Heat Pump Permitted Development: MCS 020(a) is now the only route

28 May 2026 was the last day you could lean on "equivalent standards". After it, permitted development for a heat pump in England rests on one thing: a completed MCS 020(a) noise calculation. There's no second route left.

What changed in Class G

The permitted development right for air source heat pumps sits in Class G of Schedule 2 to the planning order. Until last year it allowed a heat pump that met the MCS planning standards "or equivalent standards"  and those four words were the fallback. They let a manufacturer's noise figure or a third-party acoustic report stand in for the MCS calculation.

The 2025 amendment deleted them and named MCS 020(a) as the standard instead. It came into force on 29 May 2025 with a year's grace for work that was already permitted, and that grace ran out at the end of 28 May 2026.

The same amendment brought the changes you've been working with since: two heat pumps allowed at a detached house, one elsewhere, and a size cap of 1.5 cubic metres at a house, still 0.6 at a block of flats. Wales has since removed the same wording through its own order, though the conditions around it differ, so check those separately.

The PD noise limit is 37 dB, not 42

Here's the bit worth knowing. Plenty of quotes and inherited spreadsheets still work to 42 dB. That was the limit under the old MCS 020, and it came with a correction that gave you credit for background noise at the property.

MCS 020(a) does away with that. The figure you calculate must land at 37.0 dB(A) or below, full stop, no background allowance, no split between quiet rural sites and noisy urban ones.

Five decibels sounds like a rounding error. It's closer to two-thirds less sound energy. If your quoting template still says 42, it's quoting a limit that no longer exists.

What the Noise Calculation asks of you

Start with the unit. You need the sound power figure for the heat pump, which MCS publishes on its Product Directory for certified products. Not the sound pressure number off the brochure, different figure and only one of them belongs here.

Then work out what the site does to it. Three things move the number:

• Distance. Every doubling of the distance to the neighbour's window takes off roughly 6 dB.
• Hard surfaces beside the unit. Each reflecting surface adds about 3 dB. The ground counts as one, a wall behind the unit makes two, a corner makes three. More than three: a lightwell, say, can't be assessed under the standard at all, which means it isn't permitted development.
• A solid barrier. If it genuinely breaks the line of sight to the window, you can claim up to 10 dB back, and 10 dB is the ceiling. Solid means masonry, or a fence at least 18 mm thick. See the window over the top of it and you get nothing. Hedges and gappy panels never count.

Then test every position. The assessment points sit 1 m out from each door and window of a habitable room at the neighbouring properties. All of them must pass, and the worst one decides the job.

A worked example

Take a heat pump with a sound power figure of 58 dB on a rear wall, so ground and wall are both reflecting. The nearest neighbouring bedroom window is 6 m away, in clear view of the unit.

That comes out at 37.5 dB. It fails, barely, but 37.0 is 37.0. Three ways out of it:

• Move the unit out to 8 m and you're at 35.0 dB.
• Tuck it into a corner instead and you're at 40.5 dB, further from compliance than when you started. Corners are where borderline jobs die.
• Break the line of sight with a solid barrier and 37.5 becomes 27.5 dB.

What to keep on file

The calculation is your evidence that the job was permitted development, and you'll want it when a neighbour complains eighteen months later or a planning officer asks how you reached the figure.

Keep the signed calculation, completed before work starts, with a note of how you produced it, the paper method or the MCS spreadsheet tool, which covers two pumps under permitted development and four under full planning. Record where the sound power figure came from, every assessment position, how you decided which rooms were habitable, the surfaces you counted, and the barrier's type, thickness and line of sight. A single number at the bottom of a page isn't a record. The workings are.

If the noise calculation lives in a spreadsheet on one laptop while the heat loss, the design and the MCS compliance paperwork for the same job live somewhere else, that's the gap worth closing.

Book a demo today and we'll show you the calculation running alongside the rest of your job. Click the link below to get started.