Do you need planning permission for air conditioning?

What changed, and when

Two separate reforms landed fourteen months apart and pull in opposite directions, which is why summaries of this go wrong. The first loosened the physical constraints considerably. The second replaced them with a single, stricter acoustic test.

The practical effect is that placements which used to be illegal are now fine, and placements which used to pass on paper now don't. Anyone working from a 2024 checklist will get both halves wrong.

The 37 dB test, in plain terms

This is the condition that decides most jobs, so it's worth understanding what it actually measures. It is not a limit on how loud the unit is. It's a limit on how loud the unit is at your neighbour's house.

The assessment point is one metre from every door and window of a habitable room in a neighbouring property — a bedroom or living room, not a garage or a bathroom. The figure is an LAeq, an average over a period rather than a peak, and it must come out at 37 dB(A) or below with the unit running.

A modern outdoor unit at 1 metre

45–50 dB(A)Manufacturer figure, measured in free field

The limit at the neighbour's window

37 dB(A) LAeqMCS 020(a)

Roughly what you have to lose

8–13 dBAchieved through distance, orientation and barriers

Distance that buys you 6 dB

Doubling itSound falls off with distance from the source

Because sound drops roughly 6 dB every time the distance doubles, small changes in position have large effects on whether a job is legal. Moving a condenser from three metres to six metres from a neighbour's bedroom window is worth about as much as buying a significantly quieter unit — and costs a few metres of pipe instead.

• Distance to the nearest neighbouring habitable-room window, which does most of the work
• Orientation — pointing the fan discharge away from the assessment point rather than at it
• Whether an existing wall, fence or outbuilding sits in the path
• Reflective surfaces: an inside corner between two walls can add several dB by bouncing sound back
• The declared sound power level of the specific unit, which varies more between models than most people expect

The cooling-only trap

This is the sharpest detail in the current rules and it catches people who think of the product purely as air conditioning. Air-to-air equipment falls within permitted development because it is heat pump equipment. A unit installed solely to provide cooling does not get that benefit.

In practice every reverse-cycle split we fit heats as well as cools, so the condition is satisfied by the equipment itself. But it does mean the heating capability isn’t a marketing angle you can take or leave — it is part of why the installation is lawful without an application. It’s also, separately, where most of the running-cost saving comes from; there’s more on that in what it actually costs to run.

When you do need permission

Permitted development rights are removed or restricted in a set of specific circumstances. If any of these apply to your property, assume an application is needed and budget time for it.

• Listed buildings — always, and listed building consent is a separate matter from planning permission
• Conservation areas, where the unit would be on a wall or roof slope fronting a highway
• National parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites
• Most central London boroughs, several of which have Article 4 directions removing these rights entirely
• Flats and maisonettes — householder permitted development rights don't apply, and there's usually a lease to deal with as well
• Any property where an earlier planning condition has already removed permitted development rights, which is common on newer estates

Scotland, Wales and Northern Ireland

England and Wales have moved; Scotland and Northern Ireland have not. The practical consequence is that the two things most commonly said about heat pump planning — that the 1 metre boundary rule is dead, and that the limit is 37 dB rather than 42 dB — are each true in exactly two nations and false in the other two. They are not the same two.

Wales — as of 1 June 2026, close to England

Wales made the same move fourteen months after England. The Town and Country Planning (General Permitted Development) (Amendment) (Wales) Order 2026 came into force on 1 June 2026: it removed the 3 metre boundary rule — Wales’s equivalent of England’s 1 metre rule, and stricter while it lasted — raised the volume limit to 1.5m³, and allowed a second unit on a detached house. It also names MCS 020(a) explicitly and deletes the old “or equivalent standards” wording, so the 37 dB calculation is the only route in Wales too.

Two Welsh conditions have no English equivalent and catch people out: the unit cannot go on a pitched roof at all, and on a flat roof it must sit at least a metre from the external edge. A block of flats is also held to 1m³ rather than 1.5m³.

Scotland — still 42 dB, and only one unit per building

Scotland’s rules sit in a different instrument entirely — Class 6H of the 1992 Scottish Order — and have not been amended since 24 May 2024. The order requires compliance with “MCS Planning Standards…or equivalent standards” without naming a version, and MCS’s position is that Scotland continues on MCS 020. So the limit in Scotland is 42 dB(A), not 37, and a page telling a Scottish reader otherwise is quoting England at them.

Scotland is more generous in one way and much stricter in another. There is no boundary distance requirement at all, and no volume limit — only a rule that nothing protrudes more than a metre from the wall or roof. But the unit cap is one per building rather than one per dwelling, which for a converted tenement or any block of flats means one unit for the entire building. In a conservation area it must be at ground floor level and on the rear elevation, and within the curtilage of a listed building or a World Heritage Site there are no rights at all.

A Scottish Government consultation has proposed moving to one unit per dwelling and setting a 1.5m³ limit for flats, with an instrument expected in early 2026. As at August 2026 no such instrument has been made, so the position above is the live one — but this is the section of this page most likely to go out of date, and it is worth re-checking rather than trusting.

Northern Ireland — where the 1 metre rule is still real

Northern Ireland is the one that reverses the headline correction on this page. The 1 metre boundary rule was never scrapped in Northern Ireland. Class G of the 2015 Order, as amended on 4 July 2023, still refuses permitted development where any part of the unit would sit within 1 metre of the boundary of another dwellinghouse’s curtilage. On a terrace or a narrow semi that is frequently the binding constraint, and it is the opposite of the position 100 miles away.

Northern Ireland also does not permit roof installation at all — the rights cover installation within the curtilage, and a roof position is expressly excluded — caps the external unit at 3 metres in height, and allows one unit per curtilage. In a conservation area or World Heritage Site the unit must not face onto and be visible from a road. Like Scotland, the noise condition is delegated to “MCS planning standards or equivalent”, which means MCS 020 and 42 dB(A).

What to actually do

1. 1Check whether your property is listed, in a conservation area, or has an Article 4 direction. Your local authority's planning map will tell you, free, in about five minutes.
2. 2Identify the nearest habitable-room window on each neighbouring property. That geometry, more than anything else, determines where the outdoor unit can go.
3. 3Get the sound calculation done for the specific position and the specific unit — not a generic assurance that the model is quiet.
4. 4Keep the calculation. It's the evidence that the installation was permitted development, and it's what you'll want if a neighbour complains or a buyer's solicitor asks.
5. 5If the calculation fails at every workable position, that's genuinely useful to know before you've paid for anything.

We run the calculation at survey and give you the result in writing, along with a drawing of the position it applies to. If it fails everywhere we’ll tell you that rather than fitting it anyway — which is the honest reason we’d rather survey before taking your money. That process is described in how it works.