Gravity Recirculation - Cold water runs hot for 30 sec

Discussion in 'Water Heater Forum, Tanks' started by Jeff Homan, Apr 26, 2021.

  1. Jeff Homan

    Jeff Homan New Member

    Apr 26, 2021
    Loveland, CO
    Hello all. I'm looking for some troubleshooting advice on our house we recently moved into. I have a two tank hot water parallel system with gravity fed recirculation loops. The gravity recirculation has two loops that tee together into the drain of one of the tanks. The two loops cover two "sides" of the house. The tee is about 10-15' linear from the drain with no insulation on that section. I do not see any check valves in these loops.

    On the south side of the house with the kitchen and laundry, I have two kitchen type faucets that have single handle blending fixtures plus a powder room and bar with standard two handle faucets and the wash machine feeds. The system functions as expected for hot water. However, when I open a faucet for full cold on the south side, it will run hot for 20-30 seconds. My theory is the gravity feed is pulling the cold through the blending fixtures. Not sure if it matters, but we have a well with a pressure tank.

    I don't seem to have the same issue on the North side even though those bathrooms have two shower faucets with single handle blending type faucets.

    If the blending faucets are the issue, is there some sort of check valve I could install at the faucet connection to prevent the back feed? Or should I install a check on the cold side by the hot water tank. I don't have a horizontal plumbing exposed by the faucets so I may need to plumb a loop in the cabinet if needed. The hot water tanks and a lot of the plumbing is exposed in the basement and crawl space.

  2. Sylvan

    Sylvan Still learning

    Sep 23, 2004
    plumbing - fire suppression - boiler inspector
    New York
    Forget the check valve

    Use a heat sink on the CW supply to the tank, meaning run the CW line 27" down then make a loop and bring the CW line back up to the tank.

    Installing this will prevent the stratification of HW molecules from entering the cold water line
    phog likes this.
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  4. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
  5. Jeff Homan

    Jeff Homan New Member

    Apr 26, 2021
    Loveland, CO
    I do feel my cold line is hot at the tank out to where I can longer access, I will give that a try. Question - what is the 27" based on? 27" lower than than CW inlet?
  6. Tuttles Revenge

    Tuttles Revenge In the Trades

    Oct 15, 2014
    I call what Sylvan describes a heat trap.. Basically heat rises.. it won't follow and heat the water on the downward part of the loop..

    google search for Heat Trap Loop and you will get a bunch of visual references.

    But.. I'm with Reach4, tho i've never installed a gravity system, they were how recircs worked before pumps. I'd install a swing check on a 45°
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