MCS 020 heat pump noise rules in UK 2026: the homeowner's guide

Why MCS 020 matters more than the headline number

The 42 dB(A) figure isn’t about whether you can hear the heat pump — modern heat pumps in normal operation are quieter than a fridge. The figure is the threshold that determines whether your install qualifies as permitted development.

Permitted development = no planning application, no £200-£500 fee, no 8-12 week wait, no risk of refusal. Fall outside PD and you face a full application, which can be refused on noise, visual amenity, or neighbour objection grounds.

So MCS 020 is a planning gate, not a comfort threshold. Worth understanding because most installs CAN pass it with thoughtful siting — and a small minority of homes genuinely cannot, in which case the conversation moves to planning permission early in the process.

The full permitted development criteria — MCS 020 is one of five

Class G of the Town and Country Planning Order grants PD rights for ASHPs subject to FIVE conditions, all of which must be met:

• MCS 020 noise calcshowing ≤42 dB(A) at the nearest neighbour’s habitable-room window.
• Single unit only — one ASHP per dwelling under PD.
• Volume ≤1 m³for the outdoor unit (the indoor unit doesn’t count).
• Not on a wall or roof facing a highway (for properties in conservation areas / Article 4 zones).
• Listed buildings excluded from PD — always need planning consent.

MCS 020 is the noise gate; the other four are siting constraints. All five must pass for PD.

How the MCS 020 calculation actually works

The calculation uses three primary inputs:

1. Sound Power Level (SWL)

The heat pump’s declared dB(A) output, measured per ISO 9614-2. Manufacturers publish this on the technical datasheet. Typical UK 2026 figures:

• Quiet R290 units: 50–54 dB(A)
• Standard R32 units: 55–60 dB(A)
• Older / larger units: 60–68 dB(A)

2. Direct distance to nearest habitable window

Straight-line distance from the proposed outdoor unit location to the nearest neighbour’s habitable-room window — bedroom, living room, kitchen-diner. Bathrooms, hallways, and stairwells don’t count.

Sound pressure level halves (drops by ~6 dB) for every doubling of distance. So:

• 1m: full SWL minus minor distance correction.
• 2m: SWL − 6 dB.
• 4m: SWL − 12 dB.
• 8m: SWL − 18 dB.

3. Reflection and barrier corrections

Walls behind the unit reflect sound forward, adding +3 dB. Walls or fences in the line of sight to the receiver block direct sound, subtracting up to 10 dB depending on height and material. The MCS 020 tool applies these automatically once the installer enters the geometry.

Worked example — a typical UK semi

Scenario: 3-bed semi, heat pump on the side wall, 5m line-of-sight to the neighbour kitchen window. No fence in between.

• SWL: 56 dB(A) (mid-range R32).
• Distance correction at 5m: −14 dB.
• Reflection from rear wall: +3 dB.
• No barrier: 0 dB.
• Calculated SPL at window: 56 − 14 + 3 = 45 dB(A). Fails MCS 020 by 3 dB.

Two fixes available:

• Add an acoustic fence in the line of sight, ~1.8m high, between the unit and the neighbour boundary. Drops apparent noise by 5-8 dB. New result: 45 − 6 = 39 dB(A). Passes.
• Move the unit to the rear of the property, increasing distance to 8m, away from the kitchen window. 56 − 18 + 3 = 41 dB(A). Passes.

Properties most at risk of failing

• Terraced houses with narrow side passages. Outdoor unit usually has to go in the back garden near the neighbouring fence — short distances to two adjacent properties’ rear windows.
• End-of-terrace with the “outside” wall facing a neighbour. Often a 1-2m alley between houses; insufficient distance.
• Maisonettes and small flats where the only outdoor space is balcony or shared back court.
• Older Victorian terraces in conservation areas with the added Article 4 visual constraint on top of MCS 020.

What to do at the site visit stage

During the MCS site visit your installer should:

1. Identify the nearest habitable window on the closest neighbouring property.
2. Measure the proposed unit location distance to that window.
3. Note any reflective surfaces or barriers.
4. Run the MCS 020 spreadsheet calculation (either on site or in the quote follow-up).
5. Document the calculation in your quote with the SWL of the proposed unit, the geometry, and the result.

Ask to see the calculation. If the installer can’t produce it on request, that’s a flag — every MCS-certified install needs it for the MCS Installation Certificate.

If you genuinely cannot pass MCS 020

A small minority of UK homes (perhaps 5-10% of urban terraces) genuinely cannot site an air-source heat pump within MCS 020 limits. Options:

• Apply for planning permission with a full noise impact statement. £200-£500 fee, 8-12 weeks, refusal possible.
• Consider ground-source heat pump which has no external noise but needs ~80m² of garden for slinky loops, or ~30m depth for a borehole. See the ASHP vs GSHP comparison.
• Consider a hybrid systemwith a smaller heat pump for off-peak heating + retained gas boiler for cold-snap peaks. The smaller unit may satisfy MCS 020 where a full-size one wouldn’t.
• Wait for newer quieter models. R290 and 2026-generation R32 units are 4-8 dB quieter than the 2020 generation. The bar may move.

The summary

MCS 020 is a planning calculation, not a comfort threshold — modern heat pumps are very quiet in operation. The 42 dB(A) limit at the nearest neighbour habitable window is the gate that separates permitted-development installs from planning-permission installs. Most UK semis and detached homes pass with sensible siting; terraces are tight; some genuinely fail. Ask your installer for the MCS 020 workings on any quote and confirm the result before signing — it determines whether your install timeline is 4-10 weeks or 12-22 weeks.