Do inverter air conditioners use less power?

Usually, yes, because they spend most of their time running below full speed instead of stopping and starting. The saving depends on the unit being the right size for the room. An oversized inverter cannot slow down far enough and ends up cycling on and off like the old kind.

Is it better to leave an inverter air conditioner on all day?

Not all day in an empty house. Turn it off when nobody is home. When you are home, leaving it running at a steady setting is better than switching it on and off every hour, because an inverter uses the least power when it is ticking over rather than pulling a hot room down from scratch.

How do I know if my air conditioner is an inverter?

Check the model name, the rating plate on the outdoor unit or the manual. Most brands put inverter in the product name. Nearly every split system sold in Australia over the past decade is an inverter, so an older fixed-speed unit is usually one from before then.

Are inverter air conditioners noisier?

Usually quieter. Because they spend most of the time running slowly, the outdoor unit hums rather than roaring on and off. They also avoid the sudden start that makes an older unit clunk into life.

Air conditioning

What is an inverter air conditioner?

An inverter air conditioner changes the speed of its compressor to match how much cooling or heating the room needs. An older fixed-speed unit can only run flat out or stop. Almost every split system sold in Australia today is an inverter, so the word tells you less than it used to.

By Tania Elsafin5 November 20265 min read

The short answer

An inverter drives the compressor at variable speed, so it runs fast to cool a hot room and then slows right down to hold the temperature. A fixed-speed unit runs at full power until the room is cold, stops, then starts again when it warms. Nearly all new splits are inverters, so compare the energy label and get the size right rather than paying for the word.

How an inverter air conditioner works

The compressor is the part of an air conditioner that uses most of the power. In an older fixed-speed unit it has two settings: on at full speed or off. The thermostat switches it on when the room warms past the set temperature and off when it gets cold enough, so the room swings a degree or two either side and the compressor starts from a standstill many times an hour.

An inverter adds electronics that change the frequency of the power going to the compressor motor, which lets the motor run at a range of speeds. On a hot afternoon it runs near full speed to bring the room down. Once the room is close to the set temperature it slows down and keeps running gently, putting back only as much cooling as the room is losing.

Inverter vs non-inverter at a glance

	Inverter	Fixed speed
Compressor speed	Varies to match the load	Full speed or off
Room temperature	Steady	Swings above and below the setting
Starts and stops	Few	Many an hour
Power use in normal running	Lower, while it runs below full output	Higher
Noise	Quieter most of the time	Louder, with a clunk at each start
What you can buy new	Nearly every split system	Rare in splits today

When an inverter saves power and when it doesn’t

The saving comes from the slow running. Energy Rating, the Australian Government’s appliance efficiency program, notes that inverters now dominate the market and beat fixed-speed units over a season because most of the time a room needs only part of a system’s full output.

That only works if the unit is the right size. Every inverter has a minimum speed. If the system is far too big for the room, even its lowest speed puts out more cooling than the room needs, so it overshoots, stops and starts again, just like the old kind. It also runs cold air in short bursts that do little to dry the room. Our guide to what size air conditioner you need explains how to get that right.

A system that is too small has the opposite problem: it runs flat out all afternoon and never gets to slow down. Either way, the running cost depends on sizing and how you use it as much as on the compressor. The method for working out yours in kilowatt hours is in how much it costs to run an air conditioner.

What to compare instead of the word inverter

Because nearly every new split is an inverter, the useful comparison is the Zoned Energy Rating Label on the unit. It shows star ratings for cooling and heating across three climate zones and an estimate of the energy the unit uses each year in kilowatt hours. The NSW Government's air conditioner advice is simple: between two systems with the same stars and capacity, pick the one with the lower yearly energy figure.

Almost all of these are reverse cycle as well, which is a separate thing: reverse cycle means the unit can heat as well as cool and inverter means its compressor speed varies. Our guide to reverse cycle air conditioning covers the heating side.

Replacing an old fixed-speed unit

If your system is old enough to be fixed speed, it is probably also running on an older refrigerant and nearing the end of its life. Replacing it with a correctly sized inverter usually brings the running cost down and an eligible upgrade has the NSW Government discount taken off the quote. Our air conditioner replacement page explains how we size and quote it, and how long air conditioners last covers the signs it is time.

Common questions

Do inverter air conditioners use less power?: Usually, yes, because they spend most of their time running below full speed instead of stopping and starting. The saving depends on the unit being the right size for the room. An oversized inverter cannot slow down far enough and ends up cycling on and off like the old kind.
Is it better to leave an inverter air conditioner on all day?: Not all day in an empty house. Turn it off when nobody is home. When you are home, leaving it running at a steady setting is better than switching it on and off every hour, because an inverter uses the least power when it is ticking over rather than pulling a hot room down from scratch.
How do I know if my air conditioner is an inverter?: Check the model name, the rating plate on the outdoor unit or the manual. Most brands put inverter in the product name. Nearly every split system sold in Australia over the past decade is an inverter, so an older fixed-speed unit is usually one from before then.
Are inverter air conditioners noisier?: Usually quieter. Because they spend most of the time running slowly, the outdoor unit hums rather than roaring on and off. They also avoid the sudden start that makes an older unit clunk into life.