Air-conditioning planning and outdoor-unit siting

A fixed residential AC system has at least one outdoor unit. Its position affects planning, sound, airflow, pipe routes, drainage, appearance and future access.

Planning rules differ across the UK. The property type, designation, proposed position, number of outdoor units and whether the equipment heats as well as cools can all change the applicable route or conditions.

Planning position in England

Class G of the General Permitted Development Order provides a route for some domestic air source heat-pump installations in England. The current conditions include compliance with the referenced MCS Planning Standard and state that the equipment must not be used solely for cooling.

A reversible system is not automatically permitted development. The current English conditions also address matters including equipment volume, roof positions, highway-facing locations, listed buildings, scheduled monuments, external appearance and amenity. Planning conditions, Article 4 directions or other restrictions can remove permitted-development rights.

The transitional provision for work under the rules that applied before 29 May 2025 ended on 28 May 2026. The current assessment should use the legislation and MCS planning standard in force for the proposed work.

Scotland, Wales and Northern Ireland have their own planning frameworks. The English Class G conditions should not be applied to an address elsewhere in the UK.

Sound assessment

Manufacturer sound-pressure data is measured under stated test conditions and at a stated position. It is not a site sound assessment.

MCS 020 a) Issue 1.1 provides the calculation used by the current English permitted-development route. It assesses calculated sound pressure at every relevant assessment position against 37.0 dB(A) on the standard’s specified LAeq,5mins basis, ignoring the façade effect.

That figure belongs to this defined method. It is not a universal sound limit for every planning route, garden position or neighbour.

Airflow and service access

Outdoor siting affects airflow and the potential for discharged air to recirculate.

The position also needs service access and workable pipe, cable and drainage routes.

In heating mode, condensate and defrost water need to be included in the siting assessment.

Pipe and cable routes

The outdoor-unit position affects the routes for refrigerant pipework, cable and condensate or defrost water. These routes need to be established during the site assessment.

F-gas work

In Great Britain, work on stationary AC or heat-pump equipment containing F gas requires the appropriate individual qualification for the activity. A business that installs, repairs, maintains or decommissions equipment operated by others also needs the applicable company certification. This includes a sole trader working on customers’ systems.

F-gas qualification and company certification do not establish the planning position for the property.

Planning and siting evidence

For the chosen address and position, the relevant evidence includes:

• the planning route for the address and intended heating or cooling use
• property designations or restrictions
• outdoor-unit model and proposed position
• the applicable sound assessment
• airflow, recirculation and service access
• refrigerant, cable and condensate routes
• outdoor drainage in heating and defrost operation
• installer F-gas qualifications and company certification

Related entries

• MCS 020 heat-pump noise calculation
• Planning constraints for ASHP
• F-gas qualification rules
• Air-conditioning condensate drainage
• Single-split and multi-split air conditioning