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    WallyHelps's Avatar
    WallyHelps Posts: 1,018, Reputation: 136
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    #1

    Dec 24, 2021, 11:18 AM
    New water heater and gravity recirc
    I'm replacing my 27-year-old water heater (finally) and want to maintain the function of my gravity-fed recirculation system.
    The heater is in the basement, and the crossover loop is in a 2nd floor bathroom.

    I understand that WHs now have heat traps installed, and that these will prevent my recirc from working. Can I pull the valve out of the traps? Hot/cold/both? Or do I replace them with dielectric nipples?
    A professional plumber will be doing the work. Will he balk at modifications to the new heater? Code problems?

    The WH will be a 75-gal AO Smith gas unit.

    Thanks for any advice!
    WallyH
    jlisenbe's Avatar
    jlisenbe Posts: 4,350, Reputation: 156
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    #2

    Dec 25, 2021, 11:22 AM
    I’d run it by him first. I’m sure he’s run into this before. He’s not likely to do anything not covered by code. My understanding is that a heat trap is not to be used with recirc systems but he will have the best informed answer to that
    massplumber2008's Avatar
    massplumber2008 Posts: 12,831, Reputation: 1212
    Senior Plumbing Expert
     
    #3

    Dec 29, 2021, 02:55 PM
    Hi all

    Your plumber should remove the heat trap nipples and install new dielectric nipples at a new water heater with gravity recirc. If he/she questions it, it shouldn't be too hard to find a good article about this topic on google.

    Happy Holidays guys!

    Mark
    WallyHelps's Avatar
    WallyHelps Posts: 1,018, Reputation: 136
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    #4

    Dec 30, 2021, 03:42 PM
    Thanks Mark!
    The plumber said that this particular WH didn't have heat traps, but I had to see for myself. While it was awaiting hook-up, I ran a long plastic rod down each of the water connections and there were no flaps/balls/etc. The rod went in almost 2 feet without touching anything (that was the length of the rod).

    I explained to him how my system was set up and he didn't think it could work, but it was (and fortunately still does with the new WH).

    Happy New Year,
    WallyH
    jlisenbe's Avatar
    jlisenbe Posts: 4,350, Reputation: 156
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    #5

    Dec 30, 2021, 04:38 PM
    Mark is a good guy to have around.

    I think the gravity systems only work when the WH is below the level of all of the outlets on that system. Correct?
    massplumber2008's Avatar
    massplumber2008 Posts: 12,831, Reputation: 1212
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    #6

    Dec 31, 2021, 06:24 AM
    Name:  thermosiphon.jpg
Views: 46
Size:  82.8 KB




    Correct!
    jlisenbe's Avatar
    jlisenbe Posts: 4,350, Reputation: 156
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    #7

    Dec 31, 2021, 06:39 AM
    How does it get access to the bottom of the tank? Is that where the drain valve would usually be?
    WallyHelps's Avatar
    WallyHelps Posts: 1,018, Reputation: 136
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    #8

    Dec 31, 2021, 08:54 PM
    My thermosiphon hot-water setup
    I'll take advantage of Mark's diagram to show how my system is arranged.
    My WH is in the basement and the sinks shown are in the 2nd floor master bathroom. It used to take a long time to get warm water all the way up there until I installed my recirc system.

    The key component is this:
    Name:  Grundfos.jpg
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    It is supposed to be used in conjunction with an electric pump, but I found that if my WH is in the basement and there are no heat traps, thermosiphon magic gives me quick hot water throughout much of my house WITHOUT THE PUMP. These are in the $50-ish range. Some say they quit working after a year or two, but mine has been working for 5 years so far. It is essentially a temperature controlled valve that "shorts" the hot and cold supplies together until enough hot water has traveled up the line to the valve, at which time it closes, separating the hot and cold feeds from each other.

    Here is my setup:
    Name:  thermosiphon5.jpg
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    The one downside to this arrangement is that the cold water at the 2 sinks is not really COLD until you run it for a while. This is a small price to pay in my opinion.

    Hope this helps someone!
    WallyH
    massplumber2008's Avatar
    massplumber2008 Posts: 12,831, Reputation: 1212
    Senior Plumbing Expert
     
    #9

    Jan 3, 2022, 04:16 PM
    Yes to you John.

    The grundfos crossover valve Wally posted usually works with a pump but I am familiar enough with them that they can work as he described, but as he said, it does leave cold water warmed.

    Thanks for posting, Wally

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