Heat Pump Permitted Development: The 2025 Update
In May 2025, the government updated permitted development rights for heat pumps in England. The changes made it easier to install air source heat pumps without planning permission for most properties. The key requirements are: one heat pump (two on a detached house), an outdoor unit no larger than 1.5 cubic metres, no unit on a pitched roof, no unit on a conservation-area wall or roof fronting a highway or nearer a bounding highway than the house, and the unit must meet the noise limit of 37 dB(A) one metre outside any neighbour's habitable room window or door.
The noise limit is the critical one. Under the Microgeneration Certification Scheme (MCS) sound calculation MCS 020 a), every permitted development air source heat pump installation must be noise-assessed before installation to confirm it will meet the 37 dB(A) limit under the specific site conditions. This is not a theoretical limit — it is checked for your specific unit, your specific garden geometry, and your specific neighbours' layout.
How the Noise Limit Works in Practice
The 37 dB(A) limit is equivalent to a quiet office or library — not silent, but not disruptive. Modern heat pumps from manufacturers like Daikin, Mitsubishi, and Samsung are engineered to run well under this limit under normal conditions. A Daikin Altherma 3 R in heating mode at -7°C typically operates at 38-41 dB(A) at one metre from the unit, but the limit is assessed one metre outside a neighbour's habitable room window or door, not at the unit.
Problems arise in constrained gardens where the unit must be placed close to a boundary wall (which amplifies noise through reflection) or in back-to-back arrangements where two neighbours' kitchens face each other across a narrow passage. In these situations, we model the acoustic impact as part of our survey. If a standard installation would breach the limit, we can explore low-noise unit models, acoustic shields, or alternative siting positions.
Conservation Areas and Listed Buildings
In a conservation area, air source heat pumps on a wall or roof facing a highway are not permitted development — you need planning permission. Ground-mounted units that are no nearer a bounding highway than the house can retain permitted development rights even in conservation areas. If you are in a conservation area and want an air source heat pump, discuss siting options with us before the survey: a rear garden unit may be possible on permitted development.
Listed buildings require Listed Building Consent for any external heat pump installation that affects the character of the building. This is separate from and in addition to planning permission, which an air source heat pump on a listed building or within its curtilage needs because permitted development does not apply. The same principles apply as for solar on listed buildings: early pre-application engagement is essential, and rear or outbuilding siting is usually more viable than a prominent front elevation.
Ground Source Heat Pumps: Different Rules
Ground source heat pumps (GSHPs) do not have the same permitted development concerns as air source units, since the mechanical unit is usually inside the property. A microgeneration GSHP within the curtilage of a house is permitted development under Class C, and Part 14 attaches no specific limits to it. We complete a detailed site survey to confirm.
Ground source heat pumps are particularly effective on larger rural properties in East Anglia where garden or field space is available for horizontal collectors. They run quieter, operate more efficiently at low outdoor temperatures, and are often the preferred choice for rural Cambridgeshire and Norfolk properties converting from oil heating.
What Happens If Your Property Does Not Qualify for Permitted Development
Applying for planning permission for a heat pump is generally straightforward. The application fee is around £206, and decisions typically arrive within 8 weeks. Local planning authorities are generally supportive of heat pump applications given the UK's net zero commitments. The main grounds for refusal in residential areas are noise (which we design out from the start) and visual impact on conservation areas.
We submit planning applications on behalf of our customers where needed. The additional lead time is 8-12 weeks rather than the 2-4 weeks for permitted development installations. If you are on the BUS grant waitlist, we will flag the planning requirement so you can account for it in your timeline.
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