Heat pumps and the like: low-frequency hum annoys a growing number of people

German Environment Agency guideline has information

Quiet, constant humming is a disturbance Click to enlarge
Quiet, constant humming is a disturbance
Source: Gary Cornhouse / Fotolia.de

Complaints about low-frequency humming noises have become more frequent in recent years – especially in residential areas. The quiet, constant hum of air source heat pumps, air-conditioning systems or district heating stations in otherwise quiet neighbourhoods is often considered disturbing, even if the noise levels comply with statutory limit values. A guide by the German Environment Agency (UBA) advises all the parties of construction projects to consider the noise emissions of such large facilities in the early planning phase of a project. Once systems which hum are in operation, there are virtually no technical means to eliminating low-frequency noise.

Urban planners and building designers, heating and air-conditioning companies, as well as builders and architects – these stakeholders can help avoid urban planning conflicts if potential noise problems are pointed out in development plans. For example, the proper selection of a building heating system could help to prevent low-frequency sounds. All apparatuses should be labeled with acoustic output levels, thus enabling a comparison of noise emissions at the retail outlet. In case of doubt, a quiet heating system should be chosen, with noise levels under 55 decibels if possible, as it will also protect the building’s residents against noise. It is advisable to install the system in a location that will disturb as few people as possible.

For systems which are already installed, the local authorities can adopt measures in individual cases where people in the surrounding area suffer intolerable adverse effects and it can be proven that the system is not in compliance with best practices, for example due to an unfavourable location of the installation. Low-frequency noises can only be reduced retroactively by technical means at great cost, including removal to another location or a complicated change of housing of the entire system. Installing soundproof windows can protect against "normal" noise, but they are largely useless when it comes to low-frequency hum. 
Statutory regulations must be further developed as a precautionary measure against low-frequency noise. What is needed is a standardised technique of forecasting noise dissemination and the establishment of an appropriate level of protection against low-frequency noise. 

People can hear sounds in the range between about 20 Hertz (Hz) and 20,000 Hz. Sounds below 20 Hz can only be heard at much louder volume than song or speech. Unlike normal sounds, however, people may feel annoyance when they hear these low-frequency sounds even though they are unable to distinguish between the different low noises. This is why we generally perceive low-frequency sounds as "humming". 

A current project by the German Environment Agency ( UBA ) on the evaluation of low-frequency sounds in residential areas (Ermittlung und Bewertung tieffrequenter Geräusche in der Umgebung von Wohnbebauung) is investigating possible technical and legal framework options and what further action must be taken. The first results of the project have been compiled in a guide. The project and guide will be introduced and discussed on 14 March 2017 in Berlin.

Umweltbundesamt Headquarters

Wörlitzer Platz 1
06844 Dessau-Roßlau

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 low-frequency noise  air heat pump