Worried a heat pump will be too loud? In most homes and small commercial sites, modern air source heat pumps are quieter than people expect. Typical running sound is comparable to that of everyday appliances, and there are clear UK rules on what’s acceptable at your boundary. Let’s take a closer look.
How loud is a modern heat pump
Most modern ASHPs sit somewhere around 40–60 dB(A) when running, measured a metre from the unit. That puts them in the same zone as a fridge hum or a normal conversation. It may climb a little for short periods in very cold weather or during a defrost, but this is brief.
To put those numbers in context, UK hearing charities list around 40 dB for a quiet library and around 60 dB for ordinary speech. These references help translate what you might hear in the garden or through a closed window.
What neighbours actually hear
In England, there is now a clear planning test for domestic installs. From 29 May 2025, permitted development checks use MCS 020 a), which requires the calculated level at the neighbour’s nearest opening (typically a door or window of a habitable room) to be no more than 37.0 dB(A) LAeq,5mins. In everyday terms, that is very quiet – library‑like.
At the same time, England’s planning rules were updated so that more homes can use permitted development. Key changes include allowing units within 1 metre of the boundary, increasing the maximum unit size to 1.5 m³, and allowing two units on a detached house – but you still have to pass the MCS 020 a) noise check. Scotland, Wales and Northern Ireland currently continue to reference the earlier MCS 020 version for PD.
Worried about complaints? A UK government review found that noise complaints were rare, and usually related to poor siting or installation. Separate commentary from the Institute of Acoustics highlights survey work where 57% of people noticed barking dogs, while only 4% noticed a heat pump heard indoors. That gives a sense of scale against everyday neighbourhood sounds.
Why distance and shielding matter
Sound drops off with distance. In free air, every time you double the distance from a point source, the level falls by roughly 6 dB. So if a unit measures 55 dB(A) at 1 metre, it is about 41 dB(A) at 5 metres and ~35 dB(A) at 10 metres, before any barriers. This simple rule of thumb is why moving a unit a couple of metres can turn “audible” into “barely there”.
Shielding also helps, but details matter. MCS 020 a) sets out what counts as a barrier and how much it can reduce the noise depending on whether it fully blocks the line of sight to the neighbour’s opening:
- A Type 1 barrier (solid brick or a solid fence at least 18 mm thick, with no gaps) that fully blocks the view gives a 10 dB reduction.
- A Type 2 barrier (solid but thinner fence) can give 5 dB if it blocks the view.
- Vegetation or slatted fencing doesn’t count as a barrier for the calculation.
This is why a plain, gap‑free fence panel or wall placed to break the sightline between fan and listener can be so effective.
Reflective surfaces matter too. Squeezing a unit into a corner increases the number of reflecting planes, which can lift the level in certain directions. The MCS method accounts for this using a directivity factor and even warns that very tight light‑wells will fail. In practice, giving the unit some breathing space away from two hard walls helps.
Quick comparison table
The table below combines everyday sounds with a simple worked example so the numbers feel real. Everyday values utilise well-known references; the heat pump distance figures employ the 6 dB per doubling rule of thumb and a notional 55 dB(A) at 1 metre.
| Sound or scenario | Typical level |
| Quiet library | ~40 dB(A) |
| Fridge hum | ~55 dB(A) |
| Normal conversation at 1 m | ~60 dB(A) |
| Vacuum cleaner nearby | ~70-75 dB(A) |
| Modern ASHP at 1 m | ~40–60 dB(A) |
| Same ASHP at ~5 m free field | ~41 dB(A) if 55 at 1 m |
| Same ASHP at ~10 m free field | ~35 dB(A) if 55 at 1 m |
| With a Type 1 solid screen that blocks the view | subtract up to 10 dB at the receiver (geometry dependent) |
Residential and commercial settings
(For homes in England, installers now use MCS 020 a) to show the neighbour’s assessment position will be ≤ 37.0 dB(A) LAeq,5mins, which is how most domestic projects qualify as permitted development. The method explicitly factors in distance, reflections and barriers, so good siting usually solves noise concerns without fuss.
For commercial and mixed‑use sites, planning officers typically ask for a BS 4142 assessment. In short, you compare the rated level of the plant (including any tonal or intermittent penalties) with the background level outside the nearest homes. The British Standard’s guidance is often summarised as around +5 dB, indicating likely adverse impact and around +10 dB, indicating likely significant adverse impact, subject to context. The UK environment agencies’ method note explains how to apply BS 4142 consistently in regulatory work.
Practical placement tips that work
- Put it a few metres from your own and your neighbour’s windows if space allows. That distance buys you decibels for free.
- Avoid tight corners or mounting between two hard walls where reflections build up. A little space reduces the directivity effect.
- If needed, add a solid, gap‑free screen or wall that breaks the line of sight. Don’t rely on shrubs for acoustic performance.
- Use a rigid, level slab with anti‑vibration feet and keep the fan clear of obstructions. This cuts any low‑frequency rumble and prevents rattles.
- (Ask your installer to run the MCS 020 a) calculation before finalising the spot. Small tweaks in position or screen height often make all the difference.
The bottom line
Modern heat pumps are designed to be quiet and, when sited sensibly, they blend into normal background sound. England’s up‑to‑date rules mean domestic installs must meet ≤ 37.0 dB(A) at the neighbour’s opening, which is genuinely subdued. If you are planning a commercial scheme, a straightforward BS 4142 assessment will show how to keep plant at or below the local background, with penalties applied if any tone or intermittency needs attention. Put distance and line‑of‑sight first, add a simple solid screen if you need extra headroom, and you should have no trouble keeping everyone comfortable.
If you would like tailored advice on model selection, placement and any screening, we are happy to help. Start here on our air source heat pumps page, and we can help you choose and install a quiet, compliant design for your home or business.
Want to know more? Contact Clima-Tech Services for expert advice.