Split system air conditioning in London

Air conditioning moves heat rather than making cold. Inside, a fan blows room air across a cold coil. The refrigerant in the coil picks up the heat and carries it through the pipes to the outdoor unit, where a compressor and a second coil release it outside. In winter many systems run the same cycle in reverse and bring heat in, which is why reversible split systems are also called air to air heat pumps.

Because the noisy compressor sits outside, the indoor unit is much quieter than a portable or all in one unit. Most modern units use an inverter, which means the compressor speeds up and slows down instead of switching on and off, so the temperature stays steady.

The indoor unit usually sits high on an outside wall so the pipes can go straight through. If the room you want to cool is at the front of a house in a conservation area, the pipes can run inside a ceiling void or a neat cover to a rear wall instead.

For the outdoor unit, we look for:

• a rear wall at ground floor level
• a flat roof at least 1 metre from the edge
• a lightwell or side return with good airflow
• a position away from neighbours' bedroom windows

Pipe runs of several metres are normal, so the two units do not need to be back to back.

Most new home split systems use R32, a refrigerant with a lower climate impact than the older R410A. Refrigerants are fluorinated gases, so the law controls who can handle them. The engineer must hold a personal F-gas qualification and work for a company certified by an approved body such as Refcom or the F-Gas Register. Ask for the company certificate number before you book and check it on the register.

For efficiency, look at the SEER (cooling) and SCOP (heating) ratings on the product label. Higher numbers mean more heat moved per unit of electricity. A correctly sized, well positioned unit will get closer to those figures than an oversized one that cycles on and off.

A single split is best for one room. If you want three or four rooms cooled, a multi split can run several indoor units from one outdoor unit, saving wall space outside. If you do not want any unit visible in the room, a ducted system hides in the ceiling. If there is nowhere for an outdoor unit at all, an all in one unit is the fallback. We explain the trade offs after seeing the property, and you can read more on our multi split and ducted pages.

A single split is usually the simplest install. Dust sheets go down, the indoor unit bracket is fixed and levelled, and one hole is cored through the wall with the dust extracted. The outdoor unit goes on wall brackets or a ground frame with anti vibration mounts. The copper pipes are flared or brazed, then pressure tested with nitrogen and evacuated before the refrigerant is released. The electrician connects the new circuit and isolator, and the system is run in cooling and heating. Before leaving, the engineer should show you the remote, the filters and how to keep the outdoor unit clear.