Air source heat pump planning permission for a house
Class G permits most domestic heat pumps, and noise is the condition that decides it. Here is how the calculation works and when you have to apply.
Most domestic air source heat pumps go in under permitted development, and the condition that decides it is noise. Class G of Part 14 of the General Permitted Development Order 2015 permits an air source heat pump on a house subject to a set of siting limits and a requirement that the installation complies with the relevant microgeneration planning standard. Where any of those fail, air source heat pump planning permission is needed and the application is a householder one.
The noise calculation is where installations come unstuck, and it is done before the unit is ordered rather than after it is running.
The permitted development conditions
Class G covers the installation of an air source heat pump on a dwellinghouse or within its curtilage. The conditions cover the volume of the outdoor compressor unit, where it may be positioned in relation to roofs and boundaries, restrictions in conservation areas and similar designations, and a requirement to remove the equipment when it is no longer needed.
Part 14 was amended in 2024 and the limits changed, including the size threshold for the outdoor unit and the treatment of boundaries. Take the current wording from Class G on legislation.gov.uk before you rely on a figure. Installers quoting limits from a 2019 guide are still common.
The general condition also applies: the equipment must be sited, so far as practicable, to minimise its effect on the external appearance of the building and on the amenity of the area.
Noise: the MCS calculation and who checks it
Class G requires the installation to comply with the microgeneration certification planning standard for heat pumps, commonly known as MCS 020, or an equivalent standard.
The calculation works from the sound power level of the specific unit, then applies corrections for the distance to the assessment position, the effect of nearby reflective surfaces and any barrier between the unit and the receptor. The assessment position is a window or door of a habitable room at a neighbouring property, and the resulting sound pressure level must not exceed 42 dB(A).
Three practical consequences follow.
The unit model matters, because two pumps of the same output can differ by several decibels. Position matters more, because doubling the distance to the neighbouring window buys more than most acoustic accessories will. And a location in a corner between two walls is the worst case, since the reflections add.
Nobody checks the calculation at the time. It is produced by the installer, kept with the paperwork and only ever examined if a neighbour complains or a buyer's solicitor asks. Keep it.
Siting near boundaries and on walls facing a highway
Beyond the noise standard, the restrictions that matter in practice are about visibility and proximity.
| Situation | What to check |
|---|---|
| Conservation area or similar designation | Restrictions on installation on a wall or roof fronting a highway |
| Listed building | Permitted development does not apply, and listed building consent is needed |
| Flat roof position | Limits on proximity to the edge and to boundaries |
| Front garden or forecourt | Visibility from the street, and the amenity condition in Class G |
| Article 4 direction | Rights may be removed entirely for the area |
A pump on a side elevation set behind a boundary wall is almost always the easiest position to defend, both for planning and for noise. A pump on a front elevation of a house in a conservation area is the hardest.
Think about servicing access and airflow at the same time. A unit wedged against a fence with 200 mm of clearance will short-cycle its own cold discharge air, run less efficiently and need the fence panel removed every time an engineer visits. The manufacturer's clearance dimensions are as much a siting constraint as the planning limits are.
Listed buildings, conservation areas and flats
Listed building consent is required for works affecting the character of a listed building, and installing a heat pump with pipework penetrating an external wall will normally engage it. Carrying out the works without consent is a criminal offence, so the sequence is consent first, installation afterwards.
In a conservation area, the Class G restrictions on highway-facing positions apply, and an Article 4 direction can remove the rights altogether. Where an application is needed, a Heritage Statement that explains the position chosen, the alternatives rejected and the reversibility of the fixings does most of the work.
Flats are a separate question. Householder rights do not apply to flats, the position under Part 14 needs checking against the current text, and in any event the external wall or roof normally belongs to the freeholder, whose consent is a private matter the council will not resolve.
When you must apply, and what to include
Apply where the unit exceeds the size limit, sits in a restricted position, fails the noise standard at the assessment position, or where the rights have been removed.
A householder application should include a site plan with the unit position and the distance to neighbouring windows marked, an elevation showing it, the manufacturer's data with the sound power level, the noise calculation, and a short statement on why the position was chosen. Where the acoustic case is tight, a Noise Impact Assessment from an acoustician carries considerably more weight than an installer's spreadsheet.
Neighbour complaints after installation
A pump installed under permitted development can still be a statutory nuisance under the Environmental Protection Act 1990 if it causes a genuine problem, and the environmental health team can act regardless of the planning position.
Most complaints trace to three things: a defrost cycle running at four in the morning, a unit mounted on a wall shared with a neighbour's bedroom so vibration transmits through the structure, or a position in a narrow passage between two houses where the sound reflects. Anti-vibration mounts, a change of position and a limit on night-time operation resolve most of them, and doing that quickly costs far less than defending an abatement notice.
Talk to the neighbour before the unit arrives. A five-minute conversation about where it is going, and an offer to move it if the noise turns out to be a problem, prevents most of the disputes that end up with environmental health. Once a complaint is on file the conversation is much harder.
Recording compliance for a future sale
Keep the MCS certificate, the noise calculation, the manufacturer's data sheet and dated photographs of the installed position in one file.
Where the case was marginal, a Lawful Development Certificate under section 192 of the Town and Country Planning Act 1990 confirms the works are lawful, and it is the only formal way to do so. It takes about eight weeks and carries a fee, which is modest set against a sale falling through at the enquiries stage. The same reasoning applies to other householder equipment where permitted development limits are close, such as the plant serving a swimming pool, indoors or outdoors.
Check what a householder application needs before you submit. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
Do I need planning permission for an air source heat pump?
Usually not. Class G of Part 14 of the General Permitted Development Order 2015 permits a heat pump on a house subject to siting limits, a size limit on the outdoor unit and compliance with the microgeneration planning standard. Permission is needed if any of those fail or if rights have been removed by an Article 4 direction.
What is the noise limit for a domestic heat pump?
The microgeneration planning standard requires the calculated sound pressure level at the assessment position, a window or door of a habitable room at a neighbouring property, not to exceed 42 dB(A). The calculation starts from the unit's sound power level and applies corrections for distance, reflective surfaces and any barrier.
Who checks the noise calculation?
Nobody, at the time. The installer produces it and keeps it with the paperwork under the certification scheme. It is examined only if a neighbour complains or a buyer's solicitor asks during a sale. Keep the calculation, the certificate and the manufacturer's data together in one file from the start.
Can I install a heat pump on a listed building?
Permitted development does not apply, and listed building consent is required for works affecting the character of the building, which pipework penetrating an external wall normally will. Carrying out the works without consent is a criminal offence, so obtain consent before installation. Positions on rear elevations with reversible fixings are the easiest to justify.
What if my neighbour complains about noise afterwards?
A pump installed under permitted development can still amount to a statutory nuisance under the Environmental Protection Act 1990, and environmental health can act. Most complaints trace to defrost cycles at night, vibration through a shared wall, or a unit in a narrow passage. Anti-vibration mounts and repositioning resolve the majority.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.