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Commercial air conditioning noise: limits, assessments and complaints

Updated 23 October 2026 · SEO Dons Editorial

How do councils judge air conditioning noise?

Mostly through BS 4142. BSI describes it as methods for rating and assessing sound of an industrial and commercial nature, using outdoor sound levels to assess the likely effect on people at homes. It adds that the standard supports current UK planning guidance, has separate assessment methods for tones and for impulsive sounds, and treats the context in which a sound is heard as a significant modifier of its impact, so the setting matters as well as the decibels. The current edition is BS 4142:2014+A1:2019.

BSI's overview gives no limits, so the numbers come from councils. National planning guidance says there is no simple relationship between noise levels and the impact on those affected. Its factors include time of day, how a new source relates to the existing sound environment, and tonal character. Some noise has a greater effect at night, which is why the quietest period when plant may run matters.

What limits do councils set?

CouncilWhat its guidance says
City of LondonNew plant at least 10 dBA below the existing background level, measured one metre from the window of the nearest noise-sensitive premises; background taken as the lowest 10-minute LA90 while the plant may run; measurements and an approved report after installation
LewishamA BS 4142 report showing the rating level 5dB below the existing background level at any time
Brighton and HoveExternal plant, including air conditioning units, assessed by an acoustics specialist in line with BS 4142; no margin stated on the page

The margins differ, and national guidance explains why: plans may include noise standards, but care should be taken to avoid applying them as rigid thresholds. A design that passes in one borough can fail in another, so the local wording decides. The planning permission guide covers when an application is needed at all.

What do the national planning thresholds mean?

National planning guidance frames noise decisions around effect levels rather than one number. At the lowest observed adverse effect level, adverse effects on health and quality of life can first be detected; the noise starts to have an adverse effect and consideration needs to be given to mitigating and minimising it. The significant observed adverse effect level is where significant adverse effects occur, and if exposure is predicted to be above it, the planning process should be used to avoid the effect. Neither level is a fixed decibel figure: the guidance says effects can depend on a combination of exposure, number of occurrences, duration and time of day.

How does a BS 4142 assessment work in practice?

  1. Establish the background sound at the nearest noise-sensitive property for the hours the plant will run. The City of London uses the lowest 10-minute reading in that period.
  2. Take the unit's sound data from the manufacturer and predict its level at that property. CIBSE Guide B4 lists interpreting manufacturers' noise data among its topics.
  3. Check for tones or impulsive character, which the standard treats separately.
  4. Compare the result with the council's margin, and design mitigation if it fails.
  5. Measure again after installation where the condition requires it.

Doing this before the unit is chosen matters because the result can change where the plant goes and which model is specified. Readers planning a commercial air conditioning installation can send an enquiry through the site's form.

Which controls reduce the noise?

Planning guidance groups mitigation into engineering, layout and operating conditions, plus protection at the receiving building. Applied to air conditioning plant:

  • Unit selection (engineering). Guidance describes engineering as reducing the noise generated at source and containing it. Comparing manufacturers' sound data and fitting an acoustic enclosure or attenuated louvre both fit that description.
  • Siting and screening (layout). Guidance refers to optimising the distance between the source and noise-sensitive receptors, and to screening by purpose-built barriers or other buildings. Moving a condenser to a roof well or a screened courtyard is one example. Screening also has to leave the unit enough airflow, which is a design check.
  • Night operation (conditions). Guidance lists conditions that restrict activity at certain times or specify permissible noise levels for evenings and late at night. For plant this can mean a reduced-capacity night mode.
  • Vibration and upkeep. CIBSE's guide covers vibration isolators, and Eden District Council warns that units that are not properly maintained can rattle and hum, making more noise and vibration than normal. Anti-vibration mounts and a maintenance routine address that.

What happens if someone complains?

Noise from premises can be a statutory nuisance under section 79 of the Environmental Protection Act 1990. GOV.UK guidance for England says the issue must unreasonably and substantially interfere with the use or enjoyment of a home or other premises, or injure health. Where a council is satisfied a statutory nuisance exists, it must serve an abatement notice. For noise from premises, service can be delayed by up to 7 days while the council tries to get the noise stopped or restricted. A notice can be appealed to a magistrates court within 21 days.

For noise from business premises there is a defence of best practicable means. Eden District Council notes that planning conditions should prevent a noise nuisance, and the complaint routes sit alongside that. A person aggrieved can also bring a complaint to a magistrates court under section 82. For disputes between neighbours at homes, the GOV.UK guidance sets out the same route.

Do heat pump noise rules apply?

Not to commercial cooling plant. MCS 020 a), the sound calculation for air source heat pumps, belongs to the permitted development route for homes, as MCS explains. Hissing, rattling and buzzing inside a unit is a fault question, covered in the noisy air conditioning guide.

Sources

Common questions

Not one national figure. Planning guidance allows plans to include noise standards but warns against applying them as rigid thresholds, so councils set their own. The City of London asks for new plant to be at least 10 dBA below background, and Lewisham asks for a rating level 5dB below background.

Does a single small unit need an acoustic report?

It depends on the council. Brighton and Hove says external plant may need an acoustic assessment by a specialist in line with BS 4142, and Lewisham asks for a noise and vibration impact assessment where noise is generated. The planning officer can say what is expected for the site.

Does night-time matter more than daytime?

Often, yes. Planning guidance says some noise has a greater adverse effect at night than during the day, and the City of London sets background from the lowest 10-minute reading while the plant is or may be in operation.

Can a neighbour act without involving the council?

Yes. Section 82 of the Environmental Protection Act 1990 lets a magistrates court act on a complaint made by any person aggrieved by the existence of a statutory nuisance. Councils separately investigate and can serve abatement notices.

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