The first step to saving electricity is usually to determine what devices in your home use the most energy. If you know your top 5 energy guzzlers you would know what changes will make the biggest difference.

The easiest way to do it is to use a plug-in power meter, similar to Kill-A-Watt.

Sometimes though it is not possible to use it. The device could be located in the hard to reach spot (e.g. whole house air conditioner). Or maybe you don’t have the meter handy.

What you can do in this case is to use your electricity meter, the one that counts how many kilowatt-hours you have used.

Recently I decided to measure how much electricity does our electric oven use. I suspect that it uses the most of the energy on weekends (that’s when my wife cooks).

I guess the oven is hard wired – I couldn’t find the socket for it in any case.

Here is our meter on the side of our house:

As you can see it is a smart meter. I live in Melbourne and we are lucky to get smart meters before the rest of Australia. The meter knows exactly how much energy our household is using right now but unfortunately it wouldn’t tell. All it shows is the total consumption so far and the current date and time.

However our meter has a little red blinking light. The more electricity we use, the more often it blinks. This is similar to the old meters with a spinning disk.

In fact there are two lights on our meter. According to the plate on the meter it turns the left LED lamp on or off every time 1 watt-hour is used. The right light is for var-hours.

So here is the plan:

- Calculate how much electricity our home is using with the oven off.
- Turn the oven on and calculate again.
- Subtract the first figure from the second figure. This will be how much electricity our oven use.

First, I counted beats with the oven off:

It was 4 beats in 38 seconds. This equals to 1 beat every 10 seconds on average. So every 10 seconds one watt-hour was used. Using this formula

watts = watt-hours / hours = watt-hours / (seconds / 3600 ) = watt-hours * 3600 / seconds

… we can calculate that this equals to 379 watts. Cool, we are using less than half kilowatt-hour per hour when the oven is off.

Next, I turned the oven on. I set the temperature to 200°C and the mode to ‘fan forced’. This time, I counted 32 beats in 20 seconds – this equals to 5,760 watts:

So based on that, our electric oven uses 5,381 watts or 5.381 kilowatt-hours per hour. At the moment we pay 40 cents per kilowatt-hour. So if we use our oven for 1 hour every day is would cost us $65 per month.

If you have an old analog electric meter you would count disc revolutions instead of blinks. Michael Bluejay has a great set of instructions and a calculator on his website that can help you.