Heat Pump Noise Levels: How Loud Are They Really?

This guide explains how loud heat pumps actually are and why the decibel figures you'll see quoted aren't comparable with each other. It also covers what the planning rules genuinely require (37.0 dB(A) in England and Wales; 42 is the older figure, still used in Scotland and Northern Ireland), and what you can do to minimise noise.

How Loud Are Heat Pumps?

Air source heat pumps produce sound from two sources: the fan drawing air across the outdoor unit, and the compressor. Before any number means anything, though, you need to know which of two quantities it is.

Sound power vs sound pressure: the distinction that ruins most comparisons

Sound power level (LW) is a property of the machine. It's measured in a lab, it doesn't depend on where you're standing, and it's the figure MCS 020 a) tells installers to take from the product fiche, the energy label or the MCS product database. Sound pressure level (Lp) is what you'd actually hear, at a stated distance, and it falls away as you move back. Both get printed as "dB(A)" with no qualifier, which is how the same heat pump can honestly be advertised at 54 and at 46.

MCS 020 a) converts one to the other with this formula: Lp = LW + 10 x log(Q / (4 x pi x r x r)) - AB, where Q is the directivity factor, r is the distance in metres and AB is any barrier attenuation. In plain terms, for a unit sitting on the ground against nothing, a sound power level of 54 dB(A) comes out at roughly 46 dB(A) of sound pressure at 1 metre and roughly 36 dB(A) at 3 metres. Same machine, three numbers, all labelled dB(A).

The two brands we found labelling a figure sound power for their domestic ranges (Grant, and Vaillant, whose label also mentions a 3m distance) sit at 54 to 65 dB(A) (details below). If a spec sheet gives you a decibel figure without saying whether it's power or pressure, and at what distance, it tells you nothing you can compare. Ask for the sound power from the product fiche or the MCS product database instead.

Here's a rough guide to put sound pressure figures in context. These are our estimates of typical levels, and published figures for everyday sounds vary by several decibels, so read them as ballparks:

Every figure in that table is sound pressure at the listener. Decibels are logarithmic: a 10 dB increase is generally taken as roughly a doubling of how loud it sounds. A heat pump producing 50 dB(A) where you're standing is noticeably louder than a fridge at 40 dB(A), but far quieter than a normal conversation.

The Planning Rule: 37.0 dB(A), Not 42

This is the number that changed in 2025 in England and on 1 June 2026 in Wales. Under permitted development in England and Wales, an air source heat pump can go in without a planning application provided it meets the Class G conditions. One of those is complying with the MCS Planning Standards, which the permitted development orders (England's 2015 Order and, in Wales, WSI 2026/79) now define as MCS 020 a). The requirement is:

The calculated sound pressure level must be 37.0 dB(A) or lower at every assessment position.

MCS 020 a) Issue 1.1 puts it in terms: "the permitted development noise limit of 37 dB LAeq,5mins (at the assessment positions ignoring the effect of the façade)". The assessment position is defined as "a position 1m external to the centre point of any door or window to a habitable room of a neighbouring property as measured perpendicular to the plane of the door or window". A habitable room is one used for sleeping or living, so a neighbour's bathroom or utility room doesn't create an assessment position but their bedroom or living room does.

Where does 42 come from? The old MCS 020, which is still what applies in Scotland and Northern Ireland, set the limit at 42 dB(A), but that figure had an assumed 40 dB(A) of background noise baked into the calculation. MCS split the standard in March 2025 and stripped the background-noise steps out, which is why the England and Wales number is lower: on our arithmetic, 37.0 dB(A) from the heat pump on top of a 40 dB(A) background adds up to about 42. If you see 42 dB(A) quoted for an English or Welsh installation, the page is out of date.

Your MCS-certified installer runs the calculation before installation. It takes the manufacturer's sound power level, directivity and distance to each assessment position, minus any barrier attenuation, with one calculation for each assessment position that could be affected. If the answer comes out above the limit at any of them, permitted development doesn't apply and you need full planning permission. Put a unit standing on the ground in the open through the formula, and the quietest figure labelled sound power (Vaillant's 54 dB(A), whose label also mentions a 3m distance) passes about 2.8m from the window. The loudest (65 dB(A)) needs about 10m, or a barrier. In tightly packed terraces it can be a genuine constraint, which is why you want the calculation done before you commit to a unit rather than after.

What Each Manufacturer Actually Publishes

We set out to write a "quietest heat pumps" section, went to the five big manufacturers' own UK sites to check the figures, and found they don't publish the same thing. Here is what's actually published, which is a more useful thing to know than a league table built on numbers that measure different things:

Checked on grantuk.com, daikin.co.uk, vaillant.co.uk and samsung.com/uk in October 2026, and les.mitsubishielectric.co.uk in September 2026. Read that "measurement basis" column again, because it's the finding: five brands, five different things. One gives sound power properly, one gives sound pressure at an approximate distance, one gives a figure it calls sound power at a distance, one gives quiet-mode sound pressure at 3m, and one gives nothing. A "quietest heat pump" league table built from these would compare numbers that aren't comparable, so we're not making one. The one standardised figure, and the one your installer's MCS 020 a) calculation must start from, is the A-weighted sound power level, from the product fiche, the energy label or the MCS Product Directory. Ask for your exact model's figure.

The number moves between sizes in the same range: Daikin's Altherma 3 M spans 44 to 50 dBA, and in Grant's datasheet the 6kW is the loudest of its four sizes, not the 17kW. So a brand-level figure tells you nothing about the unit going on your wall; get the figure for the size you're quoted. That's one more reason to have it sized from a proper heat loss calculation (our heat pump size calculator gives you a ballpark kW to compare against a quote).

Practical Noise Reduction Measures

Siting and Positioning

Where you place the outdoor unit has the biggest impact on perceived noise. In the open, sound falls by about 6 dB for every doubling of distance (that's the MCS formula at work). Positioning the unit:

• Away from bedrooms: especially your own or your neighbours'. Placing it at the far end of the house from sleeping areas makes a significant difference to night-time disturbance.
• Away from corners: sound reflects off walls, and every extra reflecting surface within 1m raises the MCS figure, so avoid corners or tight spaces between two walls.
• Not directly beneath a window: an open window right above the unit is the closest path into the house, so aim for placement well to the side of any frequently opened window.

Anti-Vibration Mounts

Some noise from heat pumps is transmitted as vibration through the building fabric rather than as airborne sound. Anti-vibration mounts (rubber or spring isolators between the unit and its mounting pad or bracket) reduce that, and are worth asking for on any unit mounted on a wall bracket or on a pad attached to the building.

Acoustic Fencing or Barriers

MCS 020 a) actually publishes the numbers here, which is unusually helpful. Its barrier table gives a "Type 1" barrier a 10 dB credit where it completely blocks the line of sight from the top of the unit to the assessment position, 5 dB where the view is partial, and nothing at all where the unit is still in full view. Type 1 means a solid brick or masonry wall, or a solid fence at least 18mm thick, with no gaps, extending 1m or more beyond each side of the unit. A thinner solid "Type 2" fence gets 5 dB, 2.5 dB and nothing on the same three cases. So the rule of thumb is simple: a barrier only earns its keep if it genuinely interrupts the sightline between the unit and the neighbour's window, and a slatted fence or a hedge is worth zero. Specialist acoustic enclosures designed for heat pumps also exist; ask your installer whether one suits your unit.

Note: any barrier must not restrict airflow to the unit, which needs clear access to ambient air. Manufacturers publish minimum clearance distances that must be maintained.

Addressing Neighbour Concerns

If a neighbour raises concerns about your planned heat pump installation, we'd talk to them early and openly:

• Share the MCS 020 a) noise calculation with them before installation. Showing that the calculated level at their own window comes in under 37.0 dB(A) is usually more reassuring than any amount of "you won't hear it".
• Discuss siting options: if there is flexibility in where the unit is placed, involve them in finding the least intrusive location.
• Agree what happens if it bothers them afterwards: some heat pumps have a quiet mode (Samsung's, for one) that can help after installation, but it can't be used to pass the planning calculation.

Two separate things can go wrong after installation, and it's worth keeping them apart. If a neighbour complains that the installation wasn't permitted development in the first place, that's a planning matter and the council will look at the MCS 020 a) calculation. If they complain of statutory noise nuisance, that's environmental health and it's judged on its own test, not on MCS 020 a). Don't tell a neighbour that a passed calculation makes the matter closed.

Key Takeaways

• A decibel figure with no measure and no distance is meaningless. Ask whether it's sound power or sound pressure at X metres before comparing anything
• The two makers we checked that label a figure sound power (Grant, and Vaillant, whose label also mentions a 3m distance) give 54 to 65 dB(A), which is roughly 36 to 47 dB(A) of sound pressure three metres away in the open
• In England and Wales the permitted development limit is 37.0 dB(A) at the assessment position, 1 metre outside a neighbour's habitable-room door or window, under MCS 020 a). Scotland and Northern Ireland still use the older MCS 020 and its 42 dB(A) figure
• Ignore "quietest heat pump" rankings. The five big brands publish five different kinds of figure, so those rankings compare things that aren't comparable. Ask for the sound power from the product fiche or the MCS Product Directory instead
• Siting away from bedrooms, anti-vibration mounts and a barrier that actually breaks the sightline (worth up to 10 dB under MCS 020 a)) all help
• Engage neighbours early with the calculation rather than with reassurances

For a full comparison of heat pump models including efficiency and cost data, see our guide to the best heat pumps in the UK. If you are weighing up whether the overall package makes sense for your home, read our honest assessment of whether heat pumps are worth it.