22 May 2026 · 4 min read
Set the thermostat properly
24 to 25 degrees in cooling and 20 to 21 in heating is the comfortable, efficient band. Every degree lower in summer adds roughly 5 to 10 percent to running cost.
Setting 18 degrees does not cool the room faster. It just runs the compressor harder for longer.
Use zoning and run only the rooms you occupy
On a zoned ducted system, closing bedroom zones during the day can cut consumption substantially. Keep at least the required minimum zones open so the system has airflow.
In a split system home, close the door of the room you are conditioning.
Keep the system breathing
Dirty filters and a blocked outdoor coil are the two most common causes of a system that costs more and cools less. Rinse filters monthly in summer and keep plants, bins and fences at least half a metre clear of the outdoor unit.
Help it with the building
External blinds, awnings and shade on west-facing glass do more than any thermostat setting. Ceiling fans let you sit comfortably two degrees warmer, and sealing draughts under doors keeps conditioned air where you paid to put it.
Pre-cool in the late afternoon before the peak, and use the timer so the system is not running in an empty house.
Frequently asked questions
What temperature should I set my air conditioner in summer?
24 to 25 degrees is the sweet spot for Sydney homes. It keeps the room comfortable while letting the inverter run at low speed, which is where it is most efficient.
Is it cheaper to leave the air conditioner running all day?
For a home that is empty during the day, no. Use the timer to start it 30 minutes before you get home instead.
Do ceiling fans help?
Yes. Running a fan with the air conditioner lets you raise the set point by about two degrees for the same comfort, which is a meaningful saving over a summer.