Air source heat pump permitted development rights in England were amended on 29 May 2025 by The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025 (S.I. 2025/560), which substituted the volume limits in paragraph G.2(d) of Class G, Part 14, Schedule 2 of the General Permitted Development Order1. The restated limits are 1.5 cubic metres for the outdoor compressor unit, including any housing, on or within the curtilage of a dwellinghouse, and 0.6 cubic metres for a block of flats1.
Class G covers the installation, alteration or replacement of a microgeneration air source heat pump on a dwellinghouse or a block of flats, or within the curtilage of either, including on a building within that curtilage1. The volume limits sit among the exclusions that determine whether a heat pump falls inside permitted development rights at all.
The same order made other changes to Class G. Paragraph G.1, which required compliance with the MCS Planning Standards, had those words omitted1. Paragraph G.2(a) was substituted, so development is not permitted if it would result in more than one air source heat pump on, or within the curtilage of, a dwellinghouse which is not detached, or a block of flats, or more than two on, or within the curtilage of, a detached dwellinghouse1. Paragraph G.2(e) was omitted, as was condition G.3(a)1. A new condition, G.3(aa), was inserted: the air source heat pump is not solely used for the purpose of cooling1.
Other exclusions in G.2 are unchanged in the text as published. Development is not permitted where a wind turbine is installed on the same building or within the curtilage, or where a stand-alone wind turbine is installed within the curtilage1. It is also excluded on a pitched roof, on a flat roof within 1 metre of the external edge, on a site designated as a scheduled monument, or on a building or land within the curtilage where the dwellinghouse or block of flats is a listed building1. In a conservation area or World Heritage Site, installation on a wall or roof fronting a highway, or nearer to a highway bounding the curtilage than the nearest part of the building, is excluded1. Elsewhere, installation on a wall fronting a highway above ground floor storey level is excluded1.
The remaining conditions require the unit to be sited, so far as practicable, to minimise its effect on the external appearance of the building and on the amenity of the area, and to be removed as soon as reasonably practicable when no longer needed1.
| Location | Outdoor compressor unit volume limit |
|---|---|
| Dwellinghouse, or its curtilage | 1.5 cubic metres |
| Block of flats, or its curtilage | 0.6 cubic metres |
Why it matters for households
The volume limit is one of the tests that decides whether a heat pump can go in without a planning application. A unit whose outdoor compressor and housing exceed the figure for the property type falls outside Class G, so a householder would need to apply for planning permission instead. The gap between the two figures is wide: a flat installation is capped at 0.6 cubic metres, less than half the dwellinghouse limit, which narrows the range of units that can be fitted under permitted development at blocks of flats. The limits apply to the outdoor compressor unit including any housing, not to the whole system.
The removal of the MCS Planning Standards reference from G.1 changes what the permitted development right itself requires, while the new condition that the pump is not solely used for cooling keeps the right tied to heating. The substituted G.2(a) sets out how many pumps are allowed by property type. Where a home sits in a conservation area, a World Heritage Site, or is listed, or where the installation would front a highway, separate exclusions apply, and in those cases permitted development may be withdrawn or unavailable. Scotland has its own size and location limits for air source heat pumps, and local authorities in England can remove permitted development through an Article 4 direction.
What happens next
The amendments took effect on 29 May 20251. No further dates are given in the published text.
Sources1 cited
- [](https://www.legislation.gov.uk/uksi/2015/596/schedule/2/part/14/crossheading/class-g-installation-or-alteration-etc-of-air-source-heat-pumps-on-domestic-premises/data.xht), legislation.gov.uk