Sound level reference points
Whisper: ~30 dB.
Quiet bedroom at night: 35 dB.
Modern monobloc heat pump (1m away): 40–48 dB.
Refrigerator: 40–45 dB.
Quiet conversation: 50 dB.
Dishwasher: 55–65 dB.
Vacuum cleaner: 70 dB.
MCS 020 noise standard (the legal requirement)
All UK MCS-certified heat pump installations must comply with MCS 020.
Maximum 42 dB at the nearest neighbour's window (1m from window facade).
Calculated via standardised acoustic-propagation formula based on unit specification + distance + obstacles.
Failing this calculation requires moving the outdoor unit, adding sound enclosure, or selecting a quieter unit.
Acoustic statement is part of the planning application (where required) and the MCS install record.
How to spec a quiet install
Choose a slim modern unit: Vaillant aroTHERM Plus, Daikin Altherma EBLA, Mitsubishi Ecodan PUZ-WM all run at 38–43 dB.
Site away from neighbour-facing walls: rear of property is best.
Avoid corner-court or narrow back-yard locations — sound bounces.
Consider a sound enclosure (£200–£400) for tight sites.
Mount on rubber-isolation feet (standard in modern installs) to prevent vibration transfer.
Avoid mounting on a hollow wall — the wall itself can amplify low-frequency vibration.
FAQ
Will I hear the heat pump from inside my home?
Almost never. The outdoor unit is on an external wall, and walls + windows attenuate 25–40 dB of outdoor noise. Indoor sound from a typical install is below 25 dB — inaudible.
What's the chance my neighbour will complain?
Very low. The MCS 020 standard limits the unit to 42 dB at their window — quieter than typical urban background noise (45–55 dB). Properly-sited installations rarely generate complaints.
Are heat pumps noisier than gas boilers?
Slightly. A modern condensing gas boiler runs around 35–40 dB during firing; a heat pump runs 40–48 dB outside continuously. Indoors, you'll hear neither — the heat pump is outside, the boiler is inside but quieter.
What if my installer recommends a noisier unit?
Ask for the unit's dB rating at 1m and rated heat output. A 14 kW unit at 50 dB is acceptable in a large rural garden but not for a tight London terrace. The acoustic statement should pass the MCS 020 check at your specific site.
Sources
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