If you’re planning to install an air source heat pump or a commercial air conditioning unit, there’s a good chance your local council will require a Noise Impact Assessment before granting planning permission. In most cases, this is carried out using the British Standard BS 4142:2014+A1:2019—but what does that mean, and do you actually need one?

This article explains when a BS 4142 noise assessment is needed, what it involves, and how to make sure your installation meets planning requirements.

Why Is a Noise Assessment Required?

Heat pumps and other external plant equipment generate low-frequency and sometimes tonal noise. While these systems are far quieter than traditional boilers, their constant or cyclical operation—especially at night—can disturb nearby neighbours if not properly sited or enclosed.

Local planning authorities have a duty to protect residential amenity, and that includes ensuring new installations don’t create noise nuisance.

When Do Councils Request a BS 4142 Assessment?

You’ll usually need a noise assessment if:

• The unit is within 1–2 metres of a neighbouring property or boundary

• The installation is in a quiet, rural, or suburban area

• Your property is part of a new development or extension being submitted for planning

• You’re fitting multiple heat pumps or commercial AC units

• The unit is near a bedroom window or private garden space

Even permitted development installations may trigger complaints if noise isn’t considered properly. In those cases, retrospective assessments are often required.

What Is BS 4142?

BS 4142:2014+A1:2019 is the UK’s standard method for assessing the impact of industrial and commercial noise on people nearby. It compares the noise level of the equipment (known as the rating level) to the existing background sound level at the site.

Key factors assessed include:

• Tonal or impulsive characteristics (e.g. humming or droning)

• Time of day (night-time operation is more sensitive)

• Distance to sensitive receptors (e.g. homes)

• Existing background noise levels

If the rating level is significantly above the background level, the equipment may be considered to cause an adverse impact, requiring noise reduction measures.

What Happens in a Noise Survey?

A professional noise consultant will:

1. Visit your site to measure baseline (background) noise levels

2. Assess the sound data for the heat pump or AC unit—usually provided by the manufacturer

3. Predict the impact of the installation using BS 4142 methods

4. Recommend mitigation (if needed), such as acoustic fencing, enclosures, or relocation

5. Produce a clear, planning-ready report for submission

Common Mitigation Measures

If the assessment shows a potential noise issue, your consultant might suggest:

• Acoustic barriers or fencing around the unit

• Relocating the unit further from sensitive areas

• Low-noise models or inverter-controlled equipment

• Reducing night-time operation or programming quieter cycles

These solutions often allow you to keep the equipment you want while staying within acceptable limits.