Friday, 14 March 2008

Does a time switch on your geyser actually save electricity?

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:
Why not pay these sites a visit?

Cutting to the chase:
OK, so some of you don’t really want to know how I got to the “findings”, you just want to know if turning your geyser off and on really saves you Rands, so here goes:
*) if you have a solar panels, then yes - installing a time switch on your geyser will definitely save you money (without time switch: electricity and solar will heat up the cold water, and so electricity will be used. With time switch: only solar will be used to heat up the cold water; electricity will kick in if the time switch is set to use electricity for critical time periods. See here for more details:
*) if you don’t have solar panels, then you’ll probably not save a lot of money by installing a time switch: Niel says (see comment on 6th February 2008 @ 10h08: that you’ll “only save electricity if you leave your geyser off for 2.5 days”; and “you can’t save electricity by switching a heater on and off, as the amount of energy required to keep it at a certain temperature for a given time and to heat it up again after that given time is the same.”
Again, referring to Niel's comment February 12th, 2008 at 1:01 pm: <> " geyser was on for 46 minutes over a 24hr period or basically for 1 minute 55 sec every hour..." <>
….rather insulate your geyser (using a geyser blanket) and hot water pipes to reduce the heat loss.
….but if the time switch is set to turn the geyser off during peak times, then you will help Eskom to reduce the peak loads and perhaps reduce the need to load-shedding…. But isn’t Eskom installing those ripple switches for this? {Yeah, but until then…. best we do our bit to make our lives easier!}
If you do want to save money try these steps (in the order listed):
*) turn down the temperature setting on your thermostat (mine is set to 35oC) – 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 little or no cold water for your shower.
*) 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.
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!]
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)
*) Lastly, 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.
Detailed explanations:
*) Electricity is used by a geyser each time the temperature of the water goes below the thermostat’s trigger temperature.
*) Refer to the worksheet ‘GeyserThermostat’ for the following explanations:
*) Assuming the water in the geyser is cold to start with, and the thermostat is set at 60oC, then the thermostat will turn on and allow electricity to flow to the geyser’s element which heats up the water [this costs about R2.30 per hour]. After about 65 minutes, the water temperature will be above 60oC and the thermostat will turn off and no electricity will be used.
*) When someone in the household decides to take a shower, the hot water exits the geyser and cold water replaces this hot water which forces the temperature to below the thermostat’s trigger temperature of 60oC. At this point, electricity will again be used to heat up the water to 60oC at which point the thermostat turns off again.
So, as more hot water is used, more electricity is used.
*) 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”
*) 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.
An alternative would be to purchase surge protectors for your most expensive/vital appliances.

Update on 16June2010:
Watch out or, at least, be aware: #WTF Geyser's element has just blown <3 years after installation... 5 year geyser warranty, but only 3 months on the element! #FFS #RipOff


  1. Do you know it is against the adsense rules to encourage people to click on your sponsors. Please remove it or maybe you will be reported!

    Good articel though. Laws of nature dictates that you cannot save by switching geyser off. It is a pitty that the engineering work in this country is now being done by every snotkop that has a PC and can publish shit on the internet. Your article one of the best so far. The engineering fraternaty is laughing at the whole debacle. Forget the geyser for energy saving. Just switch it off to assist Eskom in Peak Load Management.

  2. Hi Anonymous (or is that Tobie?)

    Thanks for your advice re Adsense! I have removed the "words of encouragement" to click on my supporters' ads!

    Thanks too for your kind comment about the article being "one of the best so far" and agreeing that turning off the geyser will only assist to reduce the peak load (that's for a 'non-solar geyser' of course).
    If you have a solar geyser, then it definitely pays to install a timeswitch (as mentioned here: If you have a solar geyser, then make sure you install a timeswitch!).

    I have set my (solar) geyser's thermostat to 35 degrees which is the temperature of the water on cold/cloudy days, but on sunny days the water temperature is much hotter due to the solar panel doing its job.

    Thanks too for your warning on Legionnaires disease. I found references to this on the Internet: "storing hot water at temperatures of less than 55°C is not advisable due to potential for Legionnaires disease"!

    But another article says that the risk is low:
    Heating and water

    "Occasionally one is warned that a cooler tank could develop Legionnaires disease. Personally I believe this to be a very low risk given the high turnover of water in a domestic system. To the very best of my knowledge, Legionnaires disease has never developed in a solar hot water system which typically has a tank temperature between 40 and 50 degrees C."

    Another point, "thermostats are particularly inaccurate, so the best strategy is probably to turn it down little by little until it gets too cool."

  3. OK thanks for this excellent advice - so it seems that a solar geyser with a timeswitch is the way to go... anyone had any good/bad service from the installation companies in Cape Town?
    I'm considering using but I have heard that their after sales service is poor.

  4. @Anonymous 03June:
    I've had very poor service from
    I've been waiting for them to fix a leak in my roof for months now! Every time it rains I have water dripping through my ceiling which is now also damaged.
    So, I'm not a happy customer and would not recommend them to any of my my enemies!

  5. I see that the web site is misleading in that the SABS logo is incorrect and they are not a member of SESSA (Sustainable Energy Society of Southern Africa)
    See list of members here:

    {The web site states: "Member Solar Energy Society of Southern Africa your Protection"
    and has an incorrect SABS logo}

    Howz that for misleading information???!!!

  6. This comment has been removed by the author.

  7. Thanks anonymous - you inspired an article on their false advertising - have you seen it here:

    But, I see that SolarQuip is still (false) advertising - using the SESSA logo - in at least one local suburban magazine {called Home Focus Nov/Dec 2009, page 22} :(

    I looked through the listed members here:

  8. Very Excellent article about saving geyser electricity. You are blog is very informative blog....


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