The potential for heat pumps to be noisy is often cited as a concern when discussing large-scale home heating decarbonisation. While we know that an overwhelming majority of heat pump owners are satisfied with the noise of their individual heat pumps, we have little understanding of the cumulative noise impact of multiple heat pumps installed in a densely populated area.

To fill this knowledge gap, Apex Acoustics, commissioned by Nesta, investigated the potential adverse effects of cumulative noise from air source heat pumps in high-density residential areas.

This study focused on terraced and semi-detached housing, modelling air source heat pumps (ASHPs) operating at the maximum noise level allowed by the MCS 020 noise standard (42 dB). By adopting worst-case scenario assumptions, the study aims to understand the uppermost limits of potential noise impacts and provide insights into probable outcomes under more typical conditions. These assumptions include:

• maximum possible housing densities
• highest ASHP sound power for all units
• all units operating at full power simultaneously
• units installed on hard surfaces like concrete or paving.

These assumptions are highly improbable in real life and consequently, the modelled cumulative noise impact is likely higher than it would be in real-life settings for these housing typologies.

Even under the most unfavourable assumptions, we did not find a significant increase in noise levels from multiple heat pumps. The cumulative noise impact of multiple ASHP installations in a high-density neighbourhood would not typically be distinguishable from that of a nearby single air source heat pump installed within MCS guidelines.

• The cumulative noise level from air source heat pumps is below the threshold established for transportation (road traffic) noise, above which adverse effects are known to increase sharply.
• While cumulative noise may raise background levels in some scenarios, it remains comparable to typical urban nighttime noise.
• Noise increase from multiple ASHPs ranges from 2-8 dB, with the highest increase in gardens without fences.
• Positioning ASHPs near fences reduces noise levels by 1-3 dB compared to placing them at the centre of the rear façade.
• Even in a worst-case scenario, multiple heat pumps are unlikely to be individually distinguishable from background noise. Only the sound of the nearest heat pump may be individually distinguishable to households. However, the current MCS noise limits are designed to ensure that heat pumps cause minimal disturbance to neighbours.
• The research shows that the current planning noise limits for individual heat pumps are effective at preventing any significant noise effects from multiple installations. We therefore support the retention of the current 42db noise limit.