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Recirc pump on hot outlet of indirect ?

yesterday . The Grundfos circ with the timer was piped right into the hot out of the tank , pumping away from it . I looked around the mechanical room for a recirculation pipe . Didn't see any .

We reconeccted it the same way on the new tank . It seemed to work , but very slowly .

Could this setup be working on one pipe ? Or does it absolutely need a recirc line connected to the cold piping somewhere ?


  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    Grundfos comfort pump systems were designed to work that way. Under one or more fixtures you should find a plastic thermostatic bypass manifold piped in the supply lines.
  • billtwocase
    billtwocase Member Posts: 2,385
    re-circ line

    Ron, you get all the good ones lol. For it to work, should have been Tee'd into the cold supply with a check valve. Is there a hot water supply loop somewhere in the basement? peace
  • Yep

    We tried this setup once , with the circ situated under the kitchen sink . Had to take it out because everytime the customer opened up the cold side of the faucet they'd get a 2 second blast of hot water ......... It was also happening in the toilet adjacent to the kitchen .

    But , piped the way you see it in these pics , won't the whole cold pipe from the plastic manifold back to the heater get filled with hot water ? The customer had no complaints though .
  • Hey Bill

    Yes we do get the good ones , lol . Here's a better pic of the boiler . Of course they didn't leave enough room to squeeze the indirect through . We had to clean and jerk it up onto the blocks surrounding the 2 oil tanks . And that tank gets HEAVY ......

    I didn't see any recirc line around . I was feeling for the cold pipes in the mech room to get hot . Didn't happen . I was wondering if this pump was somehow pushing hot water up and back through one single pipe ? That can't be , can it ?
  • billtwocase
    billtwocase Member Posts: 2,385

    Gotta love them stone lined tanks Ron. Heavy, but don't last. That pump will do nothing unless it can return back to the heater, or has a loop where water can move, and not only when a faucet is opened. If there is a hot water pipe coming back from the furthest hot water fixture, back to the tank, that's the one that shoud connect to the cold inlet at the tank with a tee. If there isn't a long run to the fixtures from the tank, scrap the re-circ. Water might be cheaper than electric in that case. Peace
  • Home Depot Employee
    Home Depot Employee Member Posts: 329

    Bill, I don't think you understand how the retrofit grundfos comfort system works without the return line.

    Not my favorite choice but plenty of applications

  • Checked out the link

    The instructions say to mount it on the discharge side . But the animated movie on the site shows it on the cold inlet .

    I read the FAQ . Did not see the question of hot water crossing over to cold side of faucets .
This discussion has been closed.