Whole house
air conditioning

What decides the number

Which rooms are genuinely worth doing

Bedrooms first, and the main bedroom before any of them, because the difference between sleeping and not sleeping in a July heatwave is the whole reason most people call.

Then the room the household actually sits in during the evening, which is usually the living room or the kitchen diner. A kitchen diner is the hardest room in the house because of the cooking load and it is frequently the one that gets used most.

Then a home office, if somebody works in it every day. That is a comfort argument and also a productivity one, and it is the room where the running cost is easiest to justify.

What is rarely worth doing: landings, hallways, bathrooms, and a spare bedroom used six nights a year. Leaving three of those out of a five-room quote saves more than any amount of haggling, and the outdoor unit gets smaller as well.

One outdoor unit or two

A domestic multi-split outdoor unit typically serves up to five indoor units. Up to five rooms is one outdoor unit, one position to find, one thing for neighbours to look at and one electrical supply. Six or more means two, and the cost steps rather than sloping.

That step is worth knowing before you decide the room list, because five rooms and six rooms are not a linear difference in price. If the sixth room is a spare bedroom, leaving it out can save well over a thousand pounds.

There is a second consideration that catches people out. A large multi-split has a minimum output it can turn down to, and if you run one bedroom on its own at three in the morning while the other four are off, it can end up cycling. That is a sizing conversation at survey rather than a reason to avoid it.

Phasing it, and when that is the right call

Doing it in two phases costs more overall, because the second visit repeats the setup, the access and part of the labour. It is still frequently the right decision.

The way to phase it well is to size the outdoor unit for the final room count on the first visit and leave the ports for the rest. That costs a few hundred pounds extra now and saves a new outdoor unit later. Sizing it for phase one and adding rooms afterwards is how people end up replacing equipment that is two years old.

If there is a loft conversion or an extension coming, say so at the first survey. It is the cheapest information you can give us.

Doing it during a renovation

If the house is already being worked on, this is the moment. Pipe routes, condensate falls and the electrical supply all cost a fraction of what they cost once ceilings are closed, floors are down and rooms are decorated, and the positions available are better because nothing has been finished around them yet.

It also removes the internal-versus-external pipe route argument entirely, because everything can go internally through a floor void or a stud wall.

The trade-off is committing to the room list before living in the house. Where that is uncertain, running the pipework to a room and leaving it capped is cheap insurance.

What it costs

Every figure on this site is an estimate built from the quotations we issued in 2026 and our own installation experience. It is not a quotation. The price you are given after the free survey is the price you pay.

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