Heat pump mythbusters commentary - part 5: Will my heat pump be a noise nuisance to my neighbours?

Article summary:

1. Air Source Heat Pumps typically require an external unit to draw heat from the surrounding air using fans and compressors, both of which make some noise.
2. The noise levels emitted by modern, quieter heat pumps are of a similar magnitude to other household appliances, such as fridges, dishwashers and boilers. Older heat pumps did tend to be louder.
3. There are two noise-related requirements for heat pump installations. One, from the Microgeneration Certification Scheme (MCS), is for heat pumps to produce no more than 42 decibels sound pressure, measured at a distance of 1m from an opening into a neighbouring property. The other requirement is a blanket limit on heat pumps being located within 1m of a neighbouring property to be installed without requiring planning permission. The previous government was reviewing whether to remove this planning rule.
4. People surveyed were much more likely to notice other source of noise, such as dogs (which are not subject to any noise exposure limits) than heat pumps.
5. Even in high density housing, with heat pumps operating simultaneously at their maximum capacity, the noise impact is likely to be no greater than the noise from the single closest heat pump (which itself is likely to be negligible). 

1. Whilst it is true that noise is a consideration and acoustic comfort is an important aspect of health and wellbeing, heat pumps are targeted in a way that is not applied to other sources of noise, particularly in urban environments. For example, dogs barking, cars revving, bins being collected and boiler flues gurgling away are all aspects of life we have come to accept, and which are not subject to the same scrutiny as heat pumps. Not to mention the fact it’s perfectly legal to set off fireworks on private land between the hours of 7am – 11pm, all year round.

2. The science of sound and perception of noise are not that intuitive – so much so that we are planning a more in-depth article on this topic! As a very high-level summary, noise generated by a source is measured as sound power but perceived by people as sound pressure, which decays with distance from the source. The unit of both sound power and sound pressure is the decibel (dB) and decibels add logarithmically rather than arithmetically. As a result, a source of noise which is 10 dB lower than another source of noise is barely noticeable. In addition, human perception of sound is different at different frequencies, with low and high frequencies being less noticeable than mid-range frequencies. Furthermore, the quality and type of sound and the context in which it is heard have a big impact on whether it is perceived negatively. To summarise – a single headline figure for sound cannot tell the whole story.