Heat pump permitted development or a planning application

An air source heat pump permitted development installation stands or falls on two questions: does the calculated noise level at the neighbour's window come in at or below 42 dB(A), and is there a position for the unit that the right actually covers. Almost every case that needs a planning application fails one of those, and the size of the unit is rarely the problem.

The right is in Schedule 2 Part 14 of the General Permitted Development Order 2015, and it is conditional. Conditional rights are not the same as unconditional ones: fail a condition and the installation is unauthorised development, even though nobody applied for anything and nobody told you.

The limits in the permitted development right

The right covers installation of an air source heat pump on a dwellinghouse or a block of flats, or within the curtilage, subject to a set of limitations and conditions.

Four conditions matter in practice. The pump must be used solely for heating purposes. It must comply with the microgeneration planning standards. It must be sited so as to minimise its effect on the external appearance of the building and on the amenity of the area. And it must be removed as soon as reasonably practicable when no longer needed.

The dimensional and siting limits, including the size of the outdoor unit and its position relative to boundaries, have been amended since the right was introduced. So read the current consolidated text of Class G rather than a summary written before the last change, and check whether an Article 4 direction applies locally.

One more limitation catches people. Where a wind turbine already stands on the building or within its curtilage, the heat pump right is not available.

Noise conditions and how they are met

This is the condition that does the work, and it is a calculation rather than a measurement.

The microgeneration planning standards set out a procedure: take the sound power level of the specific unit from the manufacturer's data, apply the distance to the assessment position, apply factors for reflective surfaces and any barrier, and compare the result against 42 dB(A). The assessment position is one metre from a habitable room window or door of neighbouring premises.

Four things move the answer.

• The unit selected, because sound power levels differ substantially between models of similar output.
• The distance to the nearest neighbouring habitable room opening.
• The number of hard surfaces close to the unit, since a pump in a corner between two walls is reflecting sound in two directions.
• Whether a barrier is present, and whether it is solid, high enough and close enough to count.

Get the calculation done at design stage on the specific model, in writing, and keep it. An installer who says it will be fine has not done a calculation, and a courtyard or a narrow side passage between two terraced houses is exactly where the arithmetic fails.

Where the calculation cannot be met, a planning application is the route, and the council will want a proper acoustic assessment rather than the microgeneration sheet. That is where a Noise Impact Assessment prepared to a recognised methodology becomes the supporting document.

Conservation areas and listed buildings

Designation narrows the right and adds a separate consent regime, in the same way it does for other external fixings.

In a conservation area or World Heritage Site the right does not cover installation on a wall or roof fronting a highway, nor installation on a building within the curtilage. So the workable positions are rear and side elevations out of public view, and a corner plot with two highway frontages can be very awkward.

Listing is a separate question. Permitted development rights are about planning permission, and listed building consent is required for works affecting the character of a listed building as one of special architectural or historic interest. Bolting a condenser to a historic elevation, cutting a 60 mm pipe penetration through ashlar and routing a condensate drain are all such works. Treat consent as necessary and design the route accordingly.

Flats and shared walls

The right extends to blocks of flats, which surprises people, and it is not the end of the analysis.

A leaseholder almost always needs the freeholder's consent for an external alteration, and many leases prohibit fixings to the structure outright. That is a private law question the planning system does not touch, and it is the more common obstacle.

Then there is the party wall. A unit fixed to a wall shared with a neighbour transmits vibration through the structure, which the airborne noise calculation does not capture. Anti-vibration mounts and a freestanding base rather than a wall bracket are the practical answers, and on a shared wall the freestanding option is worth the extra space it takes.

Where a block is converting several flats, one shared arrangement designed properly beats six individual units bolted to whichever elevation was convenient.

Where an application is unavoidable

Six situations, and none of them is a reason to abandon the project.

The calculated level exceeds 42 dB(A) and no reasonable relocation or barrier brings it down. The only viable position fronts a highway in a conservation area. An Article 4 direction has removed the right. More than one unit is needed. The building is not a dwellinghouse or block of flats, so Part 14 does not apply. Or the unit will serve something other than heating.

A householder application for a heat pump is a modest submission: a location plan, a site plan showing the unit position with dimensions, an elevation, the manufacturer's data sheet, and the acoustic assessment. A short Planning Statement addressing amenity and the relevant development plan policies is usually enough on top of that.

As an illustrative example, a mid-terrace house with a 4 m rear yard, neighbouring kitchen windows 2.5 m away on both sides and brick walls on three sides is a case where the calculation is likely to fail on any unit and where a planning application with an acoustic enclosure is the realistic path. A detached house with 8 m to the nearest neighbouring window is a case where nobody needs to apply for anything.

If an application is refused, the fast-track route applies to householder refusals, and knowing which procedure you are in matters, so the householder appeal route is worth checking before you decide whether to appeal or revise.

Evidence to keep on file

Five documents, in one folder, kept for as long as you own the house.

The microgeneration certificate for the installation. The sound calculation sheet showing the model, the distances and the result. The manufacturer's technical data including the sound power level. The commissioning record. And dated photographs of the installed position with a tape measure in shot showing the distance to the boundary and to the nearest neighbouring opening.

That folder answers a conveyancing enquiry, an environmental health enquiry and a planning enforcement enquiry. Without it, an owner three years later has no way of demonstrating that a condition of the right was satisfied on the day.

Where the pump forms part of a wider retrofit or a new build, the figures should be consistent with the Energy Statement, particularly the seasonal efficiency assumed and the electrical load, because a planning submission that quotes two different performance figures invites a question.

Confirming lawfulness

Where certainty matters, apply for a lawful development certificate for proposed use or development. It is the only formal route to confirmation, it puts the council's view on the record, and it produces a document with legal standing.

Do it before installation rather than after. A certificate for proposed development is decided on the design; a certificate for existing development has to be argued on what was built. And permitted development status does not displace environmental protection law, so a unit that becomes a statutory nuisance can still be dealt with by the council's environmental health team.

Enter your postcode on PlanScope to see which documents an application for external plant at your property would need.

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.