An inverter air conditioner speeds its compressor up and down to match what the room needs, instead of running flat out and switching off. That makes it steadier and usually cheaper to run than the old on and off kind. Today, though, almost every split system on sale is an inverter, so the better question is which inverter, and that comes down to size, heating performance in Melbourne’s climate, and noise.
“Inverter” still gets printed on the box as if it were a premium feature. A decade or two ago it was. Now it is close to standard. CHOICE notes that inverter models make up the majority of air conditioner sales, with a few hundred split system inverter models on the market at any one time.
This guide explains what the inverter actually does, the habits that suit one, and the five things worth comparing once you know every option on your shortlist has one.
What the Inverter Actually Does
Every air conditioner has a compressor in the outdoor unit. It is the part that does the hard work and uses most of the power.
An older fixed speed air conditioner has one setting for that compressor: full. It runs at full output until the room reaches the set temperature, switches off, waits for the room to drift away from the setting, then starts again at full. Cold blast, nothing, cold blast.
An inverter changes the speed of the compressor instead. It runs hard at the start to bring the room down, then slows right down and keeps ticking over at whatever output holds the temperature. Daikin describes it as working “like the accelerator of a car, gently increasing or decreasing power”, so the set temperature is reached quicker and held without swings.
That has three practical results:
- The room stays closer to the temperature you set, without the warm and cold swings.
- It avoids the big surge of power every time a fixed speed compressor restarts, which is one reason inverters are usually cheaper to run.
- It is quieter most of the time, because it spends most of its hours running slowly.
Living With an Inverter: What Is Normal
Moving from an old system to an inverter, people are often surprised by how differently it behaves. Most of it is normal.
It Never Seems to Turn Off
That is the point. Once the room is at temperature, an inverter keeps running at low speed rather than stopping. The outdoor fan may turn slowly for hours. At that speed it draws much less power than it does at full output.
Constant Switching Works Against It
An inverter is at its best holding a steady setting. Switching it off every time you leave a room for half an hour, then asking it to pull the temperature back from scratch, makes it spend more time at full speed. Use the timer for long absences, and leave it running at a sensible setting for short ones. Our guide to what temperature to set in summer covers the setting.
Too Big Is Still a Problem
An inverter can only slow down so far. Each model has a minimum output, and a unit that is far too big for the room can still end up switching off and on in mild weather, like the old kind. Size still matters, which is the first item on the list below.
Five Things to Compare Instead
If every model on your shortlist is an inverter, these are what actually separate them for a Melbourne home.
| Compare | Where to find it | Why it matters |
|---|---|---|
| Capacity, in kW | Model name and spec sheet | Too small runs flat out. Too big cycles in mild weather |
| Heating stars for your climate zone | The Energy Rating label | Melbourne homes run reverse cycle for heating for months |
| Heating capacity in cold weather | Manufacturer spec sheet | Output drops as the outdoor temperature falls |
| Indoor noise level, in dB | Spec sheet, lowest fan speed | Matters most in bedrooms |
| Refrigerant | Spec sheet or outdoor label | Many new systems use R32 |
1. The Right Size
This decides more about comfort and running cost than any feature. A 2.5 kW unit suits a small bedroom, not an open plan living area. Our size calculator gives a starting point from the room’s size, and an installer should confirm it on site against the ceiling height, windows and insulation.
2. The Energy Label, Read for Your Zone
Newer air conditioners carry the zoned Energy Rating label, which shows separate cooling and heating ratings for hot, average and cold climates. The government’s guide to the label puts Melbourne in the cold zone. So the numbers that matter most for a Melbourne home are the heating stars on the cold zone part of the label, not the biggest number printed on it.
The government’s Energy Rating calculator fills in your climate zone from your postcode and estimates running costs for any registered model, which makes side by side comparisons easy.
3. Heating Output When It Is Cold Outside
A reverse cycle system pulls heat from the outside air, and the colder that air is, the less heat it can deliver. The spec sheet lists heating capacity at a standard test temperature, and some manufacturers also publish it at lower outdoor temperatures. If you plan to heat with it on frosty mornings, ask about this figure, and size the unit for the heating job. Our heat pump size calculator sizes for heating, and the gas to electric guide covers what reverse cycle heating costs to run in Victoria.
4. Noise
Spec sheets list indoor noise in decibels, usually at each fan speed. The lowest figure is the one you will live with at night. A few decibels is a noticeable difference in a quiet bedroom.
5. Refrigerant
Many new split systems use R32. It is worth knowing which refrigerant your system uses, because it decides what a technician needs if it ever needs gas. Our guide to air conditioner regas explains why an older R22 system is a different story.
Not Sure Which Inverter Suits the Room?
Tell us the room size, which way it faces and whether you want it for heating, cooling or both. We will recommend a size and a model and put the quote in writing.
Should You Replace an Old Non Inverter System?
Being a fixed speed unit is not a reason on its own. If an older fixed speed system still cools and heats well and is not costing much in repairs, there is no rule that says it has to go.
It is worth pricing a replacement when two or three of these are true:
- It is past about 12 years old, the typical split system lifespan our repair or replace calculator uses.
- It uses R22 and has started to need gas.
- It is loud, or struggles to hold temperature on hot days or cold mornings.
- You use it for heating through winter, where an efficient modern unit makes the biggest difference to the bill.
For a sense of the upfront cost, the split system installation calculator gives indicative ranges by size, and the running cost calculator shows what heating and cooling costs to run.
Questions About Inverter Air Conditioners
Is an inverter air conditioner worth it?
If you are buying new, you will almost certainly get one anyway, because inverter models make up most split systems sold. The more useful comparison is size, the heating stars for your climate zone and the noise level.
Do inverter air conditioners use less electricity?
Usually, because they slow the compressor down instead of switching it fully on and off. How much less depends on the model, the size and how you use it. The Energy Rating label and calculator give running cost estimates for specific models.
Why does my inverter air conditioner never turn off?
That is normal. Once the room reaches the set temperature, an inverter keeps running at low speed to hold it, rather than stopping and restarting. The outdoor fan may keep turning slowly.
Should I leave an inverter air conditioner on all day?
For short absences, leaving it running at a sensible setting usually suits an inverter better than switching it off and on. If the house will be empty for most of the day, turn it off or use the timer.
Are ducted systems inverters too?
Many ducted reverse cycle systems from the major brands use inverter compressors as well. Check the model’s specifications, and see our page on ducted reverse cycle air conditioning for how those systems work.
Comparing brands rather than features? Our guide to the best air conditioner brands in Australia and the Daikin vs Mitsubishi Electric comparison pick up from here.