Split system or ducted, which suits an Australian home?

This is usually framed as a budget question and is better framed as a usage question: how much of the house do you actually condition, and how often?

Split systems

• Much lower installed cost, and you can add them one at a time as budget allows.
• You heat and cool only the room you are in, which is inherently efficient.
• Each room needs an indoor head, and there are limits on how far the outdoor unit can sit from it.
• Multiple units mean multiple things to service and multiple wall penetrations.

Ducted

• One system, largely invisible, conditioning the whole house from a single controller.
• Needs roof or underfloor space for the ducting, which not every home has.
• Without zoning you pay to condition rooms nobody is in. Zoning is what makes ducted economical rather than an optional extra.
• Higher upfront cost and a bigger job to install.

The factor that outweighs both

Insulation and draught sealing change the running cost of either system more than the choice between them does. A poorly sealed, poorly insulated house will be expensive to condition whatever is installed, and money spent on the building envelope generally returns more than money spent upgrading the unit.