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Air source heat pumps (ASHPs) are becoming an increasingly popular method for providing hot water and heating in homes, offering an alternative to gas boilers, which are currently installed in around 80% of homes in England and Wales.
What are heat pumps?
ASHPs are electrically powered units, often with components located both inside and outside the building they serve. They work by extracting heat from the outside air, a virtually limitless renewable resource, and transferring it into the home. Some key benefits of ASHPs include higher energy efficiency compared to gas boilers and their use of a renewable energy source when combined with photovoltaic panels, which aligns with environmental sustainability goals.
Given the UK government’s plans to ban the installation of gas boilers in new-build homes from 2035 onwards, the rising interest in ASHPs is unsurprising. Additionally, the Boiler Upgrade Scheme (BUS), currently offered by the government, provides financial incentives for homeowners to switch to more sustainable heating solutions, further encouraging the transition away from non-renewable energy sources.
Potential noise issues
A potential drawback of switching from internal boilers to external ASHPs is the introduction of a different type of noise to the environment, which could affect neighbouring properties. While boilers and their external components (the exhaust flue) are not silent, the external placement of ASHPs and the type of noise they make may make their sound more perceptible to neighbouring properties. The primary sources of noise in ASHPs include the external fan, which is used to draw in air and pass it over a heat exchanger, and the compressor, which increases the pressure (and temperature) of the evaporated liquid refrigerant. Secondary sources, such as valves and heat exchangers, also contribute to the overall noise level, though to a lesser extent.
ASHPs can be installed under Permitted Development Rights (PDRs) in most residential areas, meaning a planning application is not typically required, provided the installation complies with the Microgeneration Certification Scheme (MCS). The MCS includes guidelines aimed at minimising noise impacts on nearby properties. Specifically, the MCS requires that the combined noise level of the ASHP and an assumed background noise level of 40 dB(A) must be less than or equal to 42 dB(A) at the nearest noise-sensitive receptor (typically a neighbouring property). This translates to a maximum permissible ASHP noise level of 37 dB(A) at the receptor.
This assessment is based on the British Standard BS 4142 for noise impact, but it’s simplified to avoid the need for a detailed noise survey. It also simplifies how corrections are made for factors like distance and screening, which means the assessment can be done more quickly, even by non-acousticians.
However, the MCS assessment has some limitations. For example, in areas where background noise levels are higher than 42 dB(A), it may unnecessarily restrict the installation of larger ASHPs, even though the noise they make would likely be ‘masked’ by the existing background noise. Additionally, the MCS does not account for variations in background noise between daytime and nigh time, which could lead to incorrect noise limits during certain periods.
While ASHPs might introduce some additional noise in certain areas, selecting the right unit and carefully considering its location can minimise potential impacts in most cases.
For further information on the MCS or if you need a detailed noise survey and assessment, please feel free to reach out to one of our Noise and Vibration experts.