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Thread: Hot water recirculation plumbing

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  1. #1
    DIY Junior Member Markchgo's Avatar
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    Default Hot water recirculation plumbing

    I have a conventional 50 gallon hot water system with a recirculation pump and separate return line which returns to the bottom of the tank at the drain connection; all pretty standard stuff.

    I notice however that when showering, the hot water seems to deplete more quickly when the pump is running. I'm thinking that by circulating the hot water back into the bottom of the tank, then hot and incoming cold water are being mixed and circulated when showering which cools all the water in the tank more quickly.

    It seems to me that it would be better to have the return hot water line enter the tank near the upper portion of the tank, in this case at the pressure relief connection point on the side. This way the hot water all stays at the top of the tank and the incoming cold water enters and stays at the bottom of the tank ready to be heated.

    What do you guys think?

  2. #2
    Moderator & Master Plumber hj's Avatar
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    You know absolutely nothing about a recirculation system, and your diagnosis is faulty. Connecting it to the T&P valve opening would violate EVERY plumbing and Underwriters's codes. More likely is that the check valve, if you have one is broken.
    Licensed residential and commercial plumber

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    While you can run the recirc pump continuously, some systems do that, but have a thermostatically controlled valve that shuts it down when the water is already hot. The unit I have, only runs the pump when the point of use is not warm enough, then it runs (typically less than a minute), then shuts off. It may only runs 3-4x per hour. Lots of on/off cycles, which may be lousy for the pump, but it's lasted now for over 7-years without issues. If you ran the return into the top of the WH, it would potentially end up diluting the hot that's there, since it would cool off after flowing both to the point of use, and all the way back to the WH again. Standard operation is to return it to either the cold line, or the drain location if the tank doesn't have a dedicated recirculation port. FOr a long shower, to extend your hot water for showering, consider a drain water heat recovery system. Do a search, and you'll find lots of discussion on them here in this forum. And, check your recirc's check valve is still working as HJ mentioned.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member Markchgo's Avatar
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    My original configuration had an aquastat to cycle the pump and shutoff valve based on return water temp but I was unable to find a place to put it that adequately monitored the temp up by the faucets. In the winter, the water in the walls cools quickly, while the water in the basement return pipe stays warm so the pump would not cycle frequently enough; I went back to continuous operation with a timer that runs the pump only during peak usage hours. I do have fairly new check valves in each branch and they seem to be working.

    With continuous operation, the water in the entire recirculation loop is hot, so my thinking was to return it to the top of the tank. (my plan was to tee into the T&P connection which would bring the T&P valve outward about 3 inches; seems to me it would still function properly)

    Any further thoughts?
    Thanks

  5. #5
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by Markchgo View Post
    Any further thoughts?
    I think it is a bad idea. The return flow will be cooler than the tank outlet and so will cool the T&P, defeating its intent. Listen to hj, despite his bedside manner. If you think it is a blending problem, my guess is you used too large a recirc pump. Try reducing the flow on the recirc with a dole valve.

    When the recirc is off for any length of time, you are probably experiencing a phenomenon known as temperature stacking which results in water that is hotter than the high limit stratifying at the top of the tank. When there is no hot water use for some time, this stacking effect minimizes as the temp evens out throughout the tank. The recirc pump will not let the stacking occur.

    If you don't have adequate hot water for the shower, you may consider raising the temp a bit as long it doesn't present a scalding risk.

  6. #6
    DIYer, not in the trades LLigetfa's Avatar
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    Here is an explanation of "stacking".
    http://www.customvac.mb.ca/water_heaters_safe_1.htm
    Another especially hazardous condition is known as the "stacking effect," this is more pronounced in gas water heaters due to the aggressive manner in which they heat water. This stacking occurs due to the natural rise of hot water in the tank, kind of like stacking pancakes, each at a different temperature, cooler ones below and the hot ones stacked on top. As an example, a water heater set to maintain 130F without a circulation pump could have water temperatures between 130F at the bottom and 190F at the top, a very hazardous condition.

  7. #7
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by LLigetfa View Post
    ...as long it doesn't present a scalding risk.
    ...or deploy a thermostatic mixing valve.

    http://www.wattscanada.ca/pages/lear...asp?catId=1159

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