Overview of how are star ratings calculated?

Star ratings have been developed to provide consumers with an easy way of comparing the energy efficiency of different models. In this context, energy efficiency is defined as the "energy service per unit of energy consumption". It is a simple and fair way of comparing the energy consumption of products that do a similar job.

If you think of an air conditioner, for example, a model's efficiency is the amount of cooling capacity per unit of energy it consumes. A similar way of measuring the "energy efficiency" has been developed for all labelled appliances. Looking at the energy alone is not all that helpful, as a big appliance will nearly always use more energy than a small one, because it is doing more work. A measure of energy efficiency means that you can directly compare a great range of products.

The star rating system has a minimum of 1 star and a maximum of 6, shown in half star increments. Various "algorithms" or equations have been developed to rate the least efficient products at around 1 star.

If appliance energy efficiency in the market never changed, the stars could be adjusted so that the best products on the market now rated 6 stars. But we know from experience that manufacturers work hard to improve their products and over time, star ratings gradually improve. So when the stars were re-graded in 2000, it was necessary to leave some room for improvement. Hence under the current system, the most efficient products are generally only 3 or 4 stars (although there are some products that rate nearly 5 stars already for some appliance types).

Detailed star rating equations

The star rating equations for most products are fairly complex. However, if you are interested in the mathematics of how it is done, the technical details are contained in the document "Equations for Appliance Star Ratings". This document shows the star rating algorithm equations for refrigerators and freezers, dishwashers, clothes washers, clothes dryers and air conditioners. Equations for the old system (pre-2000) and for the current star ratings (from 2000) are provided for information. It also has information of star ratings for gas appliances. Changes to the algorithms for refrigerators and freezers and air conditioners are sheduled to change again in 2009 and details will be included when they are finalised.

More information of star ratings for other products

How are refrigerator and freezer star ratings calculated?

How are clothes washer star ratings calculated?

How are clothes dryer star ratings calculated?

How are dishwasher star ratings calculated?

How are air conditioner star ratings calculated?

This page last modified 28 June 2007