The Pros and Cons of Using an Air Source Heat Pump

Air source heat pumps are very efficient at extracting the heat in the ambient air (even down to -15 o C) and delivering that heat to the internal space of a building. They can deliver heat to radiators, underfloor heating systems or warm air convectors, as well as provide hot water to the taps/ showers.

How does it work?

An air source heat pump works in the same way as a fridge extracts heat from the internal space, but in reverse. The system comprises of two coils (one inside and one outside), a compressor, refrigerant and an expansion device. The principle is that a lot of energy can be released when a gas is converted to a liquid. So, the external coil liquid absorbs heat and is converted to a gas which is then compressed. This high-pressure gas is then passed through the internal coil where it expands and turns back to a liquid, releasing energy in the process. The process is repeated many times to move the heat from outside to inside.

What are the benefits?

The system uses electricity to run the fans (that draw air over the coils) and compressors but this usage is far less than the amount of heat that can be moved by the system. In some cases, the heat energy transfer (measured in kW) is four times as great as the electrical power drawn by the fans and compressor, giving a Coefficient of Performance of 4:1. A typical gas boiler will have a Coefficient of Performance of less than 1:1 as more energy is put into the boiler than is useful in the heating system.

With a better Coefficient of Performance than other systems fuel bills will be lower and your carbon emissions will be reduced. In areas where there is no gas supply there are significant savings to be made i.e. no new pipework and no annual gas test inspections.

By having the internal coil placed within a water tank the system can heat the water ready for showers or taps, once at working temperature the system is very efficient at keeping the heat level required.

The Government are currently providing Renewable Heat Incentives (RHI) payments for new systems and these can reduce the running costs. Details of these change from time to time so do refer to the Government website for the latest incentives.

Most new Air source heat pumps come with a 2 or 3-year warranty but you should expect to get up to 20 years use out of them, if maintained properly. A yearly check of the system by an engineer is recommended but some manufacturers require on a 3 or 5 yearly check. Typical payback periods for a domestic property is around 4-5 years.

What are the negative points?

Air source heat pumps require some space, both internally and externally. Externally a space with good air circulation (no local foliage, etc.) is needed and inside space is needed for the water cylinder or cylinders, pumps, etc.

Planning permission may be required so it’s best to confirm with the local authority, who may ask for some technical details of the proposed system.

Air source heat pumps work best with underfloor heating systems (because of the lower water temperatures) however if radiators are specified they will need to be larger than normal. There will also be a need for electrical back up to act as a boost at peak load times.

There will be some external noise from the outside unit. This is normally kept down to a similar level as a typical air conditioning unit but this may seem loud if you’re in a quiet setting.

In areas where there is lots of flat exposed open space then a Ground source heat pump may be better suited. The benefits will vary with the type of ground and thermal properties and there will also be some digging involved but the energy savings could be even greater than an Air source heat pump.

Where gas is available at the building or site then generally, over the life-time of the equipment, a gas fired condensing boiler system has comparable efficiencies. If the building is poorly insulated then the savings will also be less.


Air source heat pumps are highly efficient systems and provide more heat to the building than the electrical power than they draw. They require only a small amount of maintenance and can operate for up to 20 years or more. They will lower your energy fuel bill and reduce your carbon footprint.

They do however need space for the equipment and have an external coil and fan that creates some noise. Over the life-time of the equipment gas fired condensing boilers can be as efficient so where gas is available this should be considered as an option.

Air source heat pumps are ideal in well insulated buildings, where there is no gas supply, and where underfloor heating can be utilised. They can be used with radiators and to heat up your hot water for taps and showers and come with saving through the Governments Renewable Heat Incentives.

If you need any advice about the best heating system to install in your property then please do get in touch by calling 0115 7788 227 or email

If you would like to find out more about how BEM Services can provide further advice about Air source heat pumps, then contact us by calling 0115 7788227 or email