Heat Pump Noise Levels: How Loud Are They Really?

Heat Pump Noise Levels UK: What to Expect and How to Manage It

Noise is one of the most common concerns among homeowners considering a heat pump, and one of the most common reasons neighbours object. This guide explains how loud heat pumps actually are, why the decibel figures you'll see quoted aren't comparable with each other, what the planning rules genuinely require (37.0 dB(A), not the 42 you'll read almost everywhere), 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 (L_W) 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 holds for every certified product on its Product Directory. Sound pressure level (L_p) 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: L_p = L_W + 10·log(Q ÷ 4πr²) − A_B, where Q is the directivity factor, r is the distance in metres and A_B 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 37 dB(A) at 3 metres. Same machine, three numbers, all labelled dB(A).

Mainstream domestic units sit in a band of roughly 45 to 56 dB(A) sound power. 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 MCS Product Directory entry instead.

To put sound pressure figures in context:

Every figure in that table is sound pressure at the listener. Decibels are logarithmic, so a 10 dB increase is roughly a doubling of perceived loudness. 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 most guides still get wrong, including ones updated this year. Under permitted development in England and Wales, an air source heat pump can go in without a planning application provided the installation complies with the MCS Planning Standards, which the Town and Country Planning (General Permitted Development) (England) Order 2015 now defines 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 L_Aeq,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 without the rule actually being tougher in practice. 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: manufacturer's sound power level, directivity, distance to each assessment position, minus any barrier attenuation. One table per 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. Most modern heat pumps at a sensible distance from the boundary pass. 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 "the quietest heat pumps" section that every roundup has, went to the five big manufacturers' own UK sites in September 2026 to check the figures, and couldn't. Here is what's actually published, which is a more useful thing to know than a league table built on numbers nobody will stand behind:

Checked on vaillant.co.uk, les.mitsubishielectric.co.uk, daikin.co.uk, samsung.com/uk and grantuk.com in September 2026. Read that "measurement basis" column again, because it's the finding: of five mainstream brands, three publish no consumer-facing noise figure at all, one publishes two different numbers without saying what either one is, and only Daikin tells you the quantity and roughly the distance. Every "quietest heat pump 2026" ranking you'll read is therefore built on numbers traded between comparison sites rather than taken off a datasheet, and we're not adding another. The one standardised figure, and the one your installer's MCS 020 a) calculation must start from, is the A-weighted sound power level MCS holds per certified product on the MCS Product Directory. Ask for your exact model's entry, and ask for the completed sound calculation for your site. Those two documents settle it; a brochure decibel doesn't.

Bigger units are louder than smaller ones in the same range, which is another reason right-sizing through a proper heat loss calculation matters: an oversized heat pump is noisier as well as less efficient and shorter-lived. Daikin's published 44 to 50 dBA spread across a single model line is a good illustration of how much the output rating moves the number, and of why a brand-level figure tells you nothing about the unit going on your wall.

Practical Noise Reduction Measures

Siting and Positioning

Where you place the outdoor unit has the biggest impact on perceived noise. As a rule of thumb, sound reduces by approximately 6 dB for every doubling of distance. 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, so avoid positioning in corners or against two walls where sound can build up.
• Not directly beneath a window: noise travels upward into open windows, so aim for placement at least 1 metre 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 placed between the unit and its mounting pad) cost £50–£150 and can reduce transmitted vibration significantly. They are a worthwhile addition for any unit mounted on a wall bracket or concrete pad attached to the building.

Acoustic Fencing or Barriers

MCS 020 a) actually publishes the numbers here, which is unusually helpful. Its barrier attenuation table gives a solid, heavy barrier ("Type 1") a 10 dB credit where it completely blocks the line of sight from 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. A lighter "Type 2" barrier 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 you can see through is worth zero. Solid timber or masonry, tall enough to break the line of sight. Specialist acoustic enclosures designed for heat pumps cost £300–£800 fitted.

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, the best approach is to engage early and transparently:

• 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.
• Offer to monitor noise post-installation: modern heat pumps can be operated in a night quiet mode (typically 3–6 dB quieter but with some efficiency reduction) if noise proves to be an issue after installation.

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): passing the planning calculation is not an automatic defence. In practice, provided the calculation was done properly and the unit is operating within specification, complaints are rarely upheld, but 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
• Mainstream units sit around 45 to 56 dB(A) sound power, which is roughly 37 to 48 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. Three of the five big brands publish no consumer-facing noise figure on their UK sites at all, so those rankings aren't built on anything. Ask for the MCS Product Directory entry 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.