New study examines real impact of heat pump noise in homes

As we head to Net Zero homes, and gas boilers are phased out, Air Source Heat Pumps will be installed and used to heat an increasing number of our homes. They operate differently from a gas boiler and fears have been raised about possible noise pollution but the impact of this noise inside the home has never been fully tested until now. 

A new study by experts from the Acoustics Innovation Institute at the University of Salford, published in the journal Acta Acustica, has explored how residents perceive and react to noise from heat pumps. The key finding was that only just over 5% of participants found the noise highly annoying with most reporting low-to-medium annoyance. Sudden changes in heat pump operation, such as transitions from defrost cycles to full power, led to higher annoyance than steady, continuous operation. This might have important implications for cold weather, when the units defrost more often.

The study focused on impacts in the home, designed to represent worst-case scenarios, comparing daytime background noise levels and nighttime noise levels to get a full picture of the impact.

Fifty participants evaluated noise from a pump located at different distances and operating at minimum, moderate, and maximum power levels, simulating how the sound would be heard indoors through a partially open window.

Lead researcher Dr Volkan Acun of the University of Salford said: “Our findings show that the current focus on overall sound pressure level or volume does not fully capture how people experience this noise. 

“Annoyance from heat pump noise is influenced by the character of the sound, not only its sound level. Psychoacoustic qualities such as tonality and roughness are nearly as strongly associated with annoyance as the sound level.”

Researchers found that the background noise of a neighbourhood significantly changes how noise from a heat pump is perceived. Particularly during nighttime operation, annoyance can be higher as the low background noise provides less masking of the heat pump noise. In contrast, during the day, the higher background noise can help mask the heat pump noise, making it less intrusive.

The finding could give a valuable insight to policy makers in this area.

Volkan added: “Our findings support a more context-sensitive policy approach, where acceptable noise levels from heat pumps are assessed in relation to the existing background noise, rather than through a single fixed noise level threshold applied equally across all locations and time periods.”