Home air conditioning installation in London

London is the hottest part of the UK in summer. The Met Office puts the average July daytime high at 23.5°C, the highest in the country, and both Heathrow and St James's Park reached 40.2°C on 19 July 2022, the joint UK record. The city also holds its heat after dark. Brick, stone and tarmac soak up sun all day and give it back at night, which is why a bedroom in Islington or Fulham can still feel stuffy at 2am when the countryside has cooled.

Most London homes were never built with cooling in mind. Victorian terraces have solid walls and slate roofs, mansion blocks have deep plans with little cross breeze, and many newer flats have large windows facing south or west. A split system lets you cool the rooms that matter, usually the bedrooms and a home office, without filling windows with portable hoses.

The indoor unit is the easy part. The real question in London is where the outdoor unit, sometimes called the condenser, can sit. Good spots are usually:

• a rear wall at ground floor level, away from a neighbour's bedroom window
• a flat roof over a rear extension, set back at least 1 metre from the edge
• a lightwell or basement area with enough air around it
• a garden on a low wall bracket or ground frame

Spots that cause trouble are front walls in conservation areas, pitched roofs, tight corners that bounce noise around, and balconies where the lease forbids fixings. The pipes between the two units can run several metres, so we can often keep the outdoor unit out of sight and still cool a front bedroom.

In England a heat pump used for heating, which includes a reversible air conditioner, can be permitted development under Class G if it meets the size, siting and noise limits, including a calculated 37 dB(A) at a neighbour's window under the MCS 020 planning standard. A unit used only for cooling is not covered, so it needs planning permission. Listed buildings always need consent, and in a conservation area the unit cannot go on a wall or roof facing the street. You can read the full list on the Planning Portal.

Three other rules matter. Anyone who installs or works on the refrigerant must hold an F-gas qualification and work for a company with F-gas certification from an approved body such as Refcom or the F-Gas Register, so ask for the certificate number and check it. The new electrical circuit is notifiable under Part P, so it must be done by a registered electrician or signed off by building control. If you own a leasehold flat, your lease will almost always need the freeholder's written consent before anything is fixed to the outside of the building.

A unit that is too small runs flat out and never quite cools the room. One that is too big switches on and off and leaves the air clammy. Sizing depends on the floor area, ceiling height, glazing, which way the room faces and whether there is a roof directly above. A top floor bedroom under an uninsulated roof needs more cooling than the same size room on the ground floor.

Noise matters on both sides of the wall. Inside, look at the quiet mode figure for night use. Outside, the council or your neighbours will care about the sound at the nearest window. In central boroughs the bar is high: Westminster's guidance asks for plant noise well below the existing background level. We pick the unit and the position together so the numbers work before anything is drilled.