If you want air conditioning in more than one room, you have two main choices. You can fit a separate single split system in each room, each with its own outdoor unit. Or you can fit a multi split, where one outdoor unit serves several indoor units. Both work well. The right choice depends on your house, how you use it and what you are prepared to see on the outside wall.
What is a single split?
A single split is one indoor unit connected to one outdoor unit by a pair of insulated copper pipes, a cable and a condensate drain. It is the simplest system there is. Each room is completely independent, and if one system ever has a problem, every other room carries on as normal.
What is a multi split?
A multi split connects two to five indoor units to a single outdoor unit. Each room still has its own remote control and its own temperature, but they share one compressor outside. The indoor units do not have to match. You can mix wall mounted units, slim ducted units hidden in a ceiling, and floor consoles on the same system.
How they compare
The outside of your house
This is usually the deciding factor in London. Three rooms on single splits means three outdoor units. On a terrace, a small balcony, a front elevation or in a conservation area, that can be a problem for looks, for neighbours and sometimes for planning. A multi split puts everything on one outdoor unit, usually at the back of the house.
Efficiency
Single splits are usually slightly more efficient per room, because each outdoor unit is matched exactly to one indoor unit. Multi splits are efficient too, but the outdoor unit runs at a less ideal point when only one small room is calling for cooling. For most homes the difference in running cost is modest.
Resilience
With single splits, one fault affects one room. With a multi split, a fault in the outdoor unit affects every room on it. Good equipment, a correct installation and an annual service keep that risk low, but it is a real trade off and worth knowing about.
Pipework
A multi split needs a pipe run from every indoor unit back to the one outdoor unit. On a tall house that can mean long runs and more trunking, so planning the route matters. Single splits can often go straight through the wall behind each indoor unit with very little visible pipework.
Cost
Costs depend heavily on the house, the pipe routes and the equipment. Sometimes a multi split is cheaper than the equivalent number of single splits, and sometimes it is not. A detailed site survey and a written quote for both options will show you which is right for your property.
When a single split makes sense
- You only need one or two rooms, and the outdoor units can go somewhere discreet.
- The rooms are far apart, for example a loft bedroom and a garden office.
- You want each room to be completely independent.
When a multi split makes sense
- You want three or more rooms but only have space or permission for one outdoor unit.
- You care about how the outside of the house looks.
- The rooms are close together, so the pipe runs back to one outdoor unit are short.
Our recommendation
For a lot of houses the best design is a mix: a multi split for the bedrooms on one floor and a separate single split for a living space or garden room. That is why we survey before we quote. We will look at the rooms, the walls, the pipe routes and the outside of the property, and we will tell you which option we would choose if it were our own house, and why.
Written by Zakaria Sinjab, F-Gas Category 1 certified engineer and director of Zephyr Climate Ltd.
