Assessing a heat pump after a neighbour complains

When a neighbour complains about an air source heat pump that is already installed, two questions have to be answered separately. Was the installation permitted development under Part 14 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, which depends on whether the noise calculation was done correctly at the time. And is the unit causing a statutory nuisance under the Environmental Protection Act 1990, which is a different test applied by environmental health. A heat pump noise complaint can fail one and pass the other.

Work through them in order, honestly, because the worst outcome is defending a calculation that turns out to have been done wrong.

Establishing whether the installation was permitted development

Part 14 permits the installation of an air source heat pump on domestic premises subject to conditions, and one of those conditions is that the installation complies with the relevant planning standard for microgeneration, or an equivalent standard.

The other conditions cover the physical installation. There are limits on the size of the outdoor unit, restrictions on siting relative to the roof, and restrictions where the property is listed, in a conservation area or in a World Heritage Site. The unit must be used solely for heating and must be removed as soon as reasonably practicable when no longer needed.

Several of these were relaxed in 2024, including the volume limit and a former requirement about distance from the boundary, so check the current text of the Order rather than a summary from before then. Whether the installation was permitted development is judged against the rules as they stood on the date it was installed, which is why the installation date matters.

If any condition was not met, the installation was not permitted development, and it is unauthorised development from the outset. That is not a disaster, but it does mean the council can require an application.

Rerunning the planning standard calculation honestly

The microgeneration planning standard works by predicting the sound pressure level at an assessment position, which is one metre from the nearest habitable room window of a neighbouring property, and comparing it with a fixed limit of 42 dB(A).

Redo it properly with the actual installed arrangement. Four inputs decide the answer.

• The declared sound power level of the unit, taken at maximum rated output rather than at a favourable part load figure.
• The straight line distance from the unit to the assessment position, measured, not estimated from a drawing.
• Reflections, adding for each hard surface adjacent to the unit, since a pump in a corner between two walls is louder at the receiver than the same pump in open air.
• Any barrier between the unit and the assessment position, and only where it is solid and breaks the line of sight completely.

The most common errors are using the part load sound power figure, ignoring a second reflecting surface, and picking an assessment position at the neighbour's kitchen when their bedroom window is closer. Any one of them can move the result by several decibels.

If the honest recalculation exceeds the limit, the installation was not permitted development. Say so internally and move to the retrospective route rather than arguing about it, because the council will do the same calculation.

What an environmental health investigation looks at

Environmental health is not applying the microgeneration standard. Officers investigate whether the noise amounts to a statutory nuisance, and that is a judgement about the effect on the neighbouring occupier.

Officers typically ask the complainant to keep a log of dates, times and durations, then attend to witness the noise themselves, sometimes at night. They may install unattended monitoring equipment in the complainant's property for a period.

What they weigh includes the level of the noise relative to the background, its character, the time of day, how long it lasts and how often it happens, and the character of the area. Tonality matters a great deal. A steady hum with a distinct pitch is far more likely to be judged a nuisance than a broadband whoosh at the same level, and defrost cycles that start and stop through a winter night are worse than continuous running.

Statutory nuisance and how it differs from the planning test

The two tests can give opposite answers, and understanding why prevents a lot of wasted argument.

A unit that predicts 41 dB(A) may still be a nuisance if it is tonal, runs at night and sits in a quiet rural garden. A unit predicting 44 dB(A) beside a main road may never attract a complaint at all.

If the council is satisfied a statutory nuisance exists, it must serve an abatement notice, and failing to comply with the notice is an offence. A neighbour can also take their own action in the magistrates' court under the Act without involving the council.

Neither route depends on whether the installation was lawful development. Compliance with the planning standard is not a defence to a nuisance.

Physical fixes that work and those that do not

Deal with the acoustics before the paperwork, because a quiet unit ends the complaint whatever the legal position.

What works. Moving the unit away from the boundary and out of a reflecting corner. A solid, imperforate acoustic barrier close to the unit, with enough mass and enough height to break line of sight to the receiver, while leaving the manufacturer's clearances for airflow. Anti-vibration mounts and a flexible pipe connection, since much of what neighbours describe as a hum is vibration transmitted through the wall or the slab. Running the unit at lower fan speed for longer, which usually means a correctly sized system rather than an oversized one working hard. A night setback where the heating strategy allows it.

What does not work. Planting and shrubs, which have no useful acoustic effect at these frequencies. A close boarded fence with gaps, which lets sound straight through. Boxing the unit in without acoustic design, which restricts airflow, makes the compressor work harder and often makes it louder. Moving the unit to a first floor wall, which raises it towards bedroom windows.

Where the arrangement is complicated or the dispute has hardened, a short assessment from a qualified acoustician measuring the actual level is worth more than another round of predictions. A Noise Impact Assessment covering measured levels, the character of the sound and a mitigation scheme gives both the council and the neighbour something concrete.

Applying retrospectively and what the council can require

Where the installation was not permitted development, the routes are a retrospective planning application or, if you believe it did comply, a certificate of lawfulness.

A retrospective application is decided on planning merits, and the council will consider amenity, the effect on the neighbour and any mitigation you propose. Submitting it with the mitigation already installed, and with measurements showing what it achieves, is far stronger than submitting it as an argument.

If permission is refused, the council can serve an enforcement notice requiring removal or alteration, with a compliance period and a right of appeal. Separately, environmental health can serve an abatement notice at any point, and that is the faster of the two routes from the neighbour's point of view.

A short Planning Statement setting out the installation history, the recalculated prediction, the measured levels and the mitigation is the right supporting document. Keep it factual.

Records to keep while resolving it

Assemble these now, whatever the eventual outcome.

1. The installation date, installer details and any microgeneration certification.
2. The original planning standard calculation, if one was done, with its inputs.
3. The manufacturer's technical data showing the declared sound power level and the conditions it applies to.
4. A measured drawing showing the unit, the boundary and the nearest habitable room windows of neighbouring properties.
5. A dated record of every change made, with photographs.
6. Correspondence with the neighbour, kept civil and factual.

That last one matters more than it looks. Most of these disputes are resolved by an owner who responds quickly and visibly, and hardened by one who does not.

This is general guidance, not legal advice. Permitted development conditions and noise standards change, so check the current position with your local planning authority's planning and environmental health teams, and take advice from a qualified acoustician, before relying on it.

If you need to put a retrospective case together, browse the report types by category and start from the situation rather than the form.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.