Heat pump sound assessments: why early planning matters for housebuilders & developers

According to findings from research and innovation foundation Nesta, between 2015 and 2026, more than 11,000 residential heat pump planning applications were rejected, with noise cited in 43% of cases. At scale, those delays can significantly impede progress. For developers, the focus is not whether an ASHP needs a sound assessment, but how to design sites in the first place so that sound assessments don’t become an issue.

The shift to MCS 020 a): what developers need to know

The updated MCS 020 a) is now fully in force in England and Wales. This sets a maximum predicted noise level of 37 decibels (dB) at every assessment position. While this is lower than the previous 42 dB limit, it’s important to note that the new figure is not simply viewed as ‘5 dB less than the old limit’, as the new standard introduced a revised calculation method, including different treatment of assessment positions, reflecting surfaces and barriers. The two figures therefore belong to different versions of the assessment.

The revised standard also introduced new measures around boundaries. Previously, ASHP units in England needed to be installed at least one metre from the property boundary, and at least three metres in Wales. Both rules have since been removed.

The move from fixed boundary distances towards a noise-based assessment gives housebuilders more freedom, particularly where space is limited. However, it also places greater responsibility on developers to assess the sound impacts of each site properly.

For developers, this shift is significant. Instead of relying on simple boundary rules, compliance now depends on how each ASHP interacts acoustically with the built environment. That means noise needs to be considered early in the planning stage, not left to installers to solve plot by plot.

Do housing developments need planning permission for ASHPs?

The majority of compliant domestic installations benefit from Permitted Development Rights (PDR) and therefore do not require formal planning approval as long as:

• The unit meets MCS 020 a) noise limits

• The system is correctly positioned

• Only one outdoor unit is installed

• The property is not restricted by special planning conditions (for example, it’s a listed building or located in a conservation area)

However, housing developments in their totality are not automatically granted PDR, and require master planning permission. The overall development planning application should include proposed plans for ASHPs – a separate application is not required.

The ASHP component of new build development planning permission does not typically present challenges if it aligns with the criteria above. However, overall planning consent lies with the local council, which may demand a full BS4142 sound assessment if deemed necessary. This is why it’s critical to consider ASHPs in development plans from the start.

Why early design decisions matter

On higher density developments, the acoustic environment is shaped long before a heat pump is specified. Key factors include:

• Plot orientation: Where do neighbouring habitable rooms face?

• Spacing between units: Tighter plots reduce natural attenuation.

• Facade design: Reflective surfaces can amplify noise.

• Shared outdoor spaces: Courtyards, car parks and mews layouts can create echo pathways.

• Apartment blocks: External ASHP locations become critical, especially near bedrooms.

Many of these factors are fixed by the time ASHPs are being installed, so developers who integrate noise considerations early on can avoid costly redesigns, planning delays or the need for full BS4142 assessments later.

Designing out noise: what housebuilders should prioritise

Noise mitigation is far easier when it’s incorporated into the design stage, instead of being tackled retrospectively. Developers can reduce risk by focusing on five core principles:

1.  Add distance

   Increasing distance between ASHPs and neighbouring windows is the most effective mitigation. Even small adjustments in plot layout can significantly reduce predicted noise levels.

2. Consider air discharge

   ASHP units discharge air from the front of the unit – this is where the sound levels are highest. Avoid facing this towards habitable rooms, especially bedrooms and living areas, on adjacent plots or blocks.

3. Use barriers

   Acoustic barriers such as walls, fences and vegetation can reduce sound. A concrete or masonry barrier between the unit and a neighbour’s habitable room can provide up to 10 dB attenuation. But don’t allow barriers to restrict airflow to the unit, and don’t enclose the unit on three or more sides.

4. Avoid acoustic traps

   Courtyards, narrow passages and enclosed spaces can amplify noise. Early modelling can help identify and redesign these risk areas.

5. Select appropriate units

   Manufacturers now offer low noise models designed for constrained or noise sensitive sites. Developers should specify these strategically, rather than leaving selection to installers. Additionally, measures such as anti-vibration mounting and pads can help mitigate noise further.

Looking ahead

Policy bodies are working to streamline heat pump planning. For example, Nesta’s has called for the extension of permitted development rights to Grade II listed buildings, while the Institute of Acoustics has published new guidance aimed at reducing assessment costs. But these changes also shift responsibility upstream, putting the onus on developers to demonstrate that noise has been properly considered across the whole site.

Heat pump noise is no longer an installer level detail. It’s a site design variable, a planning risk, and a customer satisfaction issue. By integrating acoustic thinking into planning early, developers can reduce planning delays, avoid costly BS4142 assessments, improve customer comfort and help to future proof developments as heat pump uptake accelerates.

Planning an upcoming development? Our heating specialists can help you consider noise, product selection and system design from the outset.

Contact us to discuss your project.