How noisy is a heat pump? UK rules and planning

How noisy is a heat pump in practice: quiet enough that the planning rules in England cap it at 37 dB(A) measured at a neighbour's window, which is roughly what a fridge makes across a kitchen. That cap is not advice. It is the condition the installation has to meet to be permitted development at all.

This explains where that number comes from, how the assessment is done, and what actually determines where the outdoor unit ends up on your house. The units we fit are on the air source heat pumps page.

The rules, in short

The planning limit in England is 37 dB(A) at the assessment position, which is one metre from the nearest habitable room window or door of a neighbouring property.
The calculation is set out in MCS 020 a). Compliance with it is a condition of permitted development.
The installer takes the unit's sound power figure from the datasheet and applies distance, reflection and barrier corrections to predict the level at each assessment position.
Pass at every position and the job is permitted development. Fail at any one and it needs a full planning application.
The outdoor unit can be no more than 1.5 cubic metres on a house, or 0.6 cubic metres on a block of flats.
Listed buildings and scheduled monuments are excluded. Conservation areas restrict walls and roof slopes facing a highway.

How noisy is a heat pump in everyday terms?

Standing next to a running unit you hear a fan and a low hum from the compressor. It is a steadier, lower sound than an air conditioning condenser and much steadier than a fridge cycling on and off.

The figure that matters is not the one you hear standing over it, though. It is the level at your neighbour's window, and sound falls away quickly with distance. A unit that is clearly audible from a metre away is often inaudible from ten, particularly with a fence or a wall between.

Two numbers on a datasheet get confused, and it is worth knowing which is which. Sound power is the total the unit emits and is the figure the calculation starts from. Sound pressure is what you would measure at a stated distance, and manufacturers quote it at different distances, which makes brochure comparisons close to useless. Ask for the sound power level.

What are the heat pump noise regulations in the UK?

For domestic installs in England the rules sit inside permitted development, and they point at a single standard: MCS 020 a).

Development is permitted only if the installation complies with that standard. The sound calculation has to show 37 dB(A) or lower at the assessment position of the nearest noise-sensitive premises. The assessment position is external, one metre from the neighbour's closest habitable room window or door.

The installer runs that calculation before the job is designed, not after. It takes the manufacturer's sound power figure and applies corrections for distance, for reflections off walls and hard surfaces, and for any barrier between the unit and the assessment position. The output is a predicted sound pressure level at every relevant position.

At or below 37 dB(A) everywhere, the install is permitted development. Above it anywhere, you need a full planning application, which is not the end of the world but adds weeks and a fee.

Since May 2025 the rules also removed the old one metre boundary restriction and raised the size limit, and they now allow air-to-air units, which is why fixed air conditioning can also be permitted development.

Do I need heat pump planning permission in the UK?

Usually not, provided the conditions are met.

The installation must comply with MCS 020 a). The outdoor compressor unit including its housing must not exceed 1.5 cubic metres on a house, or 0.6 cubic metres on a block of flats. On a detached house the first two heat pumps are permitted development; on anything else, the first one.

Permitted development does not apply inside the curtilage of a listed building or on a scheduled monument. In a conservation area there are further restrictions on installations on walls or roof slopes that front a highway.

Flats and maisonettes have their own conditions, and a property with an existing permitted development array may have used up its allowance. We check all of this at the survey and tell you before anything is ordered.

Is a heat pump noisy at night?

This is the question that really sits behind the others, because heating runs overnight and bedrooms are usually at the back of the house where the unit went.

Three things matter here. A heat pump left at a steady temperature runs at low fan speed for long periods, which is quieter than a unit cycling hard to recover from a deep setback, so the old boiler habit of turning everything off at eleven works against you. Defrost cycles, which clear frost off the outdoor coil in cold damp weather, are the loudest moments and last a few minutes. And an outdoor unit mounted on a house wall can transmit vibration into the structure, which is why we prefer a ground-mounted base with anti-vibration feet wherever there is room.

The 37 dB(A) assessment is done against a habitable room window, and bedrooms count. If the only place a unit will pass is the front of the house, that is where it goes.

What makes one unit louder than another?

Size, mostly. A larger unit moving more air makes more noise at full output, which is another reason an oversized heat pump is a bad heat pump.

Fan design and casing matter too, and most manufacturers now publish a quiet mode that reduces fan speed overnight at the cost of some output. Useful, but it should not be the thing that gets a marginal position over the line. If a position only passes in quiet mode, pick a better position.

A worked example: a semi in Kimberworth

Three-bed semi, neighbour's kitchen window at the side, the obvious spot for the unit is the side passage.

The MCS 020 a) calculation on that position came back above the limit, because the passage is narrow and both walls reflect sound straight at the window. Moving the unit to the rear corner of the house, onto a ground base with the fence acting as a barrier, brought the predicted level under 37 dB(A) with room to spare. It added a few metres of pipe run and nothing else.

That is a normal outcome. Most failures are a siting problem, not a product problem.

What I would do about a neighbour

Tell them before the scaffold and the van turn up, not after.

I have watched jobs where the neighbour found out when the groundworks started and objected on principle, and jobs where somebody knocked on the door first, showed them the noise assessment, and the whole thing passed without a word. The second approach costs five minutes.

If you are ever on the receiving end of a noisy unit next door, the route is your council's environmental health team, and the first thing they will ask for is the installation's sound assessment. A proper installer will have one on file.

Before you worry about the neighbours

Is my house suitable for a heat pump covers heat loss, radiators and where the cylinder goes, and heat pump cost after the grant covers the money.

If you want the noise assessment done for your own house before you commit to anything, Get a quote with your postcode and we will do it as part of the survey. Or ring 01709 278248.