Round after round of doorstep chats about that low mechanical hum rarely change anything, because the person who owns the heat pump or air conditioning unit usually isn’t the one who decides where it sits. That decision was made months earlier by an installer following a noise calculation, and the only thing that can force a rethink now is a formal noise complaint lodged with the local council’s environmental health team, not another awkward conversation over the garden fence.
Key takeaways
- The 1-metre boundary rule you thought applied was quietly scrapped in May 2025—but the noise limit of 42 dB still stands
- A council environmental health officer with a decibel meter carries far more weight than a neighbour’s complaint at the door
- New standards tightened the noise ceiling from 42 dB down to 37 dB, meaning older installations could now fail if reassessed
Why the friendly chat so often goes nowhere
There’s nothing wrong with a polite word first, and plenty of neighbours genuinely don’t realise their unit is audible three gardens away at 2am. But once a heat pump or air con condenser has been installed under what’s called permitted development, the homeowner has, in most cases, already met the legal noise requirement on paper. Telling them it’s “too loud” doesn’t carry any weight against a document that says otherwise.
Under the Microgeneration Certification Scheme, which sets the standards for permitted development, a heat pump must not exceed a noise level of 42 dB (decibels) when measured from a neighbour’s property boundary, roughly the equivalent of a quiet refrigerator’s hum. That figure comes from a standard called MCS 020, and it sets out how the installer must calculate the predicted noise level at the nearest neighbour’s habitable room, what allowances apply for fencing and barriers, and the 42 dB(A) ceiling at 1m from that window. If the paperwork says the unit passes, your neighbour has every right to shrug off a complaint made at the door. What they can’t shrug off is a council officer with a decibel meter.
The boundary rule everyone assumes still applies
A lot of the frustration around units “against the fence” comes from an old rule of thumb that no longer holds in England. A previous requirement that the heat pump had to be at least 1 metre away from the property boundary was removed in May 2025 as it was felt to be blocking access to heat pumps for many households, particularly those living in terraced properties who would find it difficult to comply with the regulations. So a unit hard up against a shared fence isn’t automatically unlawful, however much it might feel that way when you’re trying to sleep.
What hasn’t disappeared is the sound limit itself. The distance restriction has been withdrawn, but the sound level limitation is still in force, and homeowners are still required to ensure their systems meet the 42 dB sound restriction. Wales, incidentally, hasn’t relaxed things at all: Wales still requires a 3 metre boundary distance for air source heat pumps, which is why permitted development is harder west of the Severn. If you’re in Cardiff rather than Croydon, the maths your neighbour’s installer should have done looks quite different.
The one request that actually moves things
Here’s the bit most people skip. Rather than repeating yourself at the door, you report the noise to your council’s environmental health service as a possible statutory nuisance. If a neighbour noise complaint is made, the local council’s environmental health officers will investigate, typically measuring noise levels at the complainant’s property and comparing them against the statutory heat pump noise limit. That’s the request that matters: it triggers an independent measurement, not a debate about who’s being unreasonable.
The outcome genuinely can go either way, and that’s worth being honest about. If the installation was done properly, used the MCS heat pump noise calculator, and stays below 42 decibels at the boundary, the homeowner is almost certainly protected, because the assessment provides documented evidence of compliance. Ask for a copy of that MCS 020 paperwork before you go any further; a good neighbour, and a good installer, should have it on file. But if the figures don’t stack up, or the unit is running louder than it was ever assessed to, councils have real teeth. Councils may investigate and issue enforcement notices if a unit is noisy. An enforcement notice can require the unit to be moved, baffled, serviced, or in stubborn cases removed altogether, which is exactly the “stays against the fence or not” decision the request sets in motion.
It’s worth knowing the standard itself has been tightening. One of the headline shifts under the updated MCS-020(a) standard is a reduction in the maximum allowable noise limit for neighbour-sensitive installations, down from 42 dB to 37 dB LAeq for 5-minute measurements. That’s not a trivial adjustment; that difference may seem small, but in decibel terms, it translates to more than a halving of perceived sound energy. An install signed off a few years ago under the older, looser figure might genuinely fail if reassessed today, which is exactly the kind of detail an environmental health officer will check.
What to have ready before you pick up the phone
Before ringing the council, jot down when the noise happens, roughly how long it lasts, and whether it’s worse on cold nights (heat pumps typically work harder, and louder, in freezing conditions). A short diary of dates and times strengthens your case enormously and helps the council decide whether to schedule a proper noise survey rather than a quick drive-by. It costs nothing beyond a bit of patience, and unlike another knock on the door, it produces an answer that actually settles the argument.
One quirk worth remembering: distance does most of the heavy lifting in these calculations, so a small change on your neighbour’s part can go a long way. Every doubling of distance reduces sound by approximately 6 dB, and simply moving a unit further from a boundary can reduce perceived noise at the boundary by 10 dB or more compared to placing it right against a fence. Sometimes the fix isn’t an enforcement notice at all, just a friendly suggestion, backed by the council’s findings, to shift the unit eighteen inches to the left.
Sources : mcscertified.com | squote.app