The best temperature for your air conditioner

Set 24°C in summer. That is the whole trick. It sounds warm when it is 38 outside, and ten minutes after the room settles you will have forgotten the number entirely. Your body notices the difference between outside and inside, not the difference between 21 and 24.

Every degree colder costs roughly 5 to 10 percent more to run, because the unit has to hold a bigger gap against the heat coming through the walls. Chasing 20°C on a 40-degree day is how a 60-cent afternoon becomes a two-dollar one. Multiply by ninety days of summer and the thermostat is the most expensive dial in the house.

Winter is the same logic in reverse: 18 to 20°C is the efficient band. Every degree above 20 adds about ten percent, and a jumper is free. If the room feels cold at 20, check the draughts before you blame the unit — a gap under the door undoes a lot of kilowatts.

Two settings worth using. Sleep or quiet mode drifts the temperature a degree or two overnight and caps the fan, which saves money precisely when your body cares least. And the timer beats leaving it running all day for the dog — rooms recover in minutes, reputations for high bills take longer.

The honest footnote: none of this rescues a badly sized unit. An oversized system short-cycles at any temperature and a struggling undersized one never rests. Get the size right first, then argue about degrees. Our size calculator does the first half in a minute.

Want a number for your house? Check the rebate on your postcode. No name required. Check the rebate on your postcode.

Or do the sums yourself first: what size you need and what it costs to run.