Heat pump siting limits under Part 14 Class G

Most air source heat pump installations on a house in England are permitted development, which means no planning application. The right is Class G of Part 14 of Schedule 2 to the General Permitted Development Order 2015, and it comes with conditions rather than a free pass. The two that catch people out are the noise requirement, which is assessed at your neighbour's window rather than at your own, and the restrictions that apply in a conservation area or to a listed building.

Class G has been amended more than once, most recently to relax the distance from the boundary and to increase the permitted size of the outdoor unit. So check the current text of Part 14 before you fix a position, and be careful with installer guidance or an article written against an older version of the Order.

What Class G permits

The right covers the installation, alteration or replacement of an air source heat pump on a dwellinghouse or block of flats, or within its curtilage, subject to conditions. Two run through everything else.

The installation has to comply with the microgeneration certification scheme planning standards for air source heat pumps, or an equivalent standard. That document is where the noise requirement lives.

The heat pump has to be used solely for heating purposes. A unit providing cooling as well as heating falls outside the right, which matters with some air-to-air systems.

There is also a tidying-up condition: the equipment has to be removed as soon as reasonably practicable when it is no longer needed for microgeneration.

The limits on size and position

The limits are about volume and where the unit sits.

Volume means the volume of the outdoor unit including its housing, not the footprint. Manufacturers publish dimensions, so the check is arithmetic, and a monobloc unit on a low plinth with an acoustic enclosure can be larger than the bare unit suggests.

Position deserves more thought than it usually gets. Airflow needs clear space in front of the fan, defrost water needs somewhere to drain in winter, and a unit tucked into a narrow side passage between two houses can both perform badly and concentrate noise against the neighbouring wall.

The noise condition and how it is checked

This is the condition that decides whether an installation is lawful, and installers sometimes treat it as a formality.

The planning standards set a sound level limit assessed at a position outside the nearest habitable room of a neighbouring property, commonly expressed as 42 decibels. The calculation combines the manufacturer's declared sound power level with the distance to the assessment position and corrections for the surrounding surfaces, such as a wall behind the unit or a corner that reflects sound in two directions. The version of the standard matters, so use the current one.

What that means in practice:

• A terraced or semi-detached house with a narrow side passage is the hardest case, because the assessment position can be a few metres away with two reflecting surfaces.
• Moving the unit a couple of metres, or turning it, often changes the result more than buying a quieter model.
• An acoustic enclosure or barrier can bring a marginal case inside the limit, provided it does not restrict airflow.
• Where the calculation does not pass, the installation is not permitted development, and the route is a planning application.

Ask the installer for the completed calculation sheet, not a statement that the unit complies. It is a short document and it is the evidence you will want if a neighbour complains.

Conservation areas, listed buildings and Article 4

Three separate restrictions, and they overlap.

In a conservation area or a World Heritage Site, the right does not extend to a unit on a wall or roof forming the principal elevation or a side elevation fronting a highway, and it does not extend to an outbuilding within the curtilage. A rear garden position is usually the workable answer.

Within the curtilage of a listed building, Class G does not apply at all, so planning permission is needed. Listed building consent is a separate consent again, required for works affecting the building's special interest, and it can be needed even where the unit is free-standing if pipework passes through historic fabric. The balance an officer weighs in those cases is set out in our note on listed building energy efficiency and the planning balance, and a Heritage Statement is the document that carries the argument.

An Article 4 direction can remove the Class G right for a defined area. Directions are recorded by the council and shown on the local plan's constraints mapping, so check before ordering equipment.

Where a full application becomes necessary

Five situations, in rough order of how often they arise.

1. The noise calculation does not meet the standard at the neighbouring assessment position.
2. The unit would go on a front or highway-facing elevation in a conservation area.
3. The property is a listed building or within its curtilage.
4. An Article 4 direction removes the right.
5. The unit provides cooling as well as heating, or serves something other than a dwelling.

A householder application is the usual route, and the fee is modest compared with the installation. The case is straightforward: a plan showing the position and the distance to neighbouring windows, an elevation, the manufacturer's data, an acoustic assessment, and a short statement on the visual effect and the carbon benefit.

Evidence for a noise sensitive position

Where the assessment is marginal, or where a neighbour has already objected, put proper evidence in.

A Noise Impact Assessment for a domestic heat pump is a short piece of work: the declared sound power level, the propagation calculation to each nearby habitable room window, the reflection corrections, the background sound level in the garden at night if it has been measured, and the effect of any proposed enclosure. Where the plant runs harder in cold weather, say what the level is under that condition rather than at a mild-weather rating.

Two practical measures worth proposing in the application. An anti-vibration mounting detail, because structure-borne vibration through a wall bracket is a common cause of complaint and is not captured by the airborne calculation. And a position that puts the fan discharge away from the nearest window rather than towards it.

Illustrative example: a 1930s semi with a 1.1m wide side passage and the neighbour's kitchen window 3.2m from the proposed unit position. The calculation fails against the standard because of the two reflecting surfaces. Relocating the unit to the rear garden, 6m from the nearest neighbouring window with a fence rather than a wall behind it, brings the level well inside the limit, and no application is needed. The pipe run is 4m longer and the whole problem goes away.

Making the installation lawful on paper

Permitted development leaves no decision notice, so keep your own record.

Keep the completed planning standards calculation, the manufacturer's data sheet showing the declared sound power level and the unit dimensions, a scaled plan showing the position with distances to the boundary and to the nearest neighbouring habitable room windows, dated photographs after installation, the certification paperwork, and the commissioning record.

Where a sale, a mortgage or a dispute with a neighbour is possible, a Lawful Development Certificate under section 192 for proposed works, or section 191 for something already built, is the only formal confirmation that the installation is lawful. It costs a fee and takes weeks, and it is worth it where the alternative is an argument years later.

Enter your postcode on PlanScope if an application does turn out to be needed, or browse the full list of report types to see what a householder submission usually includes.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.