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Thread: mini storage tank for dedicated recirculation loop

  1. #1
    DIY Junior Member yoyolandre's Avatar
    Join Date
    Dec 2011
    Boston, MA

    Default mini storage tank for dedicated recirculation loop

    So, I already have a thankless water heater and since I'm in the middle of some heavy-duty remodeling of the house, we are thinking of installing a dedicated hot-water recirculation loop in order to get rid of the cold water sandwich and of the delay. my thinking, is that Navien has the right idea, at least in concept, and I want to emulate it in my home. problem is, I can't find a small buffer tank of say, 3-5 gallons, except for an expansion tank. I think it might do, but I'd like your opinion on the matter.

    here's the layout I was thinking of:

    tankless to expansion, to faucets, to Redytemp pump, to tankless.

    the reason for a 3-5 gallon storage tank is that we have 2 growing kids who can't brush their teeth while one of us takes a shower. to say nothing of running the dishwasher or a load of laundry. a buffer tank would allow the tankless enough time to "catch up" to the spot demands.

    what are your thoughts ?

    Thanks a lot, and happy new year!!!

  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    Do not use an expansion tank as a recirculation buffer. A small "point of use" electric HW heater would do the trick.

    Running a recirculation loop lowers the as-operated efficiency of the system by quite bit though.

  3. #3
    DIY Junior Member yoyolandre's Avatar
    Join Date
    Dec 2011
    Boston, MA

    Default forget efficiency...

    I get it would decrease the efficiency. it's a drawback I'm MORE than happy to hit if it increases the comfort level sufficiently ...

    I think as an alternative to a full-blown recirc loop, I would add the 4 Gal tank at the main outbound for and have it cycle through the recirc temp only on a schedule. something like this:

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    with the stated objective of reducing the cold water sandwich effect when we forget we have a load running in the laundry when my wife is trying to take a shower in the AM.

    we'd have the redytemp run from, say 6:30 to 7:30 morning and evening, for example, and keep the buffer tank nice and toasty during that short window and increase water comfort level.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    If you don't run the recirculation constantly OR power the POU tank, you think your cold water sandwich is bad now, just wait! The tank will cool off (some, it is insulated, though) through the day, and unless in the period when your recirculation is running, potentially be cool and you'd have to dump all of that before you'd get hot water.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Junior Member Surfing Plumber's Avatar
    Join Date
    Sep 2011
    Orange County, CA


    Navien uses the buffer tank as a marketing gimmick... The reason Navien needs a buffer tank because the machines can not bring the temperature up to par as fast as other brands, it will need to constantly recirculate within itself to provide hot water. It is not efficient at all when using with the recirculation system built in.. I have installed many Navien when it first intro in the US, I have not installed any after 15+ call backs from my customers...


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