What is the legal noise limit for heat pumps under UK Permitted Development?

Under English and Welsh Permitted Development (Class G), domestic air source heat pumps must not exceed 42.0 dBA at the nearest assessment position (typically your neighbour's closest habitable room window or glazed door).

How is the MCS 020 acoustic sound calculation performed?

The MCS 020 formula starts with the manufacturer tested sound power level (LwA). It applies hemispherical distance attenuation: -20 * log10(distance) - 8. Then it adds acoustic reflection factors: +3 dBA if mounted against a flat brick wall, or +6 dBA if sited in an enclosed internal corner with two reflecting surfaces.

What is the minimum distance a heat pump can be from a property boundary in England?

The outdoor unit must be installed at least 1.0 metre away from any boundary of the curtilage of the dwellinghouse to satisfy standard Class G Permitted Development regulations.

What if my heat pump exceeds 42 dBA at the boundary?

If your installation exceeds 42.0 dBA at the assessment point, it does not qualify for Permitted Development and you must apply for full formal planning permission from your local municipal planning authority.

Planning Permission Diagnostic

Heat Pump Noise & MCS 020 Planning Calculator

Under UK Permitted Development rules, domestic heat pumps must not exceed 42.0 dBA at your nearest neighbour's assessment window. Use our official acoustic formula to verify compliance in seconds.

Interactive Acoustic Engine

MCS 020 Boundary Sound Calculation

Select your preferred heat pump model and adjust the distance to your neighbour's closest window.

1. Select Heat Pump Model

2. Distance to Nearest Neighbour's Window: 3.0 metres

1.0m (Tight Terrace) 3.0m (Standard Semi) 15.0m (Large Detached)

3. Wall Mounting Siting

4. Boundary Barrier

✅ 100% Permitted Development Compliant Statutory MCS 020 Standard

Calculated Sound at Window

32.8 dBA

Legal UK Planning Limit

42.0 dBA

Calculated sound level is well below the statutory limit.

No planning permission required for standard domestic installation.

Official Documentation

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Need statutory evidence for council planning officers, neighbours, or mortgage surveys? Claim your free signed MCS 020 compliance summary and match with accredited local engineers to verify on-site acoustics.

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How England & Wales MCS 020 Noise Rules Work

In England and Wales, installing an air source heat pump is considered Permitted Development under the Town and Country Planning (General Permitted Development) Order, meaning you do not need to submit a formal council planning application, provided:

The 42.0 dBA Rule: The sound pressure level from the heat pump must not exceed 42.0 dBA at the nearest assessment point (typically your neighbour's ground floor or first-floor bedroom window).
Volume Restriction: The outdoor compressor unit must not exceed 0.6 cubic metres in external volume.
Boundary Clearances: In England, the outdoor unit must sit at least 1.0 metre from your property boundary (or comply with MCS 020 calculations).
Conservation Areas: Permitted development still applies in many conservation zones unless specific Article 4 Directions or listed building restrictions apply.

Decibel Comparison Chart (Real-World Reference)

Sound Source	Sound Pressure (dBA)	Comparison to Modern Heat Pumps
Whisper in a quiet library	20 – 25 dBA	Equivalent to Mitsubishi Ecodan / Vaillant in night-silent mode at 3m.
Modern domestic refrigerator hum	30 – 35 dBA	Identical to a modern heat pump running at normal daytime load at 3 metres.
Statutory MCS 020 Permitted Development Limit	42.0 dBA	The legal ceiling allowed at your neighbour's window.
Moderate rainfall / quiet conversation	50 – 55 dBA	Significantly louder than an MCS-compliant heat pump installation.
Traditional gas boiler flue blast	55 – 60 dBA	Traditional gas boilers blast flumes intermittently with noticeable noise.