Multi-split heat pumps: room-by-room control explained
A multi-split air-to-air system connects one outdoor unit to several indoor units, each with its own controls, giving room-by-room heating and cooling with fewer units outside. The alternative is one outdoor unit per room.
The key points
- One outdoor unit, typically two to five indoor units
- Each room has its own controls and temperature
- Tidier outside, but one outdoor fault affects every room
- Plan spare capacity if you may add rooms later
- Units are sized room by room before a firm price
The short answer
A multi-split air-to-air system connects one outdoor unit to several indoor units, typically two to five, each with its own controls. It gives you room-by-room heating and cooling with fewer boxes on the outside of the house. The alternative is several single-split systems: one outdoor unit for each room.
How it works
The outdoor unit pumps refrigerant through separate pipe circuits to each indoor unit. Each room has its own remote or app control, so the bedroom can be cooling at night while the office is off. On most systems every room has to be in the same mode (all heating or all cooling) at the same time, which is rarely a problem in a home.
Multi-split or single-split?
| Multi-split | Several single-splits | |
|---|---|---|
| Outdoor units | One | One per room |
| Wall space and appearance | Tidier outside | More units on the walls |
| If the outdoor unit fails | All rooms affected | Only that room |
| Efficiency with one room running | Can be lower | Each unit matched to its room |
| Adding rooms later | Only up to the outdoor unit’s capacity | Add another system any time |
Planning ahead
If you might add rooms later, say so at the start. A multi-split can be sized with spare capacity and pipe routes planned now, which is far cheaper than changing course later. If you’re starting with one problem bedroom and may never do more, a single-split is often the sensible choice.
Getting the sizing right
Each indoor unit is sized for its room, and the outdoor unit for the combination. Oversizing wastes money and makes rooms cycle on and off; undersizing leaves a room struggling on the hottest or coldest days. That’s why sizes are confirmed room by room before a firm price.
See what affects the cost and running costs, or start your home assessment and tell us which rooms you have in mind.
Sources
Questions
Can different rooms be at different temperatures?
Yes, each indoor unit has its own setpoint. Usually all rooms must be in the same mode, heating or cooling.
Can I add rooms later?
With a multi-split, only up to the outdoor unit's capacity, so plan ahead. Single-splits can be added any time.
Is multi-split cheaper?
Often for three or more rooms, but it depends on layout and pipe runs.
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