How does a multi-head work?
Instead of an outdoor unit for every room, one larger outdoor unit feeds several smaller indoor units through refrigerant pipes run through the ceiling rather than ducts. The ACT Government's guide calls it a hybrid of split and ducted that can serve several rooms almost as well as a ducted system.
The indoor units can be wall-hung, floor-mounted or cassette style, and you can mix them. Rinnai pitches multi-split at homes that need two to five rooms covered, each controlled separately, and Seeley says its Braemar multi split connects up to five indoor units to one outdoor unit. The limit depends on the model.
It works the other way round too. The ACT guide says a small multi-head can serve one very large room that needs more than one indoor unit.
The catch: every room shares a mode
Mitsubishi Electric says each indoor unit can sit at its own temperature, but all the units on one outdoor unit have to be heating, or all cooling. On a spring afternoon you can't cool a hot west-facing study while warming a cold bedroom on the same system.
The same brand's operating instructions advise against Auto mode on its multi outdoor units. With several rooms running, the system may not be able to swap between cooling and heating, and an indoor unit can drop into standby. Choose heat or cool yourself.
One outdoor unit is also one point of failure. If it stops, every room on it goes without until it's fixed.
Multi-head or separate splits?
| Multi-head | Separate splits | |
|---|---|---|
| Outdoor units | One | One per indoor unit |
| Heating one room, cooling another | No: all rooms share a mode | Yes: each unit runs its own mode |
| If the outdoor unit fails | Every connected room stops | Only that room stops |
| Efficiency in the ACT guide (CoP) | 3.7 average, 5.1 excellent | 3.7 average, 6.4 excellent |
| Who can install it | Full RAC01 licence holders only | RSS03 or RAC01, for single-head units under 18 kW |
| Suits | Neighbouring rooms, and little space outside | Rooms used at different times, or facing different ways |
Power, licences and VEU
The ACT guide says a multi-head in a large house may need an upgrade to three-phase power, because of how much it draws. Ask early, because it can change the job. Our page on the electrical side explains switchboards and circuits.
Only a full RAC01 licence holder can install a multi-head, and the ARC's restricted splits licence doesn't cover them at all. In Victoria the job is also plumbing work needing registration with the Building and Plumbing Commission, and the electrical work needs a registered electrical contractor.
VEU rules for multi-splits in Victoria changed on 30 September 2026, and a system of 10 kW or more now carries a larger minimum co-payment than a smaller one. Whether your job could qualify is for an accredited provider to tell you, and our VEU guide explains how the program works.
What to ask the installer
- Which rooms will share the outdoor unit, and how often will they want different modes?
- Where will the pipes run to the furthest room, and how will they be hidden?
- Can I mix a floor console or a cassette in with the wall units?
- Does the house need a power upgrade for this?
- Who on the job holds the RAC01 licence?
- If I add a room later, can this outdoor unit take another indoor unit?
What you can do, and what needs a licence
You can
- Pick heat or cool yourself rather than Auto, if your manual says so.
- Clean the filters in every indoor unit, not just the one you use most.
- Turn off indoor units in rooms nobody's using.
- Keep the outdoor unit clear of leaves and stored junk.
Leave to a licensed installer
- Sizing the outdoor unit for all the rooms together.
- Running refrigerant pipes through the ceiling, which needs RAC01.
- The power supply and any upgrade.
- Adding or moving an indoor unit later.
What we'd do
Where we'd start
If you want two or three rooms that sit side by side and outdoor space is tight, a multi-head is a tidy answer. If the rooms face different ways and you'll often want heat in one and cooling in another, we'd fit separate splits instead. Either way, ask for an installer who does multi-heads regularly, because the pipe routing through the ceiling is where these jobs go right or wrong.
