Planning
Heat Pumps and Permitted Development: What Changed in 2025
The 2025 permitted development changes made air source heat pumps far easier to install across most of England. In prime London — conservation areas, listed buildings and flats — they change surprisingly little.
5 min read
What actually changed on 29 May 2025
For years, the biggest obstacle to installing an air source heat pump under permitted development was a single line in the rules: the outdoor unit had to sit at least one metre from the property boundary. On many London plots — narrow side returns, tight rear gardens, closely spaced terraces — that requirement alone pushed the job into a planning application. The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025, which came into force on 29 May 2025, removed it.
The same amendment widened the allowance in three further ways. The maximum size of the outdoor unit on a house rose from 0.6 cubic metres to 1.5 cubic metres — more than double, which brings larger and more powerful units within scope. Detached houses may now install up to two heat pumps under permitted development rather than one, opening the door to cascade arrangements for bigger properties. And the older heating-only requirement was relaxed, so systems that also provide cooling — provided they are not used solely for cooling — are no longer automatically excluded.
Taken together, these are genuinely useful changes for a standard suburban house with a garden. For much of England they make a heat pump a straightforward permitted development project. The question we are asked in prime London is a narrower one: does any of this help here? Often, the honest answer is that it changes very little.
The condition that replaced the boundary rule
Removing the one-metre rule did not remove the protection it was there to provide — neighbour amenity from noise. That protection now sits in a technical condition instead. Installations must comply with the MCS Planning Standards, and from 29 May 2025 the relevant standard is MCS 020 a), the air source heat pump sound calculation for permitted development installations, which replaced the earlier reference to MCS 007.
In practice this means the installer must run a sound calculation showing that the predicted noise level does not exceed the permitted development threshold — long set at 42 dB(A), assessed one metre from the nearest neighbour's habitable-room window — using the updated MCS methodology. If the calculation does not pass, the unit does not qualify as permitted development, however far it sits from the boundary.
This is where the relaxation and prime-London reality collide. Being allowed to place a unit right up against a party boundary is only helpful if the noise assessment still passes at the neighbour's window a few metres away. On dense London plots, the closer the unit sits to a shared boundary, the harder that calculation becomes — so the new freedom is frequently theoretical rather than practical.
Where permitted development stops: conservation areas
The 2025 changes did not touch the conservation-area restrictions, and those are what govern much of Hampstead, Highgate, Belsize Park and the wider prime market. In a conservation area, an air source heat pump cannot be installed under permitted development on a wall or roof that fronts a highway, and it cannot sit nearer to a highway that bounds the property than any part of the house. On a front-facing London plot with little or no side access, that often rules out every location a heat pump could realistically go.
There is a further layer that catches people out. Many of the streets where these homes sit are also covered by an Article 4 direction, which can withdraw permitted development rights that would otherwise apply. Where an Article 4 direction is in force, even an installation that would technically comply with the heat pump conditions may still need a planning application. The designation, not the equipment, is what decides the route.
None of this makes a heat pump impossible in a conservation area — it simply means the case has to be argued rather than assumed. A well-sited, well-screened unit with a robust noise assessment is very often approvable. It just goes through a full application, not the permitted development back door.
Listed buildings: permitted development does not apply
For listed buildings the position is simpler and more absolute: the permitted development rights for heat pumps do not apply at all, and the 2025 amendment did not change that. Any external unit, and often the internal alterations that go with it — pipe runs, a hot water cylinder, penetrations through historic fabric — will need to be assessed on its heritage impact.
In most cases that means listed building consent as well as planning permission, and the two are considered together. Listed building consent itself carries no application fee, but the work to support it is not trivial: a heritage statement, a considered location that avoids harm to the special interest of the building, and frequently a conversation with the conservation officer before anything is submitted.
We treat a heat pump on a listed building as a design problem, not a bolt-on. Where the plant goes, how it is screened, how services are routed to avoid scarring historic joinery or masonry — these decisions determine whether consent is granted, and they are far cheaper to resolve on paper than on site.
Flats and the leasehold layer
Blocks of flats do have permitted development rights for a heat pump — they held them before the 2025 changes, and those changes largely passed flats by. The conditions remain tight: the unit is capped at 0.6 cubic metres rather than the 1.5 now allowed on a house, only the first installation on a block qualifies, the building must consist wholly of flats, and the usual siting restrictions apply. For the mansion blocks and converted period houses that make up much of prime London's flatted stock, those conditions rarely all line up.
And permitted development is only half the story for a flat. Almost every flat is a leasehold interest, and the external walls, roof and structure are typically retained by the freeholder. Fixing a heat pump to an outside wall, running services through common parts, or occupying part of a shared garden usually needs the freeholder's licence to alter — a separate consent entirely from planning, and one the planning system cannot override.
So a flat owner can face the awkward position of a proposal that might satisfy the planning rules yet still cannot proceed without landlord consent, and often the agreement of a residents' management company as well. This is the point where the sequencing matters: establishing whether the lease and the freeholder will allow it at all, before any planning route is worth pursuing.
What a full application involves — and how we approach it
When permitted development does not reach — a conservation area frontage, a listing, a flat, or an Article 4 street — the fallback is a full planning application, and for many prime homes it is the right route rather than a setback. A householder planning application in England carries a statutory fee of £548 from 1 April 2026; listed building consent, where it is also needed, carries no fee, though it demands the heritage evidence to support it.
A sound application is built around the same technical spine as the permitted development test — an MCS-compliant noise assessment — plus the things designation adds: a considered siting that respects the street and the building, appropriate screening, and, where heritage is engaged, a statement that shows the impact has been understood and minimised. A short check of the solar and heat-pump permitted-development rules at the outset usually settles which route applies and whether the preferred location will pass on noise, before any fees are committed.
The 2025 changes are a real simplification for the majority of English homes. In prime London they are better read as a reminder of where the genuine constraints lie: not in the equipment, but in the conservation area, the listing and the lease. Those are exactly the questions worth resolving first — and they are the ones we spend most of our time on.
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