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Thread: Electric flip-flop hot water tank

  1. #1
    DIY Junior Member Bobbyl00's Avatar
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    Question Electric flip-flop hot water tank

    Two people living in house. Disconnected lower heater and sufficient hot water available. Reconnect lower heater when all family visit and there are some sleep overs. I respect the dangers of electricity and turn off power during change over. I'm only heating the upper half or so of the water tank. Question is do I save anything on my energy bill? (40 gal tank)

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    There will be convection in the tank, so I don't think you're actually saving any money.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member Bobbyl00's Avatar
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    If there is convection in tank it would only occur from the top heater level (and only when it is on) since the hot water rises and the water feed is at the bottom , cold and heavier than the hot.

  4. #4
    Nuclear Engineer nukeman's Avatar
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    Nope. You won't save anything (at least nothing that is noticeable). You are still using 'X' number of gallons of hot water per month and it takes a fixed amount of energy to heat the incoming cold water to the storage temperature. Even if you are just using the upper element, you are still really heating the whole tank. Heat moves from hot to cold, so that hot water that is sitting on the top is going to cool down while transferring energy to the cold water on the bottom. So when nothing is being drawn from the tank, the top element will continue to cycle ON to heat up this upper layer of fluid until the entire tank is hot. In addition, even if you are thinking that doing this will reduce standby losses by lowering the average tank temperature, you have to remember that electric tanks are very well insulated and the cost of storing the hot water (at normal temps) might be $20 or so per YEAR. So even if you saved anything by doing this, you might save $5/year or less.

    Better options:

    - turn down the temperature on the tank (if greater than 130*F)
    - insulate the hot water lines that you have access to (get 3/4" foam, not the cheap 3/8" stuff).
    - use less hot water (turn down the temp in the shower, use a lower flow shower head, take shorter showers, etc.)
    - a recirculation system or point-of-use small tank heater may save some money is you have some long runs from the water heater where you constantly have to run the hot for an extended period before the hot water reaches the tap
    - could add a blanket to the WH, but it is not needed in most cases (especially if it is a newer WH)
    - add a solar setup to pre-heat the water (may or may not be cost effective)
    - look into drain water heat recovery (http://www.energysavers.gov/your_hom.../mytopic=13040)..several posts on here (terrylove.com) by memeber "Dana" on the subject

    Basically, you are best off using less water that needs to be heated than trying to reduce standby losses.

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