The main types
- Split system: a slim indoor unit on the wall, connected to an outdoor unit by a small bundle of pipes through a hole a few centimetres across. Quiet indoors and efficient
- Multi-split: one outdoor unit serving two or more indoor units. Useful when you want several rooms cooled but only have space for one unit outside
- Portable: a unit on wheels with a hose out of the window. No installation, but noisy, less efficient, and warm air leaks back in around the window. Fine for occasional use in one room
- Ducted: hidden in a loft or ceiling void, with grilles in each room. Usually part of a larger renovation
It heats as well
Most split systems sold now are reversible: they cool in summer and heat in winter. A reversible unit is an air-to-air heat pump, and it heats efficiently, giving out more heat than the electricity it uses.
It will not heat your hot water, so it does not replace a boiler. In the rooms it serves, though, it can do much of the heating for much of the year.
Who can install it
Connecting a split system means handling refrigerant, and by law that has to be done by an F-Gas certified engineer. The same applies to repairs and servicing that open the refrigerant circuit, and to recovering the refrigerant when an old unit comes out. Ask to see the certificate.
Most units also need their own electrical supply, which should be installed and certified by a qualified electrician.
Permissions
Whether an outdoor unit needs planning permission depends on the building, where the unit goes and your local council. A house is usually the simplest case. Flats, listed buildings and homes in conservation areas are more likely to need planning permission or listed building consent. We check before we quote.
If you own a leasehold flat, the outside walls and roof usually belong to the freeholder, so you will normally need their written consent, often a formal licence to alter, before anything is fixed to them. Check your lease before you get attached to a particular spot.
The practical details
- Condensate: in cooling mode the indoor unit produces water, which needs a route to a drain or outside, or a small pump. In heating mode the outdoor unit drips too
- Noise: indoor units are quiet, outdoor units hum. Site them away from bedroom windows, including the neighbours’, and use anti-vibration mounts. It saves an awkward conversation over the fence
- Pipe runs: the shorter and simpler the route between the indoor and outdoor units, the better
- Servicing: a regular clean and check keeps the unit efficient and the air it blows clean
Getting the size right
Size comes from heat gain, not floor area alone. A south-facing loft conversion with large roof windows can need far more cooling than a bigger room on a shaded ground floor. A proper survey looks at orientation, glazing, insulation, how many people use the room and what equipment runs in it.
An undersized unit runs flat out and never quite catches up. An oversized one cools the room too quickly, switches on and off, and leaves the air clammy, because it never runs long enough to take the moisture out.