Most people choose their indoor unit carefully and leave the outdoor unit to whoever turns up on the day. That is a mistake. Where the condenser goes affects efficiency, noise, servicing access, planning and the length and route of the pipework. On every survey we look at the outside of the property as closely as the room being cooled.
This guide covers the planning rules in England, noise, mounting options and the space a unit needs to breathe. It is general information: your council has the final say on planning.
Planning: permitted development in England
The Planning Portal explains when an air source heat pump on a house counts as permitted development, which means it doesn’t need a planning application. Since 2025 this covers air-to-air heat pumps as well as air-to-water. The main conditions include:
- the outdoor unit, including any housing, is no more than 1.5 m³;
- it complies with MCS 020(a), which includes a noise check (from 28 May 2026 MCS 020a is the only permitted scheme);
- it is not used solely for cooling;
- it is not within the curtilage of a listed building or on a scheduled monument;
- in conservation areas and World Heritage Sites, it is not on a wall or roof that fronts a highway, or nearer a highway than the building;
- elsewhere, it is not on a wall above ground floor level that fronts a highway;
- it is not on a pitched roof, and on a flat roof it is at least 1 m from the edge;
- detached houses may have two units; other houses one.
Flats and blocks of flats have different limits (0.6 m³), and an Article 4 direction can remove permitted development rights in some areas. A cooling-only air conditioning unit is not covered, so check with the council. Listed building consent is a separate matter again. Our planning permission guide goes into more depth.
Noise and neighbours
Modern outdoor units are quieter than older ones, but they still produce fan and compressor noise, and that noise travels. A good position:
- faces away from neighbours’ bedroom windows and gardens where possible;
- avoids enclosed corners and narrow passages that reflect and amplify sound;
- sits on proper anti-vibration mounts, so the unit doesn’t transmit hum through a wall;
- is not fixed to a thin or hollow wall that acts like a drum.
The MCS 020a check takes account of the distance to the nearest neighbouring window and any barrier in between. It is worth talking to neighbours before the work starts. Our noise guide explains how manufacturers quote sound levels.
Want it done properly? AirCon Doctor installs, repairs and services air conditioning and heat pumps across London and the South East, from our base in East Grinstead. We’re an F-Gas certified company and NICEIC approved. Get a fixed-price quote.
Wall brackets or ground mounting
| Wall bracket | Ground mounting | |
|---|---|---|
| Space | Keeps patios and paths clear | Needs a level base or stand |
| Vibration | Needs a solid wall and isolation mounts | Usually easier to isolate |
| Snow and leaves | Stays clear of ground debris | Raised feet help |
| Servicing | High brackets need safe access | Easy to reach |
| Security and knocks | Out of reach | May need a guard in busy areas |
Flat roofs are another option, subject to the planning rules above, structural checks and safe access for maintenance.
Airflow and clearances
An outdoor unit draws air through its coil and blows it out of the fan grille. If it can’t breathe, it recirculates its own discharge air, efficiency falls and, in a heatwave, it may cut out. Each manufacturer sets minimum clearances behind, beside and in front of the unit in that model’s installation manual, and those figures vary by model and by how many units share a space. We follow the manual for the exact model we fit, because that is also what the manufacturer’s warranty assumes.
As general rules:
- don’t box a unit into a tight alcove or fence it in on all sides;
- don’t point the fan straight at a wall, a hedge or another unit;
- avoid places where hot air collects, such as under a low canopy;
- leave room for condensate and defrost water to drain away, especially for heat pumps.
Pipe runs and the indoor unit
The closer the outdoor unit is to the indoor unit, the shorter the pipework and the neater the job, but the nearest wall isn’t always the best place. Each system has a maximum pipe length and height difference, set by the manufacturer. Longer runs may need extra refrigerant. Pipework can run on the outside wall in trunking, through a loft or within a ceiling void. We plan the route at the site survey and include it in the fixed-price quote.
Quick answers
Do I need planning permission for an air conditioning outdoor unit?
On a house in England, a heat pump that heats as well as cools can be permitted development if it meets the Planning Portal conditions. A cooling-only unit isn’t covered, so check with the council.
Can an outdoor unit go on a front wall?
Restrictions apply. In conservation areas it can’t be on a wall fronting a highway; elsewhere it can’t be above ground floor level on a wall fronting a highway.
How far from a neighbour can an outdoor unit be?
There’s no single distance. The MCS 020a noise check considers the distance to the nearest neighbouring window and any barrier.
Can I put the outdoor unit in the loft?
Standard outdoor units need outdoor air to work, so they are not designed for lofts. Some systems use indoor units with ducting instead.
Related services
- Air conditioning installation
- Air-to-air heat pumps
- Wall-mounted air conditioning
- Air conditioning in listed buildings
More advice
- Do I Need Planning Permission for Air Conditioning in the UK?
- Air Conditioning Noise: How Quiet Are Modern Systems?
- Air Conditioning Installation: What to Expect on the Day
- What Happens at an Air Conditioning Site Survey
- All advice
This guide is general information, checked against the sources linked on 30 October 2026. It isn’t legal, tax or financial advice. Rules, grants and product ranges change, so check the current position before you rely on it.