Heat pump noise and the permitted development condition

Most domestic air source heat pumps in England go in without a planning application, under Class G of Part 14 of the General Permitted Development Order 2015. That permission is not unconditional. One of the conditions is about noise, and it is the one that catches people out, because it has to be satisfied before installation rather than argued about afterwards.

The noise condition works by reference to the Microgeneration Certification Scheme planning standard, MCS 020. In outline, the installer calculates the sound level the unit will produce at the nearest assessment position on a neighbouring property, and the installation only benefits from permitted development if that figure comes in at or below 42 dB(A). Miss it, and you need planning permission.

The permitted development class and its noise condition

Part 14 covers renewable energy installations on domestic premises, and Class G deals with air source heat pumps. The conditions attached to it have included limits on the size of the unit, restrictions on where it can sit in relation to the boundary and the roof, a requirement that it be used solely for heating purposes, and the MCS 020 compliance requirement.

Part 14 has been amended more than once since 2015, including changes intended to make heat pump installation easier, so the limits that applied to a job two years ago may not be the limits that apply today. Read the current consolidated text of Schedule 2 Part 14 on legislation.gov.uk, or ask the installer to show you which version they worked to. An installer quoting a limit from memory is not evidence of anything.

Removal of the equipment when it is no longer needed for microgeneration is also a condition, which matters when a property changes hands.

How the calculation method works

MCS 020 is a calculation, not a measurement. It starts from the sound power level of the specific heat pump model, taken from the manufacturer's data at the rating condition, and works out the sound pressure level at the assessment position.

The assessment position is the point that matters most and the one most often got wrong. It is taken at a neighbouring property, at a habitable room window or door, rather than at the boundary or at the installing property's own window. Where several neighbours are affected, the worst case governs.

The calculation then accounts for the distance from the unit to that position, and for the effect of the surrounding surfaces. A unit sitting in a corner between two walls gets a correction that increases the result, because sound reflects. A solid barrier between the unit and the neighbour gives a reduction, provided it blocks the line of sight properly and is built of a material with enough mass.

The output is a single figure at the assessment position. Against the 42 dB(A) limit, there is no margin for judgement. The installer should give you the completed worksheet, and you should keep it.

Siting decisions that change the result

Siting is the variable you control. Small moves make a real difference to the calculated figure, and thinking about them before the unit is ordered is far easier than dealing with a complaint later.

• Distance from the neighbouring window is the strongest single factor. Moving the unit a few metres further away changes the result more than any acoustic accessory.
• Corners and recesses increase the level because of reflection. An open wall face is better than an alcove.
• A masonry wall or a close-boarded fence between the unit and the neighbour helps if it interrupts the line of sight. A slatted screen with gaps does not.
• Mounting on a wall transmits vibration into the building structure. A ground-mounted unit on its own base, with anti-vibration mounts, avoids a whole category of complaint about noise heard indoors.
• Point the fan discharge away from the neighbour and away from a facing wall where possible.

Where a garden is narrow and the neighbouring windows are close, the honest answer is sometimes that no compliant position exists. Better to know that before the equipment arrives.

When the condition cannot be met

Failing the 42 dB(A) test does not mean the heat pump cannot be installed. It means the installation falls outside Class G and needs a planning application, which is a householder application determined against the local plan's amenity policies.

For that application, the council will want an acoustic assessment rather than an MCS 020 worksheet. That normally means an assessment following BS 4142:2014+A1:2019, which compares the specific sound level of the plant with the background sound level at the nearest noise-sensitive property and considers the character of the sound. A noise impact assessment prepared on that basis, with measured background levels rather than assumed ones, is what an environmental health officer will look for.

Expect conditions if permission is granted. Limits on the sound level at the boundary, a requirement to install the specific model assessed, and sometimes restricted operating hours for a defrost cycle or a boost mode.

Designated land and listed buildings

Permitted development rights are narrower on designated land, meaning conservation areas, National Parks, National Landscapes and World Heritage Sites, and the restrictions in Part 14 for those areas are about visibility as well as noise. A unit on a wall or roof fronting a highway is the usual sticking point.

Listed buildings are a separate matter entirely. Listed building consent is required for works affecting the character of a listed building, including fixing plant to an external wall, running pipework through the fabric or installing a unit within the curtilage where it affects the setting. Permitted development rights under Part 14 do not remove that requirement, and carrying out works to a listed building without consent is a criminal offence rather than a planning breach.

Article 4 directions can also remove Part 14 rights in a particular area. Check the council's own mapping before assuming the right exists.

Noise complaints after installation

A compliant installation can still generate a complaint, and the route the complaint takes is environmental health rather than planning enforcement. Under section 79 of the Environmental Protection Act 1990, noise from premises that is prejudicial to health or a nuisance is a statutory nuisance, and the council has a duty to investigate. If it is satisfied that a nuisance exists, it must serve an abatement notice.

Statutory nuisance is judged on the effect at the receiving property rather than on compliance with a planning standard, so meeting MCS 020 is helpful evidence but not a defence in itself. The complaints that succeed usually involve tonal or low-frequency noise at night, or a unit that has developed a fault, rather than steady operation at the design level.

Most cases are resolved before that stage by adjusting the operating schedule, servicing the unit, adding anti-vibration mounts or building a barrier. The neighbour conversation before installation tends to prevent more problems than any of those.

Evidence to keep on file

Keep a folder, because the person who needs it will be your buyer's conveyancer in six years' time.

1. The completed MCS 020 calculation, showing the model, the sound power level used, the assessment position and the result.
2. The manufacturer's data sheet for the exact model installed.
3. The MCS installation certificate.
4. A dated photograph showing the position of the unit relative to the boundary and the neighbouring windows.
5. Where any doubt exists, a lawful development certificate from the council under section 192 of the Town and Country Planning Act 1990 confirming the installation is permitted development.

That last one is the only formal way to confirm the works are lawful, and it costs a fraction of what an enforcement dispute or a failed sale costs. Councils generally deal with them as a paper exercise on the documents you already hold.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and check the current text of the Order because Part 14 changes.

PlanScope drafts noise and supporting documents structured to UK planning policy, with site-specific facts flagged for confirmation, and acoustic work of this kind should be checked by a suitably qualified professional. Enter your postcode to see which reports your site needs. Reports should be reviewed before submission, and we do not guarantee planning approval.