UK Heat Pump Finder
How loud is a heat pump, really?
Modern air source heat pumps typically produce around 40-60 dB at close range. For context, that's roughly in the territory of a quiet conversation or a domestic fridge. Most owners report noticing it for the first few weeks and then largely tuning it out.
The sound comes from two places: the compressor and the fan. You'll hear it more when the unit is working hardest — very cold days, and during defrost cycles.
Sizing matters more than the badge on the unit
A heat pump that's the wrong size for the home is noisier in practice than one that's correctly sized, regardless of the manufacturer's quoted figures:
- Undersized — runs flat out for long periods in cold weather, at its loudest setting.
- Oversized — cycles on and off repeatedly, and the starts and stops are the most noticeable part of the sound.
A correctly sized unit running steadily at a low flow temperature is the quietest outcome — which is why the room-by-room heat loss calculation matters for noise, not just for efficiency and radiator sizing.
Do you need planning permission?
For most homes, no. Air source heat pumps generally fall under permitted development, meaning no planning application is needed provided conditions are met. England's rules were significantly relaxed in 2025:
- The old 1-metre boundary restriction was removed — this was the single biggest obstacle for terraced houses, semis and smaller plots
- The outdoor unit size limit for houses increased from 0.6m³ to 1.5m³
- Up to two units permitted at a detached house
- Systems that provide cooling as well as heating are now included (provided they're not used solely for cooling)
You will still need permission if…
- The property is listed — Listed Building Consent is always required, permitted development never applies
- It's a flat above ground floor, in most cases
- You're in a conservation area with an Article 4 direction
- The installation fails the noise condition at every viable position
The noise condition — and an honest caveat
Permitted development depends on passing a calculation under MCS 020, the planning standard that estimates your unit's sound level at a neighbour's habitable room window. Your MCS-certified installer carries out this calculation — it's their responsibility, not yours.
Rules differ across the UK
| Nation | Position |
|---|---|
| England | Most permissive — 1-metre boundary rule removed (2025), 1.5m³ size cap on houses, up to two units on detached homes |
| Wales | Stricter — reported 3-metre boundary clearance, 1m³ size cap, one unit per property |
| Scotland & Northern Ireland | Broadly similar to England's pre-2025 rules, including a 1-metre boundary requirement |
Devolved planning rules change independently of England's. Always confirm current requirements for your nation before proceeding.
If the calculation doesn't pass
A failing result usually isn't the end of the project. Common fixes:
- Relocate the unit — further from neighbouring windows, or where a fence or wall breaks the line of sight
- Add an acoustic barrier or enclosure — provided it doesn't restrict airflow, which your installer will advise on
- Choose a quieter model — current-generation R290 and R32 units are meaningfully quieter than those from a few years back
- Apply for planning permission — adds cost and time, but is a legitimate route if no siting passes
The noise calculation and siting survey are part of what an MCS-certified installer does as standard.
Find MCS-certified installers near you →