The short answer
Usually not in England, where air-to-air heat pumps that aren't used only for cooling count as permitted development if conditions on number, size, position and noise are met. Listed buildings, flats and protected areas follow different rules.
On this page
Most wall-mounted air conditioners sold for UK homes heat as well as cool, which makes them air-to-air heat pumps. In planning terms they come under the rules for heat pumps, which in England were changed on 29 May 2025, so advice written before then may be out of date. Everything in this guide applies to England only.
How permitted development works
Permitted development lets some kinds of work go ahead without a planning application, provided the work meets every condition that applies to it. For heat pumps, the conditions are set out in Class G of Part 14 of the General Permitted Development Order.
Nobody checks those conditions for you in advance. If an installation doesn't meet all of them, it isn't permitted development, and planning permission is needed.
One condition is specific to air conditioning: an air-to-air system must not be used solely for cooling. A system that heats the home and also cools it in summer can qualify. One used only for cooling isn't covered.
The main conditions in England
| Condition | What the rule says |
|---|---|
| Use | Not used solely for cooling |
| How many | One on a semi-detached or terraced house; two on a detached house |
| Size | Outdoor unit, including any housing, no more than 1.5 cubic metres |
| Roofs | Not on a pitched roof; on a flat roof, at least 1 metre from the edge |
| Walls facing a road | Not above the ground floor |
| Noise | Meets the MCS 020(a) noise standard |
A few of these need more explanation.
- Counting heat pumps. The limit is on heat pumps, not rooms. An air source heat pump already on the property, such as one that runs radiators, is likely to count towards it. A multi-split system runs several indoor units from one outdoor unit.
- Size. Outdoor units for home air-to-air systems are normally well under 1.5 cubic metres, but a cover or enclosure built around the unit counts towards the total.
- Distance from the boundary. Older guidance often mentions a rule that the unit had to be at least 1 metre from the boundary. That rule was removed in 2025. The noise standard still depends on how far the unit is from neighbours' windows.
- Walls facing a road. A unit can't go on a wall that faces a road if it would sit above the ground floor. On a corner plot, that can include a side wall. The rules actually say "highway", which usually includes public footpaths as well as roads.
- Noise. The installation must meet MCS 020(a), which limits the noise level at neighbours' windows. Noise rules and your neighbours explains how the calculation works.
Homes where the rules are different
Some homes can't rely on these conditions, or face stricter versions of them.
- Listed buildings. Permitted development doesn't cover them, and listed building consent is needed. See Listed buildings and conservation areas.
- Conservation areas and other protected areas, such as World Heritage Sites. The rules are stricter, including for units on walls and roofs that face a road.
- Flats. Flats follow different rules, so check with the local council. There are usually lease questions too, covered in Flats and leasehold homes.
- Homes whose permitted development rights have been removed, for example by an Article 4 direction or by a condition attached to an earlier planning permission.
If you're unsure whether any of these apply, your local planning authority, which is usually the local council, can tell you.
Getting certainty
When the conditions are met, planning permission isn't needed, but nothing on paper says so. A Lawful Development Certificate from the council provides that. You apply with details of the installation, and the certificate confirms that it doesn't need planning permission.
A certificate is optional. It can help where it isn't clear-cut whether a condition is met, and it's a straightforward document to show a buyer's solicitor if you sell later.
If the conditions can't be met, planning permission is needed, and the council decides on the application. Where permission was needed and not obtained, the council can take enforcement action, which can mean changing or removing the installation.
A good installer will check the conditions against your home before any work starts, and give you a copy of the noise calculation.
Wales, Scotland and Northern Ireland
Wales, Scotland and Northern Ireland each set their own planning rules. The conditions above don't carry across, so for a home in any of those nations, check with the local council before assuming a heat pump can be fitted without planning permission.
Related guides
- Noise rules and your neighboursIn England, a heat pump fitted without planning permission must be no louder than 37 dB(A) at 1 metre from a neighbour's nearest habitable-room window or door, worked out with the MCS 020(a) calculation. Councils can also investigate noise complaints separately.
- Listed buildings and conservation areasFitting air conditioning to a listed building needs listed building consent, and permitted development doesn't cover it. In England, conservation areas and other protected areas still have permitted development, but with stricter rules, including on walls and roofs facing a road.
- Flats and leasehold homesIn a flat or leasehold home, fitting air conditioning usually needs written consent from the freeholder under the lease, and the planning rules for flats differ from those for houses. Freeholder consent and planning are separate questions.
- Where the outdoor unit can goAn outdoor unit needs a firm fixing, free airflow, service access and somewhere for defrost water to drain. On a house in England it can usually go on a wall, the ground or a flat roof without planning permission if set conditions are met.