How Loud Is a Heat Pump? The UK Noise Rules

In England a domestic heat pump is permitted development only if the calculated sound pressure level is 37.0 dB(A) or lower at every assessment position, and MCS 020 a) puts those positions 1m outside a neighbour's habitable room window. The calculation starts from the unit's sound power level, then takes off distance and any solid barrier in the way.

Where the 37.0 dB(A) limit comes from

Paragraph 1.2 of MCS 020 a) Issue 1.1, dated 14/04/2025, states that the standard includes a calculation procedure designed to confirm whether the permitted development noise limit of 37 dB LAeq,5mins would be met at the assessment positions, ignoring the effect of the façade. Step 8 of its own calculation table asks whether the result is equal to or lower than the permitted development noise limit of 37.0 dB(A).

That standard became the one England's planning rules point at on 29 May 2025. Article 6 of the Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025 amended the definition of "MCS Planning Standards" in paragraph P of Part 14 of the 2015 Order, substituting "MCS 020 a) - Air Source Heat Pump Sound Calculation (For Permitted Development Installations)" for the previous reference to MCS 007. Its footnote names Issue 1.1 dated 14th April 2025 and gives the mcscertified.com address the document sits at.

Check which document a decibel figure came from before you rely on it, because the standard was split as well as revised. The foreword to MCS 020 a) explains that the previous MCS 020 standard combined air source heat pumps and wind turbines into one standard, and that these have now been separated into two new standards: MCS 020 a) for air source heat pumps and MCS 020 b) for wind turbines.

Compliance with the sound calculation is not the whole of the test. Paragraph 1.3 of MCS 020 a) says that compliance with the standard on its own does not bestow permitted development rights, that there are a number of other conditions and limitations which must be complied with, and that the full requirements for installations in England can be found in the Town and Country Planning (General Permitted Development) (England) Order 2015.

What the 37.0 dB(A) is measured at

MCS 020 a) defines the assessment position as a position 1m external to the centre point of any door or window to a habitable room of a neighbouring property, measured perpendicular to the plane of the door or window. So the test is taken at your neighbour's window, not at your boundary and not at your own back door.

• Habitable room covers, in the standard's words, "any rooms used or intended to be used for sleeping or living which are not solely used for cooking purposes", and it does not include bath or toilet facilities, service rooms, corridors, laundry rooms, hallways or utility rooms.
• Neighbouring property means any building used for any of the purposes of Class C of the Use Classes Order 1987 as amended, which the standard says includes dwellings, houses, hotels, residential institutions and houses in multiple occupation. Where the heat pump would go on a block of flats, it includes other flats in the same block.
• Every affected position counts. Paragraph 1.6 requires contractors to complete one table for each assessment position that could potentially be affected by noise from the heat pump, so a ground floor window and a first floor bedroom are separate sums.

The standard also sets out what the installer leaves behind. Paragraph 1.7 says installers shall insert their results in the result column for each step, and that contractors shall retain one copy of the completed table for their records and provide another copy to the customer. Ask for that copy, because the standard says one is yours.

The brochure decibel is usually the wrong number

Step 3 of MCS 020 a) says the A-weighted sound power level should be obtained from manufacturer's data, found on the product fiche, product energy label or the MCS product database, and that it is important to use the sound power level and not the sound pressure level as these are two different quantities. It adds that if a datasheet uses a generic term such as "noise level" and it is not explicitly clear which quantity is meant, clarity should be sought from the manufacturer before starting the assessment.

The gap between the two quantities is wide enough to catch you out. Midea states that its M Thermal R290 produces a 44dB ErP sound pressure level at 1 metre, which is a quieter-sounding figure than the sound power level the planning sum needs. We go through that range in our guide to Midea heat pumps in the UK.

Viessmann and Ideal both publish the sound power figure the sum needs.

• Viessmann publishes the Vitocal 200-A ie at 48 dB(A) for unit size 06, 53 dB(A) for size 08, 54 dB(A) for size 10 and 55 dB(A) for size 12, at rated heat output under ErP.
• Viessmann publishes maximum sound power at rated heat output for the same unit of 56 dB(A) for size 06, 59 dB(A) for size 08 and 61 dB(A) for sizes 10 and 12.
• Ideal publishes the Logic Air, measured to EN 12102-1, at 52 dB(A) for the 4kW and 5kW units and 55 dB(A) for the 8kW and 10kW units.

One figure you cannot use is the quiet one. Step 3 of MCS 020 a) states that the sound power level in low noise mode shall not be used. Viessmann publishes sound power in quiet operation Level 2 for the Vitocal 200-A ie of 54 dB(A) for unit size 06 and 56 dB(A) for sizes 08, 10 and 12, and those are not the numbers the assessment takes. The model-level detail for both brands is in our guides to Viessmann heat pumps and Ideal's Logic Air.

Distance and walls do most of the work

Step 7 of MCS 020 a) gives the sound pressure level at the assessment position as Lp = Lw + 10.log(Q / 4.π.r²) − A_B, where Lw is the sound power level in dB(A), Q is the directivity factor, r is the distance from the heat pump to the assessment position in metres and A_B is the barrier attenuation in dB(A).

Reflective surfaces push the result up. Step 4 says the sound pressure level increases with the number of reflecting surfaces, that a reflective surface is any surface including the ground but not vegetation within 1 m of the heat pump, and that the surface must extend beyond the edge of the heat pump by 1m or more in two or more directions. The standard's own examples are Q2 for one reflecting surface, Q4 for two, and Q8 for three. A heat pump with more than three reflective surfaces, the standard says, for example those within small lightwells, will not meet MCS 020 a).

A solid barrier pulls it back down, and a hedge does nothing. The standard defines a Type 1 barrier as a solid brick or masonry wall, or a solid fence at least 18mm thick, with no cracks or gaps and extending horizontally by 1m or more from either edge of the heat pump. A Type 2 barrier is a solid fence less than 18mm thick on the same terms. Its matrix gives 10 dB of attenuation for a Type 1 barrier with no view of the assessment position, 5 dB with a partial view and 0 dB with a full view, and 5 dB, 2.5 dB and 0 dB respectively for Type 2. Open fences, fences with gaps and cracks, vegetation, and walls or fences in a poor state of repair are listed under "no barrier" and score 0 dB.

MCS's own worked example, in a real garden

Appendix A of MCS 020 a) works a 60 dB(A) unit at a detached house in Chester through three assessment positions, and all three clear the limit. Those three sums are worth reading before you argue with anyone about where the box goes, because they show how much slack the calculation has in it.

• Assessment position 1 is a first floor left rear bedroom window at 16 Willis Close, Chester, 8.0 m from the unit behind a brick wall with partial line of sight, and the calculated sound pressure level is 32.0 dB(A).
• Assessment position 2 is the ground floor left rear sitting room french windows at the same house, 5.0 m from the unit behind a brick wall with no line of sight, and the calculated sound pressure level is 31.0 dB(A).
• Assessment position 3 is a first floor right rear bedroom window at 8 Grange Road, Chester, 15.0 m from the unit past a slatted fence with full line of sight, and the calculated sound pressure level is 31.5 dB(A).

All three use the same 60 dB(A) sound power level and the same Q4 directivity for a unit against the ground and one wall. The nearest position, at 5.0 m, returns the lowest figure of the three because the brick wall blocks the line of sight entirely and earns the full 10 dB. The furthest, at 15.0 m, gets nothing for the slatted fence and still passes on distance alone.

The rules are different in all four nations

England's legislation names one issue of one standard; Scotland and Northern Ireland both accept MCS Planning Standards or equivalent standards; and gov.wales says Welsh rights were updated on 1 June 2026 and now require MCS 020(a). Check the nation you live in rather than the first guide you read, and read these limits alongside the rest of the planning picture in our guide to heat pump planning permission.

England. Class G of Part 14 of the 2015 Order allows the installation, alteration or replacement of a microgeneration air source heat pump on a dwellinghouse or block of flats, or within its curtilage. Paragraph G.1 states that development is not permitted unless the air source heat pump complies with the MCS Planning Standards. Among the limits in paragraph G.2: no more than one unit on a dwellinghouse which is not detached or on a block of flats, no more than two on a detached dwellinghouse, an outdoor compressor unit volume not exceeding 1.5 cubic metres on a dwellinghouse or 0.6 cubic metres on a block of flats, nothing on a pitched roof, nothing within 1 metre of the external edge of a flat roof, and nothing on a listed building or a scheduled monument. In a conservation area or World Heritage Site it cannot go on a wall or roof fronting a highway; elsewhere it cannot go on a wall fronting a highway above the level of the ground floor storey.

Three of those rules changed on 29 May 2025. Article 5 of the 2025 amendment order substituted 1.5 cubic metres for the previous 0.6 cubic metres on a dwellinghouse, raised a detached house from one unit to two, and omitted sub-paragraph G.2(e), which in the 2015 text had blocked any part of the heat pump being installed within 1 metre of the boundary of the curtilage. The same article omitted the words "or equivalent standards" from paragraph G.1 and inserted a new condition that the heat pump is not solely used for the purpose of cooling. The other conditions in G.3 still require siting that minimises the effect on the external appearance of the building and on the amenity of the area, and removal as soon as reasonably practicable when no longer needed.

Wales. Gov.wales states that permitted development rights for air source heat pumps were updated on 1 June 2026, and that for an air source heat pump to be compliant your installation must comply with MCS 020(a), which it describes as setting installation standards including assessment of sound impact on neighbours. The Welsh limits now read across to England's: up to two units if your home is detached and one if it is not, an outdoor compressor unit volume not exceeding 1.5 cubic metres, nothing on a pitched roof, and nothing within one metre of the external edge of a flat roof. Gov.wales also states the unit must be for heating, or heating and cooling, and cannot be a unit designed for the purpose of cooling only. Wales used to take a blunter approach. A Welsh Government written statement of 11 January 2024 described the permitted development rights then in force as requiring a minimum 3-metre distance from the neighbour's boundary, to reduce noise pollution potential.

Scotland. Planning circular 1/2024 sets out Class 6H, which permits an air source heat pump on a dwelling or within the curtilage of a dwelling. Its limits are stricter in some places and looser in others: no more than one unit on the same building or within the curtilage, no protrusion of more than 1 metre from the outer surface of an external wall, roof plane, roof ridge or chimney, nothing in a conservation area unless the unit is at ground floor level on the rear elevation, nothing forward of a principal or side elevation that fronts a road, no resulting structure exceeding 3 metres in height, and nothing in a World Heritage Site or the curtilage of a listed building. The circular states that a condition of those rights is that the equipment installed must comply with MCS 020 planning standards for air source heat pumps or equivalent standards.

Northern Ireland. Class G of Part 2 of the Schedule to the Planning (General Permitted Development) Order (Northern Ireland) 2015, as substituted on 4 July 2023, permits an air source heat pump within the curtilage of a dwellinghouse. It is not permitted if there would be more than one unit in the curtilage, if any part would be within 1 metre of the boundary of the curtilage of another dwellinghouse, if any part would sit forward of a wall facing a road that forms the principal or a side elevation of the original dwellinghouse, if the unit would exceed 3 metres in height, if it would go on a roof, or if it would sit within the curtilage of a listed building without consent. In a World Heritage Site or conservation area, no part may face onto and be visible from a road. The conditions require the unit to be used to provide heat within the curtilage, to be removed when no longer used, and to comply with MCS planning standards or equivalent standards, which the Order defines as the product and installation standards for air source heat pumps specified in MCS 020.

What to ask before the quote is signed

The sound calculation is the installer's job, and MCS treats it as enforceable. Paragraph 1.4 of MCS 020 a) says contractors shall be under a duty to ensure compliance in relation to any installation carried out as permitted development, that MCS may impose penalties or sanctions where an MCS contractor fails to do so, and that an installation which does not meet the standard may be subject to enforcement action by the local planning authority. Ask these four.

• Which windows did you treat as assessment positions, and did that include the first floor as well as the ground floor?
• What sound power level did you use for the proposed unit, and is it the ErP rated figure rather than the quiet mode one?
• What Q value does the proposed position give, and would moving the unit off the second wall change it?
• Can I have my copy of the completed calculation table before the install?

Step 8 is blunt about what happens if the sum will not come down: the heat pump is only permitted development if the calculated level is 37.0 dB(A) or lower at every assessment position, so one window over the limit is enough to take it out. Work the siting out alongside the other siting constraints in our guides to heat pump sizing and radiators and heat pumps, and price the result with our UK heat pump cost guide.

Frequently asked questions