Will your heat pump meet the 37 dB(A) limit at your neighbours’ windows? Uses the official MCS 020 a) method. iFollows MCS 020 a) Issue 1.1, the calculation required for permitted development in England since 29 May 2025. It’s a planning aid: your installer must still complete the official calculation. Scotland, Wales and Northern Ireland use the older MCS 020, which isn’t covered here.
MCS 020 a) sound calculation · · heatpumpdatabase.com/heat-pump-noise-calculator/
Heat pump
Heat pump 2
Neighbours’ windows iCheck every neighbouring window or door to a habitable room (bedroom, living, dining, study) on every side and floor. Bathrooms, halls, landings and utility rooms don’t count. The nearest window isn’t always the loudest.
How the calculation works
Lp = LW + 10·log10( Q ÷ 4πr² ) − AB
Barrier
No view
Partial
Full view
Masonry wall / solid fence ≥18 mm
10 dB
5 dB
0
Solid fence <18 mm
5 dB
2.5 dB
0
Open or gappy fence, hedge
0
0
0
Two heat pumps add logarithmically (two equal units are +3 dB). Round to 0.1 dB; every window must be 37.0 dB(A) or lower. Example from MCS 020 a): 60 dB(A), Q4, 8.0 m, brick wall with partial view → 32.0 dB(A).
Where this applies
England, permitted development, since 29 May 2025 – whether or not the installer is MCS certified.
Other conditions still apply (size up to 1.5 m³, max two units on a detached house, listed buildings and Article 4 areas excluded). See the planning guide.
Scotland, Wales and Northern Ireland follow the earlier MCS 020.
Source: MCS 020 a) Issue 1.1 (14 April 2025). Sound power figures are manufacturers’ published data – confirm against the current product fiche.