Ranked by AEER
The cheapest split systems to run in summer.
AEER — annual energy efficiency ratio — is the amount of cooling a unit delivers for the power it draws, averaged across a year. Higher is cheaper. It is a finer measure than the star rating, because stars are banded: two units wearing the same number of stars can draw measurably different power for the same rated output.
Quick answer
On the Australian Government's GEMS register, the highest annual cooling efficiency figure among wall-mounted single-phase reverse-cycle models is AEER 6.25, held by the Mitsubishi Heavy Industries SRK20ZSXA-W (registration AAC8729), a 2 kW unit. Efficiency generally falls as capacity rises, so the leader overall is a small unit — the most efficient model in each size class is listed further down.
The ranking
Top 15 across every capacity.
Drawn from all 380 registered models, capped at three per brand so one manufacturer's range cannot fill the table. Efficiency generally falls as capacity rises, so a list ranked across all sizes leans towards smaller units — which is exactly why the per-size table below it is the one to buy from.
| Model | Cooling | Heating | Indoor noise | AEER | ACOP | Stars | Registration |
|---|---|---|---|---|---|---|---|
| Mitsubishi Heavy IndustriesSRK20ZSXA-W | 2 kW | 2.7 kW | 53 dB | 6.25 | 5.63 | 4.5 / 4 | AAC8729 |
| Mitsubishi Heavy IndustriesSRK20ZSXA-WF | 2 kW | 2.7 kW | 53 dB | 6.22 | 5.61 | 4.5 / 4 | AAC7747 |
| Mitsubishi Heavy IndustriesSRK25ZSXA-W | 2.5 kW | 3.2 kW | 55 dB | 5.56 | 5.33 | 4.5 / 4 | AAC8728 |
| DaikinFTXM25W2VMA | 2.5 kW | 3.2 kW | 57 dB | 5.3 | 4.95 | 5.5 / 3.5 | AAC6754 |
| DaikinFTXM25YVMA | 2.5 kW | 3.2 kW | 57 dB | 5.3 | 4.95 | 5.5 / 3.5 | AAC7604 |
| DaikinFTXM25AVMA | 2.5 kW | 3.2 kW | 57 dB | 5.27 | 5.57 | 5.5 / 4 | AAC10031 |
| TCLVAIH+3 variants | 2.8 kW | 2.65 kW | 47.73 dB | 5.11 | 5.54 | 5 / 3.5 | AAC8101 |
| TCLIH+5 variants | 2.8 kW | 2.65 kW | 47.7 dB | 5.11 | 5.54 | 5 / 3.5 | AAC8485 |
| Mitsubishi ElectricMSZ-LN25VG2B+3 variants | 2.5 kW | 3.2 kW | 54 dB | 5.07 | 5.3 | 4.5 / 3.5 | AAC8757 |
| Mitsubishi ElectricMSZ-LN25VGDB+6 variants | 2.5 kW | 3.2 kW | 54.5 dB | 5.07 | 5.3 | 4.5 / 3.5 | AAC9264 |
| Mitsubishi ElectricMSZ-LN25VG2B+6 variants | 2.5 kW | 3.2 kW | 54 dB | 5.07 | 5.3 | 4.5 / 3.5 | AAC8755 |
| Carrier42QAG026N8 | 2.65 kW | 2.75 kW | 55.28 dB | 4.98 | 5.16 | 6 / 3.5 | AAC7705 |
| Carrier42QHG026N8-1 | 2.65 kW | 2.75 kW | 55.28 dB | 4.98 | 5.16 | 6 / 3.5 | AAC6982 |
| Carrier42QRG026N8 | 2.65 kW | 2.75 kW | 55.28 dB | 4.98 | 5.16 | 6 / 3.5 | AAC8021 |
| FujitsuASTH07KMCD | 2 kW | 2.8 kW | 55 dB | 4.97 | 4.8 | 5 / 3.5 | AAC7486 |
Cooling and heating are rated capacity. AEER andACOP are the annual efficiency figures for cooling and heating — higher is cheaper to run. Stars are shown as cooling / heating for a mixed climate zone, which is the one Melbourne sits in. Indoor noise is the manufacturer's declared sound level for the indoor unit. Every figure is as registered with the Australian Government's GEMS register, and the registration number is there so you can look it up yourself.
The useful cut
Cheapest to run in each size class.
Nobody buys the best unit in Australia. They buy the best one that fits the room. This is the same ranking applied inside each capacity class, so you can start from the size you need.
Read this before you decide on it
What the figure does not tell you.
Efficiency figures are ratios, not running costs, and they are measured under standard test conditions. What a unit actually costs you depends on your tariff, how many hours it runs, what temperature you set and how well the room holds it — a highly efficient unit in a poorly insulated room will still cost more than a mediocre one in a well-sealed one. Use these figures to compare units against each other, not to predict a bill.
All figures are read from the GEMS registration database (Australian Government) and each model carries its registration number, so any line above can be checked atthe register. Rankings change when manufacturers register new models.
Compare another way
Cheapest to run air conditioners — common questions
What is the most efficient split system air conditioner in Australia?
On the Australian Government's GEMS register, the highest annual cooling efficiency figure among wall-mounted single-phase reverse-cycle models is AEER 6.25, held by the Mitsubishi Heavy Industries SRK20ZSXA-W (registration AAC8729), a 2 kW unit. Efficiency generally falls as capacity rises, so the leader overall is a small unit — the most efficient model in each size class is listed further down.
Is AEER better than the star rating?
It is finer. Star ratings are deliberately banded so shoppers can compare at a glance, which means a range of efficiency figures maps onto the same number of stars. AEER is the underlying ratio, so it separates two units that look identical on the sticker. Both come from the same registration, and both are published for every model sold in Australia.
Does a more efficient unit pay for itself?
That depends on how much you run it, and it is a calculation worth doing rather than assuming. A unit that runs a few weeks a year in a spare bedroom will take a very long time to recover a price difference through efficiency alone; a unit running most of the year in a main living area is a different case entirely. In Melbourne the heating figure usually drives that maths more than the cooling one, because the heating season is longer.
The spec sheet picks the unit. A site visit picks the install.
Where the head goes, whether the board can carry it and whether one unit or two suits the room are not on any register. Yiannis will tell you, free of charge — ARCtick certified, REC 28523.