Modern air source heat pumps are significantly quieter than older generations. Most domestic units run at around 40-45 decibels measured at close range — roughly the level of a quiet conversation, or a fridge humming in a kitchen.
What affects real-world noise isn't just the unit's rated figure. It's:
- Where the outdoor unit is sited — we avoid placing it directly under bedroom windows or against reflective walls that can amplify sound
- How it's mounted — vibration absorbers and a solid level base stop low-frequency drone from travelling through the wall
- Distance from the nearest neighbour's habitable room window — the MCS planning standard (MCS 020) requires a formal noise calculation before sign-off, and we complete this on every install
- Defrost cycle — in cold damp weather the unit briefly defrosts its coil, which is slightly louder for a short time
Under the MCS planning standard the predicted noise has to stay at or below 42 decibels at the assessment position — measured one metre outside the centre of a door or window of a habitable room in a neighbouring property. Habitable room is a specific term here: bathrooms, shower rooms, toilets, and kitchens don't count, so a unit sited near a neighbour's kitchen window is assessed differently from one near their living room.
This matters in Scotland because Class 6H of the Scottish permitted development rules makes compliance with the MCS planning standard a condition of installing without planning permission. Come in above 42 dB and the job needs a full planning application instead. We design every install to meet the limit and document it as part of the paperwork under JME Green Energy's MCS certification.