Air Source Heat Pumps collects thermal energy from the outside air. The heat pump is located externally, either next to an outside wall, or connected to the property with pre-insulated pipes buried in a trench. The main internally located items are the hot water cylinder, a buffer tank and two expansion vessels.

As with all types of heat pumps, it is important to specify the right size (kW) heat pump. For this a room by room heat loss assessment of the property is required, along with individual Hot Water requirements for the property. A heat pump produces hot water and the lower temperature it can operate at, the more efficient the system is. Therefore, the overall efficiency of the heating system requires heating distribution (underfloor heating, radiators or fan coil units) which can deliver comfortable room temperatures at low operating temperatures.

FAQ's about Air Source Heat Pumps:

1. Where can the heat pump be located?

For a retrofit, the first location to consider would be outside a wall as close as possible to the current boiler location. For a new build, as close as possible to the plant room/installation cupboard. The heat pump needs to be located in a way which allows for a good flow of air through the unit. If placed parallel to a wall, the minimum distance to the wall is 200 mm. A minimum clear distance of 1-2 metres in front of the heat pump is required. If you consider sitting the heat pump close to an adjacent property, the noise impact has to be assessed. If no suitable location is found next to the property, it is possible to site the unit at a distance from the outside wall. This will require the heat pump to be connected to the property with a high spec pre-insulated pipe buried in a trench.

2. Are they noisy?

All air source heat pumps emit a noise. We use heat pump from the manufacturers Nibe, & Stiebel Eltron for almost all our installations. One of the reasons we like to use Nibe, & Stiebel Eltron is that the noise level is very very low. However, sensitivity to noise is very individual. If you are concerned about the noise, we are happy to take you to an installation and listen to the unit.

3. What equipment is required inside the house?

You will need a hot water cylinder, a buffer tank (40 or 100 litre depending on the size of heat pump) and an expansion vessel. This can all come encased in an internal unit directly from the manufacturers which looks nice and tidy in any plant room.

4. What are the planning requirements?

The installation of an air source heat pump on domestic premises is considered to be permitted development, not needing an application for planning permission, provided ALL the limits and conditions listed below are met. These permitted development rights apply to the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage (garden or grounds) of a house or block of flats, including on a building within that curtilage. A block of flats must consist wholly of flats (e.g. should not also contain commercial premises).

Limits to be met:

  • Development is permitted only if the air source heat pump installation complies with the Microgeneration Certification Scheme Planning Standards (MCS 020) or equivalent standards.
  • The volume of the air source heat pump’s outdoor compressor unit (including housing) must not exceed 0.6 cubic metres
  • Only the first installation of an air source heat pump would be permitted development, and only if there is no existing wind turbine on a building or within the curtilage of that property. Additional wind turbines or air source heat pumps at the same property requires an application for planning permission
  • All parts of the air source heat pump must be at least one metre from the property boundary Installations on pitched roofs are not permitted development.
  • If installed on a flat roof all parts of the air source heat pump must be at least one metre from the external edge of that roof
  • Permitted development rights do not apply for installations within the curtilage of a Listed Building or within a site designated as a Scheduled Monument On land within a Conservation Area or World Heritage Site the air source heat pump must not be installed on a wall or roof which fronts a highway or be nearer to any highway which bounds the property than any part of the building
  • On land that is not within a Conservation Area or World Heritage Site, the air source heat pump must not be installed on a wall if that wall fronts a highway, and any part of that wall is above the level of the ground storey.

The air source heat pump must be:

  • Used solely for heating purposes
  • Removed as soon as reasonably practicable when it is no longer needed for microgeneration
  • Sited, so far as is practicable, to minimise its effect on the external appearance of the building and its effect on the amenity of the area.
  • You may wish to discuss with the Local Planning Authority for your area whether all of these limits and conditions will be met.


For further details of our heat pump installation services.