When shopping for whitegoods and appliances, the energy star ratings can be a useful guide to judge the relative energy efficiency of different makes and models.
Be careful, though, because the stars can be misleading if you’re not comparing like-for-like.
For example, this week we were looking at chest freezers (we want to be able to buy meat in bulk and also freeze some of our garden produce). Most of the chest freezers available seemed to be 2.5 stars, which sounded pretty inefficient. So we looked at some upright freezers of a similar volume, and they were rated 3-3.5 stars.
I had always thought chest freezers were more efficient than uprights, but it seemed I was wrong.
I still didn’t really believe it, so I visited the Australian Government’s [Evergy Rating Database](http://www.energyrating.gov.au/appsearch/) to find out more. This database contains every model of every appliance that has been tested for an energy star rating in Australia and New Zealand.
We had been looking at a **Fisher and Paykel H220 chest freezer**, rated at 2.5 stars. According to the database, it uses 342 kWh/year of electricity. The **Fisher and Paykel N210 upright freezer** has the same volume and a 3-star rating, but it uses 498 kWh/year of electricity – 46% more than the equivalent chest freezer!
It turns out that all the different appliances are divided into different groups – chest freezers and upright freezers are in different groups (in fact there are 9 different groups for refrigerators and freezers alone!). Comparing stars across groups is completely invalid, because they are tested and calculated in different ways. The volume of the fridge or freezer is also part of the equation, so you can’t automatically assume a 3.5 star fridge uses less electricity than a 3 star one if they have different volumes.
So energy stars are only useful to compare two equivalent appliances. They must be the same type of appliance and have a similar volume for the comparison to mean anything.
The real measure you should be looking at is the number below the stars, showing the energy consumption per year of the appliance (measured in kWh). This will tell you exactly how much energy the appliance used under standardised testing conditions.
We’ll be using much less electricity with a chest freezer than even the most efficient upright in the database!