level of heat required to warm a poorly insulated building. Although this is no different to most heating systems it is worth noting, and particularly relevant to older properties.

Potential for reduced efficiency dependent on external temperature

Air source heat pumps work most efficiently when there is minimal difference between internal and external temperatures. As the difference between these temperatures increases they become less efficient and require more electrical energy in order to operate.

How much do air source heat pumps cost?

Purchase and installation costs vary considerably, and will be reflective of the size of pump required as well as other factors, but you can expect to pay somewhere in the region of £5000-£20,000. Speak to one of our energy consultancy experts today for a free, no obligation estimate for your commercial / non commercial premises.

Things to consider before installing an air source heat pump

Find a reputable installer

As previously mentioned, installing an air source heat pump at your property can range in costs. Ensuring you have a reputable installer will give you peace of mind that you’re getting the very best service and an efficient heating system that is compliant with all regulations.

At Falcon Energy, we’re an MCS certified installer, hold all the relevant qualifications for heat pump installation and are approved installers of Mitsubishi air source heat pumps. You can rely on our team of professionals to offer a compliant and trustworthy service.

Seasonal temperature fluctuations

For an air source heat pump to work with maximum efficiency the fluctuations in external temperature should ideally be minimal. If your proposed installation site experiences large seasonal changes in temperature it may be worth considering an alternate heating system, for example a ground source heat pump.

Level of insulation

For similar reasons, buildings (typically older) with poor levels of insulation are often not best suited to air source heat pump systems. The potential reductions if carbon emissions and financial savings on energy bills are minimal in these circumstances.

Improving the insulation and efficiency of the property will ensure air source heat pumps work optimally, but this will mean you incur an extra cost before installation. However, this will be of benefit in the long run, as you’ll reduce energy loss from your property and enjoy lower energy bills.

Space required

The average gas boiler may measure approximately 750mm x 450mm x 300mm. MORE INFORMATION NEEDED

Suitable heating circuit

Air source heat pumps are perfectly suited to properties with existing underfloor heating or larger radiator systems. Otherwise you’ll incur extra costs of adapting systems to work efficiently with the air source heat pump.


How noisy are air source heat pumps?

Air source heat pumps will typically generate more noise than ground source heat pumps. However, with the average noise levels within 1 metre of the unit ranging from between 40-60 decibels this is still far from a problematic level of noise.

Air source heat pump installations are subject to the following building regulations requirements: “The distance at which the noise level from each of the measured ASHPs is reduced to below the façade level of LAeq 45 dB” [Source]

To put this in perspective 45db is thought to be equivalent to the hum generated by a refrigerator.

How efficient are air source heat pumps?

Air source heat pumps operate with a coefficient performance rating of 3.2 when the external temperature is 7°C and above. This means that the system is running at 320% efficiency; for every 1kWh of electricity required to operate the system it produces 3.2kWh heat.

What grants are available for air source heat pumps?

Renewable Heat Incentive (RHI)

Air source heat pumps installed before March 2022 (subject to certain requirements) are eligible for the Government’s Renewable Heat Incentive scheme. Payments are made quarterly for 7 years from installation based upon the amount of renewable energy produced by your heat pump. Find out more here.

Boiler Upgrade Scheme

From March 2022 the RHI scheme is to be replaced by the Boiler Upgrade Scheme. This scheme will provide capital grants for the installation of heat pumps, “…and in some circumstances biomass boilers, in homes and some non-domestic buildings”. Find out more here.

What’s the difference between air source heat pumps and ground source heat pumps?

Although an air source heat pump (ASHP’s) and a ground source heat pump (GSHP’s) utilise the same technology, the source from which they draw heat differs. ASHP’s draw heat from the outside air whilst GSHP’s draw heat from the ground.

Do air source heat pumps work with solar panels?

Absolutely. Whilst air source heat pumps are low carbon heating alternatives, they still require some amount of electricity in order to operate. Generating that electricity through a renewable energy source further reduces the carbon emissions created.

Book a free air source heat pump consultation

If you’d like to find out more about how you could reduce your carbon footprint whilst creating financial savings, give our team a call on 01403 253439. Our air source heat pump installation packages include:

  • Full site survey and bespoke design of the system
  • Supply of the air source heat pump, accessories, DHW cylinder & buffer tank (if required)
  • Heat loss calculations
  • Performance estimate and cost analysis
  • Commissioning of all equipment
  • Certification for the domestic Renewable Heat Incentive/Government Grant
  • MCS compliance certificate
  • Heat pump installations, if required
Posted in Sustainability.