Air conditioning is treated as an air source heat pump in planning law.
Class G says when you can install one without applying for permission. The
rule that catches most people is that a unit which only cools is never
permitted development, at any size, in any position.
Things that are not planning questions
All of these can stop an installation even when planning permission is not
needed.
Renting
You need your landlord's permission whatever the planning answer says. That is a tenancy question, not a planning one.
Leasehold
You need freeholder consent under your lease. This is separate from planning and is often harder to get.
Article 4 directions
A local authority can remove permitted development rights in a specific area. That is why the answer here is always to check with your local planning authority before ordering anything.
Building Regulations
They apply separately and are not affected by whether planning permission is needed.
F-Gas
Any work on the refrigerant circuit must be done by an F-Gas certified installer. That is a legal requirement about the engineer, not about the building.
The route that always works
A portable air conditioner needs no planning permission at all, because
there is no fixed external unit. That is the honest answer for renters,
for flats, for listed buildings and for conservation areas. It is worth
knowing before you spend anything on an application.
What changed in 2025
Class G, G.2(e). Omitted on 29 May 2025. This was the former one metre boundary rule. A unit may now sit against a boundary. Any site still
telling you a unit must sit a metre from the boundary, or that the
limit for a house is 0.6 cubic metres, is out of date.
Rules checked against legislation.gov.uk on 2026-07-30. Source: Town and
Country Planning (General Permitted Development) (England) Order 2015,
Schedule 2, Part 14, Class G, as amended by SI 2025/560.