Do I need planning permission for air conditioning at my house?

This is the question people most often arrive here searching for, so it seems the right place to start the forum.

The short answer for a house in England is that it can be permitted development, and the trap is the one almost nobody mentions: the rules only allow a unit that is not used solely for cooling. A reversible unit, one that heats as well as cools, can be permitted development. A cooling-only air conditioner cannot, at any size, in any position.

The rest of the conditions are about where it goes and how big it is, and the planning checker walks through them one at a time and tells you which condition you fall foul of rather than just saying no.

Two things it deliberately does not cover: it is England only, and it assumes a house rather than a flat. Wales, Scotland and Northern Ireland have their own regimes and are not the same.

If you have been quoted for a cooling-only unit and told it needs no permission, that is worth going back to the installer about.

One thing worth adding, because it is what catches people out after the planning question is settled: permitted development is not the same as your freeholder or your management company saying yes. If you are in a flat, or on an estate with a covenant on the deeds, that consent is a separate conversation and it is the one that more often stops a job that was otherwise fine.

If anybody has been through this with their own council, what they actually asked you for would be worth posting here. The rules are national. How they get applied is not.