Saturday, 1 May 2010

What uses up the most electricity in your home or office? (calculator)

This is the question everyone has been asking and I too have been wondering.
I have created an “ElectricityUsageCalculator” (Excel spreadsheet) for you to calculate your usage and where you can make savings.
In fact, in the quest for the answer I have taken the long path of reducing my household’s electricity consumption and I thought that I’d share this information…
Before I get to the detail, I’d like to thank the following people/organisations/forums for sharing their valuable information:
Talk Radio 702 Power Guide:
Eskom’s Conserving Electricity page:
Saving Electricity 101:
Why not pay those sites a visit?

If you do want to save electricity/money try these steps (in the order listed):
*) turn down the temperature setting on your thermostat (mine is set to 40 degrees C) – you know when it’s set right by the amount of cold water that you need to mix when you’re having a shower…. If you’re mixing a lot of cold water, then you know that your thermostat is set too high – you need to turn it down (colder), until you are mixing no cold water (or little) in your shower.
See here: how to lower your geyser's thermostat
Heat loss will be small on modern (or geyser‑blanket clad) geysers and piping, but the lower the thermostat temperature, the lower the losses, and the lower the electricity that is used to get the water to the thermostat temperature.
Comment from Dave on “I turned my geyser down from 60oC to 50oC and saved 20% on my bill”
*) use less hot water (ie. Install a low‑flow shower head [I have an RST low flow one], and shower quickly) to save electricity – the less cold water that your geyser needs to heat up, the less electricity is used.
*) use the ‘Electricity Usage Calculator’ to see where you ‘spend’ your electricity.
Download from here: ElectricityUsageCalculator02.xls image
I was amazed to see that my main “culprit” was not my geyser, but in fact my swimming pool pump! [thanks Tim Truluck for pointing this out to me!]
Instructions for using the calculator:
Don't edit the shaded cells....
Step 1) In the worksheet ‘PerHourCosts’: check the ratings (W) listed [column D] and adjust to your appliances' ratings;
(Note which appliance is the most costly to run per hour)
Step 2) In the worksheet ‘UsageCosts’: fill in the 'hours used per item per month' [column D];
Note: 'Cost per item per month' - the high cost items is where you can save the most

*) Use solar power to heat your geyser: install solar panels. If you are building a new house or if you replace your geyser, then install solar panels and a time switch.  A solar‑only geyser will heat up the water more slowly (note: the thermostat plays no role in limiting the solar‑only upper temperature).  Installing a time switch in a solar installation will: 1) ensure that electricity is not used on a sunny day (i.e. on a sunny day you would rather have a slower heating up of the water by the sun, rather than use electricity and solar to heat up the water faster); 2) ensure that electricity is used so as to guarantee that there is hot water early in the morning and, in late afternoon on cold/cloudy days.
How do I find out how much electricity something uses?
Adapted from “Saving Electricity 101”:
Look at the label - nearly everything you can plug into the wall has a label that says how much electricity it uses.
If the label only gives the number of Amps and not the number of Watts, then just multiply the Amps by 220 to get the number of Watts. (Amps x Volts = Watts. So a hot plate that uses 3 amps uses 3 x 220 = 660 Watts.
Note that if a device is powered by a transformer (one of those great big plugs), then the transformer has converted the electricity from AC to DC, so you need to multiply by the DC voltage, not the AC voltage of 220. For example, if the device says "INPUT 9V, 0.5A", then that's 9 volts x 0.5 amps = 4.5 Watts.
Another tip:
*) Remember to turn off your ‘plug’ circuit breakers when you’re in “load-shedding” mode – this will ensure that your appliances are not connected to Eskom when power is turned on again – remember, when power is turned on again, there is usually a surge (over 220V) which could damage your appliances. Leave a light turned on, so that you know when power has returned, then turn your ‘plug’ circuit breaker back on again.

{Note: This HTT calculator is also available from the article “Does a time switch on your geyser actually save electricity?”}


  1. what about using your remote garage door as a front door instead of using the front door, that what we do, have been wondering if this uses a lot of elec

  2. Hi Anonymous,

    Don't worry, those motors don't use a lot of electricity. Worry about the wear and tear of the gears rather than the cost of the electricity ;)

    Save energy on the items that have a high wattage rating and that are on for a long time.

    Happy saving ;)

  3. Hi,

    I was wondering if you have an up to date calculator with the latest electricity pricing?


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