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How can you find out where you are using your most energy?

With smart meters now almost ubiquitous among households and businesses, it’s easier to track your energy consumption day-to-day. However, these smart meters only tell you how much energy you are consuming in the property in total, not what in the property is consuming the most energy. So, how can you find out?

You could go around your house and unplug everything that’s switched on except for the device you wish to measure, then go and keep an eye on your meter with a stopwatch. You might have to wait and watch your meter tick for a while, however, so this method isn’t exactly efficient. It could, perhaps, be useful to measure the power of any devices where the plugs are difficult to reach, such as your oven or fridge, but even then, those items have inconsistent energy usage so you’d need to observe for a long time. There are other ways to measure, but before we get into that, it’s a good idea to understand how energy companies measure your consumption.

How do we measure energy usage?

It’s important to understand exactly how energy companies calculate your electricity bill. On the bill, there is a lot of information that can be quite difficult to understand, but the essential stuff that’s hidden in there is relatively simple.

Energy is measured in watts (W), but you’ll usually see it written as kilowatts (kW), which is 1000W. On your bill, the measurement they use is kilowatt-hour (kWh). Confusingly, this is not the same as kilowatts per hour. A kWh is a means of measuring how fast something consumes energy. If a device generates 1 kW of power and is on for an hour, it sustains 1 kWh of energy. If you switch on a 200W light bulb, it would take 5 hours to get to 1 kWh of energy. Most energy companies will measure your consumption using kWh.

Take a look at your electric bill. Take the total monthly cost – let’s say it’s £300 – and divide that by the total energy consumption – say, 2000 kWh. The result would be 300 ÷ 2000 = 0.15. And there you have your cost per unit – 15p per kWh. It’s worth doing this calculation even if you think you know the cost per unit.

A rough estimate

If specifics and accuracy aren’t too important for you, then there is a quick and simple way to find out what your devices are using. On the packaging or on the device itself there will be a piece of information that tells you the max power in watts.

Kettle Energy Details

If you take this figure, multiply it by the duration that it has been used in hours, and then divide by 1000, you’ll have your kWh! Albeit a rough and unreliable answer, but helpful for guidance on your appliances’ energy consumption. For instance, the kettle in our office says it uses 2520-3000W (kettles are notoriously power-hungry). Assuming we take the average amount of 2760W and it’s in use for 3 hours a day, we can make a rough calculation for the kWh:

2760 (watts) × 3 (hours) ÷ 1000 = 8.82 kWh

If we were to look at our energy bill or use the method in the previous section, we could check how much per kWh we are charged and calculate the daily running cost of our kettle. For instance, assuming our rate is 15p per kWh, the cost of our kettle would be 132.3p per day.

Keep in mind this method relies on appliances running at the wattage they have labelled, but this number is usually representative of the maximum. Most appliances use about half the shown figure.

Use an energy monitor

At time of writing, the most reliable technique for measuring your energy consumption is to get an energy monitor. These are devices that monitor the energy usage of an appliance when you plug that device in. One such device is the Kill A Watt Electricity Usage Monitor, but there are many other options. They come in a range of prices and the more you spend, the more reliable your reading will be (as a general rule, not always). Plug your device into the monitor, and then plug the monitor into the mains socket. The above example offers you readings on volts, amps, watts, and, most importantly, kWh.

Just make sure you’re aware of the appliance’s duty cycle. As we mentioned at the beginning of this blog, many items in your property will use varying amounts of energy throughout the day, such as your water heater or your fridge. The Kill A Watt comes with a timer in case you want to take a longer energy sample in order to account for varying electrical consumption.


Of course, statistically, heating or cooling the building uses the most energy, followed by your water heater: 61% of energy consumption in residential properties comes from these appliances. If your goal is to reduce energy usage in your building, then check out our blog on small measures that can save you money on your energy bill!


15 Dec 2017

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