Split System vs Ducted Air Conditioning

Two different machines, not two price points

Ducted is often presented as the upgrade and split systems as the budget option. That framing gets people into the wrong system. They are different approaches to the same problem, and each is clearly better than the other in particular houses.

A split system conditions one space. It responds quickly, you only pay to cool the room you are in, and if it fails the rest of the house is unaffected. A ducted system conditions the whole house from one indoor fan coil, usually in the roof space, through insulated flexible duct to outlets in each room. It disappears into the ceiling, it is quieter in the living space because the noisy part is not in the room, and it handles a whole floor as one environment.

The real question is not which is better. It is which one your house and your habits actually suit.

What the Cairns roof space does to ducted

This is the part that gets glossed over locally. A Cairns roof cavity on a February afternoon is brutally hot, well beyond the outside air temperature. All of a ducted system’s air travels through that space, in duct, on its way to the rooms.

That makes duct insulation rating and, more importantly, duct sealing and layout into performance items rather than details. Air picks up heat on the journey, so a long run to a far bedroom arrives warmer than a short run to the lounge. Leaks at the collar are worse again, because a duct leaking into the roof cavity is not just losing capacity, it is dumping cooled air where it can never help you. Poorly executed ducted in this climate underperforms in exactly the rooms you notice at bedtime.

Done properly, with short well insulated runs, a sensible plenum layout and sealed joins, it works very well. The difference is entirely workmanship.

Zoning, part load and how each behaves overnight

Ducted zoning sounds like it saves money, and it does, up to a point. Run a large ducted system into a single small bedroom overnight and the compressor is being asked to modulate below the range it can usefully operate in. Older systems handle that by dumping surplus air back into the return through a bypass, which cools your roof space rather than your bedroom and keeps the system running at output you are not benefiting from. If most of your usage is one or two rooms at night, that pattern favours splits or a multi head system over ducted.

The reverse is also true. A house where the whole living area is used together, open plan, with several people in it, is where ducted stops looking expensive. Four or five separate splits doing the same work means four or five outdoor units, five sets of pipework, and five things to service.

Which one for which house

High set Queenslanders and older homes with no accessible roof space, VJ walls and no wall cavity often make ducted difficult or ugly, and splits or a multi head system placed thoughtfully are the honest answer. Newer slab on ground homes in the southern estates with a generous truss roof are natural ducted candidates.

Ducted is usually the better answer when:

• The roof space is accessible, has height, and has room for a fan coil
• The whole living area gets used together rather than room by room
• You want nothing on the walls
• There are enough rooms that the split count would climb past three or four

Splits or a multi head system are usually the better answer when:

• There is no usable roof space, or the house is high set
• Most of the running is one or two bedrooms overnight
• Rooms are used at very different times by different people
• You would rather one failure did not take the whole house with it

Read what is involved in ducted air conditioning in Cairns, or compare it against multi head split installation if one outdoor unit and several rooms is closer to how you live.