The planning rule that decides what air conditioning you can fit
In England a unit that only cools is never permitted development, at any size, in any position. One that also heats often is. Most sites miss this.
By David White
Air conditioning in England is treated, in planning law, as an air source heat pump. The rules live in Class G, Part 14, Schedule 2 of the General Permitted Development Order, and they were amended in May 2025.
One provision decides most cases, and it is the one almost nobody writes about.
G.3(aa)
The condition reads that the unit is not solely used for the purpose of cooling.
Read that again, because the consequence is large. A cooling-only air conditioner fails it. Not a large one, not a badly sited one: any of them, at any size, in any position. It is not permitted development and it needs a planning application.
A reversible unit, which is to say an air-to-air heat pump that heats as well as cools, passes. Same box, same refrigerant circuit, run in both directions. Everything else about the installation can be identical.
If you take one thing from this page: buy the reversible one. It is usually the same money or close to it, it removes a planning problem entirely, and it does something useful in February.
Terminology, because it causes real confusion
An air-to-air heat pump is a reversible air conditioner. It heats and it cools. This is the thing this page is about.
An air-to-water heat pump is the mainstream British type, feeding radiators and hot water. It heats only. It is a different product for a different job.
When somebody says “heat pump” in Britain they almost always mean the second. When an air conditioning installer says it, they almost always mean the first. The distinction is the difference between a permitted installation and a planning application.
What changed in May 2025
Two things worth knowing, because out of date guidance is everywhere.
The one metre boundary rule is gone. The former condition requiring the unit to sit at least a metre from the property boundary was omitted on 29 May 2025. A unit may now sit against a boundary. If a page tells you otherwise, it has not been updated in over a year.
The volume limit for a house is 1.5 cubic metres, including any housing. The 0.6 cubic metre figure still doing the rounds applies to a block of flats. Quoting the flats limit for a house is the single most common error in this subject.
The rest of the conditions
Permitted development is also lost on a pitched roof, on a flat roof within a metre of the edge, on a listed building or within its curtilage, on a scheduled monument, and in a conservation area or World Heritage Site where the unit is on a wall or roof fronting a highway or sits closer to the road than the building does. Outside designated areas, a highway-fronting wall is fine at ground floor level and not above it.
There are limits on how many units you may have: two on a detached house, one on anything else, including flats.
The planning permission tool walks all of it and tells you which specific provision catches you, with a link to the legislation so you can check the answer rather than trust it.
Things planning permission does not cover
Worth saying plainly, because people conflate them.
If you rent, you need your landlord’s permission whatever the planning answer is. If you are a leaseholder, you need freeholder consent under your lease, which is separate from planning and frequently harder. An Article 4 direction can remove permitted development rights in your area. Building Regulations apply either way. And any work on the refrigerant circuit must be done by an F-Gas certified installer.
None of those are planning questions. All of them can stop the job.
Questions
- Does this apply outside England?
- No. Wales, Scotland and Northern Ireland have separate regimes and nothing here can be read across to them. The tool states this on the page.
- Does a portable air conditioner need planning permission?
- No. There is no fixed external unit, so Class G does not apply at all. That is the honest route for renters, for flats, for listed buildings and for conservation areas.
- What size limit applies to a house?
- The outdoor compressor unit, including any housing, must not exceed 1.5 cubic metres. The figure for a block of flats is 0.6 cubic metres. Sites still quoting 0.6 for houses are using a limit that changed.
- Permitted development means I can just go ahead?
- Not quite. An Article 4 direction can remove permitted development rights locally, Building Regulations apply separately, and renters and leaseholders need permission from a landlord or freeholder regardless. Check with your local planning authority before ordering.