Short answer: For most houses in England and Wales, an outdoor unit can be fitted under permitted development if it meets size, number and noise conditions: up to 1.5 m³ for a house, no more than two units on a detached house or one on other houses, and a calculated noise level of 37 dB(A) or less at the nearest neighbouring window under MCS 020(a). Listed buildings, flats with more than one unit and pitched-roof installs need permission.
England
Rules changed on 29 May 2025. The old 1 m boundary rule was removed, the size limit for a house rose to 1.5 m³, and detached houses can have up to two units. Units must meet MCS 020(a) noise limits. Blocks of flats are limited to one unit of up to 0.6 m³. Listed buildings and scheduled monuments need permission, as do pitched-roof installs and flat-roof installs within 1 m of the roof edge. The updated rules also cover heat pumps used for cooling, which brings many air-to-air systems within them.
Wales
From 1 June 2026, Welsh rules were brought closely into line with England's: the old 3 m boundary rule was removed, the size limit rose to 1.5 m³, detached homes can have two units, and units must meet MCS 020a noise limits. Listed buildings need consent, and conservation areas have extra restrictions, such as no unit on a wall or roof facing a road.
Scotland and Northern Ireland
Permitted development rights for heat pumps and outdoor units exist in Scotland and Northern Ireland but with their own conditions, and listed buildings and conservation areas are treated more strictly. We check the current rules with you on survey and, where needed, help you contact the local planning authority.
Flats and conservation areas
Blocks of flats are more likely to need planning permission: in England, permitted development allows only one outdoor unit of up to 0.6 m³ on a block of flats. Homes in conservation areas may need permission for units on elevations facing a road. Leaseholders also need freeholder consent. We position outdoor units at the rear or on balconies wherever possible.
Related services
Sources
- GrantUK: Heat pump planning guide for England (March 2026)
- GrantUK: Heat pump planning guide for Wales (July 2026)
- Cooling Post: New planning rules boost heat pump access
More guides
- How much does air conditioning cost to install in the UK?
- How much does air conditioning cost to run?
- What size air conditioner do I need?
- Fixed split or portable air conditioning?
- The £2,500 grant for air-to-air heat pumps explained
- F-gas rules: what homeowners need to know
- R32, R410A and R22: refrigerants explained
- Is air conditioning the same as a heat pump?
- What happens on air conditioning installation day
- Air conditioning noise and your neighbours
- Looking after your air conditioning: an owner's checklist
- Can you fit air conditioning in a listed building?
- Air conditioning in a flat: leases, freeholders and planning
- Keeping a home cool in a heatwave
- Multi-split or separate single systems?
Reviewed October 2026. Rules and prices change; check the date and ask us if anything is unclear.