Do you need planning permission for air conditioning?

What changed in 2025

Until 29 May 2025, Class G carried a condition that the heat pump was "used solely for heating purposes", which shut out air-to-air systems. SI 2025/560 replaced it:

(aa) the air source heat pump is not solely used for the purpose of cooling;

The explanatory memorandum to that Order says the change will "allow for air-to-air heat pumps to benefit from the permitted development right". It also notes that the MCS noise standard applies to heat pumps that can cool.

The condition is about use, not the product

G.3(aa) is a condition on how the heat pump is used, and it lasts as long as the unit is there. A reversible system that heats the house in winter and cools it in summer meets it. The same unit used only to cool a room, with the house heated by something else, does not. That is a breach of condition, which the council can take enforcement action against.

The limits an air-to-air unit must meet

An air-to-air heat pump is treated as any other air source heat pump under Class G: see heat pumps for the full table. In short, for a house:

• it must pass the MCS 020 a) noise calculation, 37 dB LAeq,5mins at 1 metre outside a neighbour's habitable room window or door;
• the outdoor unit may be up to 1.5 cubic metres, one per semi-detached or terraced house and two per detached house;
• not on a pitched roof, and not on a listed building or within its curtilage;
• in a conservation area or World Heritage Site, not on a wall or roof fronting a highway, nor nearer a bounding highway than the house;
• elsewhere, not above ground floor level on a wall fronting a highway.

On a block of flats, Class G allows one heat pump for the whole block, with an outdoor unit of no more than 0.6 cubic metres. Where the block already has one, a flat owner fitting another needs permission: see flats and maisonettes.

A cooling-only unit

With no class to rely on, the question is whether fixing the unit to the house is development at all. Section 55(2)(a) of the Town and Country Planning Act 1990 says works that "do not materially affect the external appearance of the building" are not development. The smaller and less visible the unit, the stronger that argument, but the Act sets no size, so it is a judgement for the council. On a listed building, listed building consent is a separate requirement.

The permitted development checker takes you through the Class G tests for a unit that heats as well as cools.

Getting certainty

A lawful development certificate under section 192 of the Town and Country Planning Act 1990 confirms that a proposed installation would be lawful; the council has 8 weeks to decide. For an air-to-air system, include the MCS calculation and state that the system will be used for heating. For a cooling-only unit, a certificate is the formal way to settle the section 55 question in advance. See lawful development certificates.