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Saving Electricity With Your Geyser.

  1. Aug 21, 2011 #1
    We're told that by switching off your geyser when you're not using it, like during the day when you're at work, saves electricity, but is this correct?

    When you keep switching your geyser on and off it has to keep heating up cold water, but when you have it on all the time it maintains it at some temperature. Doesn't it take more electricity to heat up cold water that it takes to maintain some temperature, in the same way it takes more energy to accelerate to some speed than to maintain that speed?

    So does turning your geyser off during the day actually save water or not?

    Wouldn't the better thing be to set your geyser to heat the water to a slightly lower temperature?
  2. jcsd
  3. Aug 21, 2011 #2
    It doesn't save water, no. It does save electricity. In fact, it is less efficient to maintain the water at a high temperature, because your heat losses will be greater.

    It might depend on the heater (I believe geyser is a word for hot water heater), but from a "pure physics" standpoint you will lose more energy maintaining the temperature than in the heating process.
  4. Aug 21, 2011 #3
    All right, I said 'save electricity' twice and 'save water' once, obviously a mistake.

    Anyway, most geysers ('water heater' if you like) have some sort of padding or whatever to help them maintain their temperature. In fact, I should think all new houses will come with padded geysers, and it's only the old ones where people haven't added the padding that lack it.
  5. Aug 21, 2011 #4
    I wasn't trying to poke fun at you or anything. I was just making sure it was clear.

    Think of it this way: even with the insulation, you are still going to lose some heat from the water to the surrounding air. If you keep it at room temperature until you need it, you won't be losing that heat while it's at room temperature.
  6. Aug 21, 2011 #5
    iirc, heat loss through the wall of the tank and insulation will be approximately proportional to the absolute temperature difference between the water and ambient temp outside the unit. which is why KN is saying the loss is greater if you maintain a higher temp.

    also, if you keep a home air-conditioned, then every heat source in the home is more heat that the heat pump has to pump out. so there may be an additional energy loss there.
  7. Aug 21, 2011 #6


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    Analogy time!

    It's like setting your car on a treadmill for 10 hours while you are at work.
    Does it take more energy to get up to speed than staying at a constant speed? Yes!
    Do you put your car on a treadmill whilst at work? No!
    Is that what we are effectively doing by leaving the geyser on all day? Yes!
    So why don't we turn off our geyser? Because you'd forget to turn them back on! And you'd be stuck taking a cold shower in the morning, as you are late for either work or class, and don't have time to wait for the geyser to heat up the water.
    No. But I think someone beat me to this answer.
    That's what I did. I can take a shower with my faucet set on the full hot, and not get scalded.

    ps. Pardon our confusion, but American geysers look like the following:


    and not like the following:


    But it's interesting that our geyser and your geyser's purpose seem to be somewhat related:

    I did not know that.
  8. Aug 21, 2011 #7


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    OMG, I read so much of this looking for the common method by which a geyser could be shut off. Hah ha, thanks all for a little cognitive dissonance there.
  9. Aug 21, 2011 #8


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    And the British "geyser" is pronounced the same way as the American "geezer" which leads to jokes about American tourists in the UK being taken aback when they check into a cheap hotel and are told to "watch out for the old geezer in the bathroom."
  10. Aug 21, 2011 #9


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    Great visuals but I still have no idea what a non-American geyser is. Presumably something to do with household water?
  11. Aug 21, 2011 #10


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    It's a small wall-mounted water heater for a single room, usually the bathroom.


    I first saw one when I visited a cousin in Germany almost forty years ago.
  12. Aug 21, 2011 #11


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    The visuals were hyperlinked, just in case someone got confused, as I was at first.

    Some of those hot water heaters do look like R2D2.
  13. Aug 21, 2011 #12


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    Wait! What!? So they are not the equivalent of American hot water heaters?


    That is weird though. The first time I saw such a thing was 41 years ago, when I was visiting my German cousins. Your cousins didn't live in http://en.wikipedia.org/wiki/Bad_Oeynhausen" [Broken] did they? That would be doubly weird.

    Last edited by a moderator: May 5, 2017
  14. Aug 22, 2011 #13
    A geyser, pronounced "geezer", is a water-heater, not necesarily a small one for one room.
    A geyser, pronounced "gayzer" or "guyzer", is a hole in the ground that shoots out hot water, like in OmCheeto's picture.

    Anyway, thanks for clearing it up. I was just wondering about the physics, because different people tell you different things. The government says switch off your geysers, and "experts" on the radio say don't bother. I was thinking about it as I was driving home late at night, and I thought I still had to switch on the geyser, which made me angry.
    Last edited: Aug 22, 2011
  15. Aug 22, 2011 #14


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    I'd have to see that government statement to see exactly what they were talking about, but yes, shutting it off when not in use will save energy-- just not enough to bother with unless you go away for a few days. Water heaters are thermodynamically 100% efficient so there is no "acceleration" penalty.
  16. Aug 22, 2011 #15


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    I can see the big water heaters (or geysers), but I don't get how turning off your point-of-use would make any difference (short of the current for electronics / natural gas for pilot light, assuming no tank). Anybody know / have a study for how much more efficient point-of-use for hot water is, as opposed to central hot water? Probably too many variables for a good study on that one.
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