Do you need planning permission for air conditioning?

Most home air conditioning in England goes in without a planning application, under the permitted development right for air source heat pumps. But that right carries a condition almost nobody mentions, and it is the one most likely to catch out someone buying air conditioning rather than heating: the unit must not be used solely for cooling [1]. A reversible system that heats as well as cools qualifies. A cooling-only air conditioner does not, and needs planning permission. Get that distinction right before you choose equipment, because it is easier to specify a reversible unit than to apply retrospectively.

The rules below also changed substantially on 29 May 2025, and a great deal of advice still online describes the older, tighter regime. This page reflects the position as it now stands in England.

The cooling-only trap

Permitted development for this equipment sits in Class G of Part 14 of the General Permitted Development Order, and it is written for air source heat pumps, not for air conditioners. The Planning Portal lists it plainly among the conditions: the air source heat pump must be "not used solely for cooling purposes" [1].

That sounds like a technicality. It is not, because it decides which side of the line your project sits on:

• A reversible air-to-air heat pump — the standard modern split system, which cools in summer and heats in winter — is an air source heat pump. It falls inside Class G, provided the other limits are met. The 2025 amendments were made partly to support exactly this: MCS records that the government's changes were intended to "support the rollout of air-to-air heat pumps that can also provide a cooling function" [2].
• A cooling-only unit is not a heat pump for these purposes. Class G does not cover it, and installing one externally will generally need planning permission.

Nearly every system a UK installer will quote you today is reversible, so in practice most homeowners are fine. The risk sits with cheap cooling-only equipment and with anyone who assumes "air conditioning is permitted development" without checking what they are buying. If you want the right on your side, specify a reversible system — see heating and cooling for why that is usually the better buy anyway.

What changed on 29 May 2025

The 2025 amendment loosened the regime considerably. If you are reading older guidance, these are the four things it will get wrong [2]:

The size change matters more than it looks. At 0.6 m³ a lot of twin-fan and larger multi-split condensers were outside permitted development. At 1.5 m³ most domestic outdoor units comfortably fit, which removes what used to be a common reason for an application on a multi-split project.

The full Class G checklist for England

Every one of these must be satisfied for the installation to be permitted development [1]:

• MCS 020(a) compliance. The installation must comply with the Microgeneration Certification Scheme planning standard for sound. This applies whether or not the installation is an MCS certified one [2] — it is a planning condition, not a badge.
• Volume. Not more than 1.5 m³ for the outdoor compressor unit including its housing on a house; not more than 0.6 m³ for a block of flats.
• Number. On a house that is not detached, or a block of flats, only the first installation is permitted development. On a detached house, the first two are.
• No existing wind turbine on the building or within the curtilage. Additional turbines or heat pumps beyond the limits need an application.
• Roofs. Installations on pitched roofs are not permitted development. On a flat roof, every part of the unit must be at least one metre from the external edge.
• Listed buildings and scheduled monuments. Permitted development rights do not apply within the curtilage of a listed building, or within a scheduled monument. This is absolute — see period homes.
• Conservation areas and World Heritage Sites. The unit must not go on a wall or roof fronting a highway, nor be nearer to any highway bounding the property than any part of the building.
• Everywhere else. The unit must not go on a wall above ground-floor storey level if that wall fronts a highway.

And the conditions: not solely for cooling; removed when no longer needed; sited to minimise visual and amenity impact [1].

Permitted development rights can also be removed by a planning condition, an Article 4 direction, or another restriction [1]. Article 4 directions are applied street by street and are common in historic areas, so a neighbour's installation is evidence of nothing about yours.

Flats are the big exception

The permitted development right applies to a house or a block of flats — but a block of flats must consist wholly of flats, and where it applies to a block, it is one installation for the block, at 0.6 m³ [1]. It is not a right that each leaseholder can exercise for their own unit.

In practice this means a flat almost always needs planning permission for an external unit, and separately needs the freeholder's or management company's written consent, which is a contractual matter entirely independent of planning. Start both conversations early — our flat guide covers the sequence, and systems without an outdoor unit covers the alternatives when neither consent is forthcoming.

Noise: what MCS 020(a) actually requires

The sound condition is where most borderline cases are decided. MCS 020 was split in 2025 into MCS 020(a) for air source heat pumps and MCS 020(b) for small wind turbines, with compliance mandatory for installations under permitted development from 20 September 2025 [2].

The calculation establishes the sound level at an assessment position — in broad terms, a neighbouring habitable room — and permitted development depends on it staying within 42 dB(A). The 2025 revision also clarified several things installers used to argue about [2]:

• What can and cannot count as a solid barrier (fences and walls that genuinely screen sound, as opposed to anything vertical).
• How to determine the assessment position.
• What counts as a reflective surface — which matters enormously in a narrow side return where sound bounces between two walls.
• The definition of a habitable room.
• A method for including up to two heat pumps in one calculation, matching the new two-unit allowance for detached houses.

Because the boundary rule is gone, the sound calculation now does the work that the 1m rule used to do crudely. That is better engineering and worse guesswork: a unit can legally sit against a boundary, but only if the numbers say so at the neighbour's window. Our noise guide explains what to specify, and the external unit guide covers siting.

England only — and building regulations are separate

The limits above are the England position. Scotland, Wales and Northern Ireland run their own permitted development regimes with different thresholds, and none of the figures on this page should be assumed to transfer. Check with the local planning authority; GOV.UK sets out the general position on when permission is needed in England and Wales [4].

Planning permission is also not the only approval in play. Building regulations apply independently — principally to the electrical work, to any structural opening formed for pipework, and to fire-stopping where pipes pass through compartment walls or floors. Permitted development says nothing about any of that. Our installation process guide sets out what a compliant job involves.

Finally, refrigerant work is restricted regardless of planning: only an F-Gas certified engineer may work on the refrigerant circuit, and that is worth verifying before you get to the planning question at all — see how to choose an installer.

Frequently asked questions

Do I need planning permission for air conditioning at home? Usually not in England, if the system is a reversible air source heat pump and all the Class G limits are met [1]. You will need permission for a cooling-only unit, for a flat in most cases, for a listed building, and wherever an Article 4 direction has removed the rights.

Does the 1 metre boundary rule still apply? No. It was removed on 29 May 2025 [2]. The MCS 020(a) sound calculation now governs how close a unit can sit to a boundary.

How big can the outdoor unit be? Up to 1.5 m³ including housing on a house, or 0.6 m³ for a block of flats [1]. That is a substantial increase on the previous 0.6 m³ limit for houses.

Can I have two outdoor units? On a detached house, the first two are permitted development. On a non-detached house or a block of flats, only the first [1].

What if my house is listed? Permitted development rights do not apply within the curtilage of a listed building [1], and listed building consent is required separately for works affecting its character. Treat this as a full application from the outset.

What about a conservation area? The rights survive, but the unit cannot go on a wall or roof fronting a highway, nor nearer to a bounding highway than any part of the building [1]. A rear or side position usually works.

Is a cooling-only air conditioner ever permitted development? Not under Class G, which is written for air source heat pumps and excludes equipment used solely for cooling [1]. Specifying a reversible system is the simpler answer.

Does permitted development mean I can ignore my neighbours? No. The siting condition requires you to minimise the effect on the amenity of the area [1], and the sound assessment is taken at your neighbour's position, not yours.

Check your position before you choose equipment

The planning question and the equipment question are the same question, and answering them in the wrong order is what creates problems. Tell us about the property and we will match you with one vetted installer who will survey it, produce the sound calculation, and tell you plainly whether you need an application: get an installer match.