Check a heat pump against the 37 dB(A) noise limit

To be permitted development, the calculated sound level from the heat pump must be 37.0 dB(A) or lower at every assessment position. An assessment position is 1 m outside the centre of any window or door to a habitable room (bedroom, living room, dining room) of a neighbouring property. The level is calculated with the MCS 020 a) method, not measured on site.

Usually not, if the installation is permitted development. The main conditions are: it passes the MCS 020 a) noise calculation; the outdoor unit is no bigger than 1.5 m³ on a house (0.6 m³ on a block of flats); it is not on a pitched roof, or within 1 m of the edge of a flat roof; and there is only one unit, or two on a detached house. Listed buildings, conservation areas, World Heritage Sites and properties with an Article 4 direction have extra restrictions, so check with your local planning authority.

Yes. The rule that a heat pump had to be at least 1 m from the property boundary was removed in England on 29 May 2025. The noise calculation now does the work: a unit close to the boundary is fine as long as it meets 37 dB(A) at every neighbouring assessment position.

MCS 020 a) (Air Source Heat Pump Sound Calculation) is the planning standard named in the permitted development rules for England. Since the end of May 2026 it is the only accepted noise method for permitted development. It applies whether or not the installation is MCS certified, so homeowners and installers both need it.

Use the A-weighted sound power level (Lw or LwA) in dB(A) from the manufacturer: the product fiche, the energy (ErP) label or the MCS Product Directory. Do not use the sound pressure level, a figure "at 1 m", or a low-noise-mode rating. If the datasheet just says "noise level", ask the manufacturer which it is.

Move the unit further from the neighbouring windows, reduce the number of reflecting surfaces around it (for example, not in a corner), add a solid barrier that blocks line of sight, or choose a quieter model. If it still fails, the installation is not permitted development and you can apply for planning permission instead, usually with a noise assessment.

It can. MCS 020 a) gives a reduction for a solid barrier with no gaps that extends at least 1 m past each side of the heat pump. The reduction depends on how thick the barrier is and whether it fully or partly hides the assessment position from the top of the unit. Hedges, trellis and fences with gaps do not count.

Yes. Permitted development allows two air source heat pumps on a detached house. The calculator combines the sound from both units at each assessment position, as set out in Table 2 of MCS 020 a).

It is free. Everything runs in your browser: nothing you enter is uploaded, and your draft is saved only on your own device so you can come back to it.

No. The PDF records the MCS 020 a) calculation with the full workings so a planning officer, building control or your installer can check it. It does not grant planning permission on its own, and this tool is not produced or endorsed by MCS.