Ask most people building a house when they sorted out the air conditioning, and the honest answer is “near the end”. The slab goes down, the frame goes up, the cladding gets chosen, and cooling only comes up once someone notices there is nowhere obvious to put the unit. By then the easy options have quietly disappeared, decided weeks earlier by a wall here or a truss there. It does not have to go that way.
While the walls are open, running cable, planning duct routes and fixing the backing for a wall unit is straightforward. Once the plasterboard is on, all of it becomes a retrofit. So if you are building from scratch or putting up a kit home, treat cooling as part of the build, not a job for after handover.
Why the Cooling Decision Belongs at Design Stage
Adding air conditioning to a finished house is almost always the expensive, ugly version of the job. The ducting has to snake through a roof space nobody designed for it. The outdoor unit lands wherever there is a gap, not where it runs quietest. Cabling gets clipped to the surface because the walls are already sealed.
Do it during the build, and none of that happens. The installer has open cavities to work in, the electrician pulls the right circuit while the wiring goes in, and the outdoor unit can sit away from bedroom windows and off the boundary fence. Deciding early costs you a conversation. Deciding late costs you a compromise you will look at every day.
Start With the Building, Not the Unit
Before you shortlist a single model, look hard at the house, because how it is built decides how much cooling it needs. A room with west-facing glass will bake through a summer afternoon, and single glazing pulls in far more heat than double glazing. Insulation is the part nobody gets excited about and the part that matters most: seal well, and a smaller unit keeps the place comfortable; leave gaps, and you are buying a bigger system that works harder for the same result.
This matters most in a kit home, where the heating and the cooling are often locked in the same fortnight. Settle the insulation and glazing first; the cooling brief falls out of those choices.
Air Conditioners & Split Systems: Understanding Your Options
For most new builds it comes down to three families, and the fit depends on how many rooms you are cooling and how the plan is laid out.
A wall-mounted split system is one indoor head wired to an outdoor compressor, cooling a single room or open space. It is the workhorse of Australian homes: efficient, simple, and ideal for a bedroom, study or main living area.
A multi-split runs a few indoor units off one outdoor unit. Handy when you want separate control in several rooms but lack, or would rather not give up, the roof space full ducting needs.
Ducted does the whole house through discreet ceiling vents, with the indoor unit hidden in the roof. Zone it and you cool the living areas by day and the bedrooms at night, without paying to chill rooms nobody is in.
None of them wins outright; each suits a different house. If you are still torn, comparing a full range of Air Conditioners & Split Systems side by side is the quickest way to see how capacities and features stack up. And since the choice drives your duct planning and wiring, make it with the floor plan open in front of you.
Sizing Your System Correctly the First Time
Cooling capacity is measured in kilowatts, and the number matters more than people expect. Get it wrong in either direction and you will feel it.
Too small, and it runs flat out on the worst days and still never quite gets there. Too big is the sneaky one: a unit with capacity to spare cools the room in minutes, clicks off, then fires back up soon after. That constant stopping and starting has a name, short cycling, and it burns energy while wearing the system out faster than steady running would.
Right-sizing comes from the room dimensions, the insulation and glazing, and your climate, not from rounding up to be safe. This is what a licensed installer is for, and it is where those early envelope decisions pay off, because a tighter house needs less grunt to stay comfortable.
Building Energy Efficiency In From Day One
What a system costs to run is mostly locked in the day you buy it, not on the quarterly bill. The Zoned Energy Rating Label helps: blue stars for cooling, red for heating, scored across hot, average and cold climate zones, so you see how a model behaves where you actually live instead of on one national average. More stars, less power for the same comfort.
Reverse-cycle versus cooling-only comes down to climate. Reverse-cycle heats as well as cools, so it earns its keep anywhere with a proper winter; cooling-only suits the tropics, where you will almost never want the heat. Going ducted? Zoning is the biggest efficiency lever you have.
Bring In a Licensed Specialist Early
None of this replaces a proper assessment. Build type, orientation, insulation, how you will really use each room, these stack up in ways no rule of thumb catches. Get a licensed air conditioning specialist while the plans are still on screen, not after handover, so they can flag duct runs, outdoor-unit placement and wiring while it is all still easy to change.
Frequently Asked Questions
Should I Install Ducted or a Split System in a New Build?
It hinges on room count and roof space. Ducted suits whole-home cooling with zoning; a split or multi-split is the more economical pick for one or two rooms.
What Size Air Conditioner Do I Need?
Room size, insulation, glazing and climate decide it, and it is worth having a licensed installer work it out rather than guessing. Both extremes cost you: too small never keeps up, too big short cycles and wastes power.
Locking It In Before the Plasterboard Goes On
If you take one thing from this: put cooling on the list at design stage, right next to insulation and wiring. Settle the system type, have a specialist size it, and sort the duct routes and outdoor-unit spot while the cavities are open. It is a short conversation now. Skip it, and the alternative is cutting back into a home you have only just finished.
