Air source heat pumps under Part 14 Class G

Air source heat pump permitted development for a house comes from Class G of Part 14 of the General Permitted Development Order 2015. Provided the unit is within the volume limit, meets the noise standard, and the property is not listed or in one of the restricted categories, no planning application is needed. Amendments made in 2024 widened the right considerably in England, and a good deal of published guidance still describes the older, tighter rules.

The noise standard is the condition installers most often fail to evidence, and it is the one a council will ask about if a neighbour complains.

What Class G permits

Class G covers the installation, alteration or replacement of an air source heat pump on a dwellinghouse or a block of flats, or within the curtilage of either, including on a building standing in that curtilage.

The right is for a heat pump used for heating or cooling the building it serves. A unit installed to serve something else, a swimming pool building treated as a separate use, or a commercial operation run from the property, sits outside it.

Ground source and water source heat pumps sit in their own classes within Part 14 with different conditions, so do not read across from one to the other. And Part 14 applies to a dwellinghouse, which does not include a building containing one or more flats unless the class says so.

The volume limit and how the unit is measured

The limit is expressed as the volume of the outdoor compressor unit including its housing.

Measure the whole external enclosure, not the working parts inside it. An acoustic cover, a decorative surround or a purpose-built timber box added on site all count towards the volume, which catches installations where the box was added afterwards to reduce noise complaints.

Pipework, brackets and the condensate run are not part of the compressor unit. A buffer cylinder installed inside the house is irrelevant to Class G, because it is not outdoor equipment.

Where the calculated volume is close to the limit, get the manufacturer's dimensioned drawing rather than the marketing sheet, and keep it. The difference between a compliant and a non-compliant installation is often a few centimetres of casing.

What the 2024 amendments changed

Two changes made in England in 2024 matter to most householders.

The restriction preventing installation within one metre of the boundary of the curtilage was removed. That single change made many terraced and semi-detached properties workable, because on a narrow plot there was often nowhere more than a metre from a boundary.

The volume limit was increased from the previous figure to 1.5 cubic metres, which brings larger units and units with acoustic housings within the right.

Read the current consolidated text of Part 14 on legislation.gov.uk before relying on either point. Part 14 has been amended several times, guidance written before the change is still circulating, and the version in force is the one that decides whether your installation is lawful.

The conditions attached to Class G did not go away. The equipment must, so far as practicable, be sited to minimise its effect on the external appearance of the building and the amenity of the area, and it must be removed as soon as reasonably practicable when no longer needed.

The noise standard the installation must meet

Class G requires the installation to comply with the relevant microgeneration certification planning standards, or equivalent standards.

In practice that means the installer completes an assessment showing that the sound pressure level from the unit does not exceed 42 decibels at the assessment position, which is one metre from a habitable room window or door of a neighbouring property.

The calculation takes the manufacturer's sound power figure, the distance to the assessment position, and the effect of any barriers or reflecting surfaces. Placing a unit in a narrow passage between two houses can add several decibels through reflection, and an installation that would pass in an open garden fails in that position.

Three practical points.

The assessment position is at the neighbour's property, not at yours. A rear garden that feels remote from your own house may sit directly outside a neighbouring bedroom.

The standard is a condition of the permitted development right. Failing it does not attract a separate penalty. It means the installation was never permitted development at all, and the council can take enforcement action.

Ask the installer for the completed calculation sheet before the unit is ordered, and check that the assessment position they used matches the actual layout of the neighbouring property.

Where a unit cannot meet the standard in the only workable position, the route is a planning application supported by a Noise Impact Assessment that assesses the unit against the background sound level and proposes mitigation.

Conservation areas, listed buildings and article 2(3) land

Article 2(3) land, which covers conservation areas, National Parks, National Landscapes and World Heritage Sites, carries extra restrictions.

On that land, Class G does not permit installation on a wall or roof of the dwellinghouse which fronts a highway, and it does not permit installation nearer to a highway than any part of the dwellinghouse. A unit at the rear, out of sight, is normally still permitted.

Listed buildings are outside the right altogether in practical terms. Listed building consent is required for works affecting the special architectural or historic interest of the building, and that duty sits separately from the GPDO. Discuss the position with the conservation officer, and expect questions about pipe penetrations through historic fabric as much as about the unit itself.

An Article 4 direction can remove Class G in a defined area. Councils have made directions covering householder permitted development in conservation areas, and some are drawn widely enough to catch heat pumps. Check the council's register before you order equipment.

Flats, maisonettes and shared buildings

Class G extends to a block of flats, which was not always the case, but ownership usually decides the question first.

For a flat in a converted house or a purpose-built block, the external walls, the roof and often the garden are retained by the freeholder. Fixing equipment to them without consent is a breach of the lease whatever the planning position, and a landlord's consent process typically takes longer than a planning application.

Where several flats each want a unit, the amenity and noise picture changes. Cumulative sound from multiple compressors is assessed differently from a single installation, and a council faced with the fourth application on the same building will look at the total.

Communal or shared ground array systems avoid much of this, and they are a different consenting question again.

Keeping the evidence for a future sale

Permitted development produces no decision notice, so a purchaser's solicitor has nothing to inspect.

Keep four things: the manufacturer's dimensioned specification showing the unit volume, the completed noise assessment with the assessment position identified, the installation certificate, and dated photographs showing the position relative to boundaries and the highway.

Where the position is finely balanced, or where the property is in a conservation area, apply for a certificate of lawfulness for proposed development under section 192 of the Town and Country Planning Act 1990 before installation. It costs a modest fee, it takes eight weeks, and it converts a judgement into a document. A short Planning Statement setting the proposal against the Class G conditions is usually all the application needs.

A lawful development certificate is the only formal way to confirm that works are lawful, which is why it is worth the fee on any installation a future buyer might question.

You can browse all 66 PlanScope report types to see what a full application would need, or enter your postcode to check the designations affecting your property.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.