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Thread: single element water heater.

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    DIY Member brother's Avatar
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    Default single element water heater.

    Was changing the heating element on a water heater , and i notice it was just a SINGLE heating element. Im use to seeing a 2 element water heaters.

    Are single element w/h less efficient than 2 element?? Is it easy to just put in another element for the water heater because it has a spot for another element.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Via the high quality of content here in this forum, I recently learned the elements in a dual-element water heater are never on at the same time. The top one is controlled by a switch that disconnects the bottom one during energization. So then, having a second element would not make your heater more powerful. Rather, it would seem to me that a second element would only be most necessary inside a tall tank where the upper element could get things started and then pass the job along to the lower element that would finish warming the water in the tank and take care of smaller amounts of cold recovery water that never make it to the top. Overall, I suspect a second element in a smaller tank would seldom come on at all and mostly act only as a backup in the case of failure of the first element if the upper switch will still let it come on.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    As I understand it, the lower element normally runs as required to keep the entire tank at its set temperature. The upper element comes on only during periods of high demand -- a last-ditch effort to get the outgoing water hot.

    I have a single-element 80-gallon WH as part of a solar system; thankfully, it rarely comes on.

    I don't see why you couldn't add a 2nd element if you wanted to, but I'm not sure how it would be wired. WHs are normally wired assuming only one element will be on at once. There's probably a control box required to make sure they both don't run, or, more likely, there's circuitry in the upper element that controls the lower one.
    Last edited by Mikey; 01-03-2008 at 06:22 AM.

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    Plumber jimbo's Avatar
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    Mikey...How do you plan to add a second element? Just drill a hole and glue it in?? Not to mention, to get a little techincal, any modification of the thermostat set up and wiring violates the UL listing of the equipment, and is therefor a prima facie code violation.


    Was it mentioned how many gallon this WH is? I suspect a smaller one.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I'm not going to add a second element, but the OP implied he was interested in doing so, and said there was a place for one in his tank, so he shouldn't need glue. I agree that this is a job not to be undertaken lightly, and perhaps not at all.

    Do I have this right? What prevents both elements from running at the same time? I can't find my water heater bible just now...

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    In the Trades Bob NH's Avatar
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    Quote Originally Posted by Mikey View Post
    I'm not going to add a second element, but the OP implied he was interested in doing so, and said there was a place for one in his tank, so he shouldn't need glue. I agree that this is a job not to be undertaken lightly, and perhaps not at all.

    Do I have this right? What prevents both elements from running at the same time? I can't find my water heater bible just now...
    The upper thermostat is a control that applies power to the upper element if it is demanding heat, or switches power to the lower thermostat. The lower thermostat then applies power when demanded. The upper thermostat has priority and the lower thermostat can never apply power when the upper thermostat is on.

    If someone wired it up so that both would operate at the same time then the breaker would trip pretty quickly as it would be drawing about 37 Amps.

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    DIY Senior Member Mike Swearingen's Avatar
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    brother,
    Are you saying that you have a two-element water heater that only has a single element in it?

  8. #8
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Quote Originally Posted by Bob NH View Post
    The upper thermostat is a control that applies power to the upper element if it is demanding heat, or switches power to the lower thermostat.
    That's what I thought; thanks.

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    Moderator & Master Plumber hj's Avatar
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    Default Heater

    Some single element heaters have a second boss on them, but it is a closed one so an element will not/cannot go into it. True single element heaters do not have the second cover or element boss. if yours does then it could be converted to a double element heater, but it might be difficult and costly.

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    DIY Member brother's Avatar
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    Quote Originally Posted by Mike Swearingen View Post
    brother,
    Are you saying that you have a two-element water heater that only has a single element in it?


    I think thats I have. Like i said, i have changed elements before and i have a good idea how they work/wired, (where one comes on at a time). I just looks like they just decided not to install the second element. as it has a spot at the bottom to put on in. just unscrew the plug and screw the other element in and wire it correctly.

    But i was just curious as to the advantage, maybe it will give me longer hot water time when long showers(high demand) are going on

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    In the Trades Bob NH's Avatar
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    Quote Originally Posted by brother View Post
    But i was just curious as to the advantage, maybe it will give me longer hot water time when long showers(high demand) are going on
    There are two elements so that the top one, which has priority, can heat the water that is nearest the outlet if it is colder than the set temperature; and if the top one is hot enough the bottom one can heat the new colder water that has just come in.

    In a very small heater they usually install only one element because the inlet and outlet are close together.

    Since only one element works at a time the second element doesn't affect the total recovery rate.

  12. #12
    DIY Member brother's Avatar
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    Quote Originally Posted by Bob NH View Post
    There are two elements so that the top one, which has priority, can heat the water that is nearest the outlet if it is colder than the set temperature; and if the top one is hot enough the bottom one can heat the new colder water that has just come in.

    In a very small heater they usually install only one element because the inlet and outlet are close together.

    Since only one element works at a time the second element doesn't affect the total recovery rate.


    Ok so the recovery rate wont be quicker. by the way this is a 50 gallon water heater.

  13. #13
    Moderator & Master Plumber hj's Avatar
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    Default element

    Single element water heaters, other than solar models, ALWAYS have the element at the bottom, because only the water above the element really gets hot.

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    DIY Member brother's Avatar
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    Quote Originally Posted by hj View Post
    Single element water heaters, other than solar models, ALWAYS have the element at the bottom, because only the water above the element really gets hot.

    Well this particular one has it at the TOP and its a single element heater.

  15. #15
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by hj View Post
    ... only the water above the element really gets hot.
    Quote Originally Posted by brother View Post
    ... this particular one has it at the TOP ...
    I began wondering about all of that last night ...

    The water at the bottom would at least get warm in your heater as it is, but how difficult would it be to move your element to the bottom? Or, is your temperature sensor possibly already below the element? Logic suggests your element should be lower to yield a greater volume of hot water per cycle, but cars all do about the same even though not all of them have the powered wheels at the same end.

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