Every air conditioner sold in Australia carries a star rating label, and most people glance at the number of stars without really knowing what’s behind it. Here’s what EER actually measures, how the star system works — and something almost nobody mentions: that rating only reflects reality if the system is running the way it was designed to.
What Is EER?
EER stands for Energy Efficiency Ratio. It’s a standard measure of how efficiently an air conditioner cools a space relative to the amount of electricity it consumes. In simple terms, it’s the ratio of cooling output divided by power input — the “energy service per unit of energy consumption.”
A higher EER means the unit delivers more cooling for the same amount of electricity. In Australia, EER figures for residential systems typically range from around 3 to 6, though manufacturer figures are usually converted into the more familiar star rating scale for consumers.
For heating performance in reverse cycle systems, the equivalent measure is COP — Coefficient of Performance. Both figures appear on the same energy rating label, usually as a blue label for cooling efficiency and a red label for heating efficiency.
How the Star Rating System Works
The Energy Rating Label is Australia’s national system for comparing appliance efficiency, mandatory on all single-phase, non-ducted air conditioners sold in Australia and New Zealand. The more stars shown, the more efficient the unit is relative to others of a similar capacity.
Since 2010, the scale extends to a maximum of 10 stars for genuinely high-efficiency models, shown with a separate “super efficiency” sticker alongside the standard 6-star label. Star ratings are only a fair comparison between units of similar cooling capacity — a 2.5kW unit and a 7kW unit with the same star rating aren’t delivering comparable value, since capacity output (measured in kW) tells you how much heating or cooling the unit can actually produce, separate from how efficiently it does so.
Ducted systems aren’t required to carry the label, though manufacturers can choose to publish EER and COP figures voluntarily — worth checking directly with the manufacturer or installer if you’re comparing ducted options.
What the Star Rating Doesn’t Tell You
This is the part that matters more than most people realise: the star rating on the label reflects the unit’s performance when it was tested new, under controlled laboratory conditions, with clean components and unrestricted airflow.
It says nothing about how that same unit performs three, five, or ten years into its life — particularly if it hasn’t been properly maintained.
Why a Dirty System Doesn’t Perform to Its Rated Efficiency
A 5-star air conditioner with a dirty filter, a grimy coil, and dust-clogged internals isn’t operating anywhere near 5 stars in practice — even though the rating hasn’t changed and the sticker is still accurate for a clean unit under test conditions.
A dirty filter restricts airflow across the coil — The system has to run the compressor and fan harder and longer to move the same amount of air through a partially blocked path, consuming more electricity to achieve the same result the label promised.
A dirty evaporator or condenser coil loses heat transfer efficiency — The coil’s entire job is transferring heat between the refrigerant and the air passing over it. A layer of dust and grime on the coil surface acts as insulation, working directly against that heat transfer, meaning the system needs more energy to move the same amount of heat.
Blocked or dirty outdoor unit components force the compressor to work harder — Debris, leaves, and dust around an outdoor unit restrict the airflow it needs to release heat effectively during cooling, degrading real-world efficiency regardless of what the rating label says.
A ducted system with dirty or leaking ductwork loses conditioned air before it reaches the room — Even a highly efficient indoor unit can’t deliver its rated performance if a meaningful share of the air it produces never actually gets where it’s going.
💡Pro Tip: If your electricity bills have crept up over a year or two with no change in how you use the system, and you own a high-star-rated unit, that gap between rated and actual efficiency — caused by maintenance neglect — is one of the first places worth checking.
The Real-World Impact of This Gap
Industry estimates suggest a poorly maintained air conditioning system can lose a meaningful share of its rated efficiency over time — sometimes enough that a 5-star unit performs closer to what a 3-star unit would when new. That gap translates directly into higher running costs, since the compressor and fan motor are working harder for the same cooling or heating output.
This matters more the higher the star rating on your unit, in a sense — a 6-star system that’s been neglected has more efficiency to lose than a 3-star unit did to begin with, meaning the financial impact of poor maintenance compounds with a more expensive, more efficient unit.
Quick Reference — What Affects Real-World Efficiency
| Factor | Effect on Efficiency |
|---|---|
| Dirty air filter | Restricts airflow, forces harder operation |
| Dirty evaporator/condenser coil | Reduces heat transfer, increases energy use |
| Blocked outdoor unit | Compressor works harder to release heat |
| Leaking or dirty ductwork | Conditioned air lost before reaching rooms |
| Low refrigerant | Reduces cooling capacity and efficiency |
| Regular servicing | Maintains efficiency closer to rated performance |
Keeping Your System Closer to Its Rated Efficiency
Check and clean or replace filters regularly — This is the single easiest maintenance step and the one that most directly restores airflow across the coil.
Have the coil professionally cleaned periodically — A coil clean removes the grime layer that’s actively working against heat transfer.
Keep the outdoor unit clear of debris — Leaves, dust, and vegetation growing too close all restrict the airflow the outdoor unit depends on.
Get ducted systems inspected if efficiency seems to be dropping — Duct leaks and buildup are a common, often overlooked source of lost performance.
→ Read more: Is Air Duct Cleaning Worth It? The Honest Answer for Perth Homes
The Bottom Line
The star rating on your air conditioner’s energy label tells you how efficient it was designed to be, tested under clean, controlled conditions. It doesn’t account for what happens after years of dust, grime, and neglect quietly erode that performance. A high star rating on a poorly maintained system is closer to marketing than reality — regular cleaning and servicing is what actually keeps a unit running near the efficiency printed on its label.
Star ratings look great on a showroom sticker, but they don’t account for what years of dust and neglect do to real-world performance. If your bills have been climbing and you’re wondering whether your system is still living up to what’s printed on its label, that’s exactly what a service inspection answers. We work across Perth, from Joondalup and Wanneroo in the north to Fremantle, Cockburn, and Armadale in the south.
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- Is Air Duct Cleaning Worth It? The Honest Answer for Perth Homes
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