Do you need planning permission for air conditioning?

What changed in May 2025

Permitted development rights let you do certain work without a planning application. The rights for air source heat pumps are in Part 14, Class G of the General Permitted Development Order. A 2025 amendment removed the old rule that a unit had to be a metre from the boundary, raised the size limit on a house and allowed a detached house to have two units. MCS, the certification body, confirms that air-to-air heat pumps can now use these rights as well, because air source heat pumps may also be used for cooling.

The conditions for a home in England

All of these must be met, according to the Planning Portal and the legislation:

• The unit is not used solely for cooling. A reversible system qualifies; a cooling-only one does not.
• The installation complies with MCS 020(a), the noise calculation. MCS says this applies whether or not the installation is MCS certified.
• The outdoor unit is no larger than 1.5 cubic metres on a house, or 0.6 cubic metres on a block of flats.
• A house that is not detached, or a block of flats, has only one air source heat pump. A detached house can have two.
• It is not on a pitched roof, and on a flat roof every part is at least a metre from the edge.
• Outside protected areas, it is not above ground-floor level on a wall facing a road.
• It is not within the grounds of a listed building or on a scheduled monument.

A planning condition or an Article 4 Direction can take these rights away, so a new-build estate or a protected street may be different.

The noise limit, and what it means for neighbours

MCS 020(a) sets a limit of 37 dB(A) at an assessment position 1 metre outside the centre of any door or window to a habitable room in a neighbouring property, and every position that could be affected must be checked. The sum uses the sound power of the unit, the distance, any barrier in the way and the hard surfaces around it. A unit tucked into a corner, with walls reflecting the sound, works out louder than one on an open wall.

Separately, the council can act on noise problems. Maidstone Borough Council says it may help with industrial and commercial noise and with machinery, and it asks people with neighbour noise to talk to the neighbour first. It is much easier to place the unit well at the start than to move it later.

Conservation areas in Maidstone

Maidstone Borough Council has 41 conservation areas. They include the town centre, All Saints, Ashford Road, Chillington House, Holy Trinity and Rocky Hill in Maidstone itself, and villages such as Bearsted, Boxley, Boughton Monchelsea, East Farleigh, Headcorn, Hollingbourne, Leeds, Lenham, Linton, the Loose Valley, Marden, Otham, Staplehurst, Sutton Valence, Teston, Wateringbury and Yalding.

In a conservation area, the unit must not go on a wall or roof that faces a road, and must not sit nearer to a road bordering the property than any part of the building. That rules out the front in most cases, and the side too on a corner plot. A rear wall or the back garden usually works.

Article 4 Directions

Some conservation areas have an Article 4 Direction, under which work that changes the outside of a building or its grounds may need planning permission. In Maidstone the council names parts of Headcorn, Eyhorne Street in Hollingbourne, part of Lenham, part of the Loose Valley and Maidstone Holy Trinity Church. If you live in one, ask the council before you plan anything, even at the back of the house.

Listed buildings

Permitted development rights do not apply within the curtilage of a listed building, so a planning application is likely to be needed for an outdoor unit in the grounds. Listed building consent is a separate matter and covers changes to the building itself, including holes for pipes. Doing the work without consent can be a criminal offence, so speak to the council's conservation officer first.

Business premises, flats and leases

Class G covers houses and blocks of flats. Shops, offices and other business premises fall outside it, so ask the council's planning team before ordering. Whatever the planning position, a flat or a rented property also needs the freeholder's or landlord's consent. That is a contract matter, and it is separate from planning.

If you are not sure

You can ask Maidstone Borough Council for a Lawful Development Certificate, which is formal confirmation that a proposal does not need planning permission. It is worth having if the position is borderline, and useful when you come to sell. This guide is a summary of the rules as we read them on the date above, not legal advice, and the council has the final word.