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  • Grundfos recirc sizing with Tankless heater?

    any guidance on what pump (model # please) to use from Grundfos with takagi tankless 199,000 BTU heater with full return loop

    installation is:
    1/2" return loop (80') (can go 3/4" if needed")
    3/4" cold supply off of 1" feed (80')

    heater spec says recirc pump should be min. 2 gal flow at 15 head and 1/12 min. motor

    total loop with fittings and supply distance is under 400 feet

    timer and line plug with clip on thermostat is preferred but can be added...

    most Grundfos recircs are 1/25 HP motors... looking for guidance from your experience

    have seen this example posted online, but cannot read model # of pump
    this pump has 1-1/4" union flange with 1/2" sweat fittings via 3/4" sweat reducer but there are so many options for flanges, fittings, HP , and head vs flow ratings...

    thx in advance


  • #2
    Re: Grundfos recirc sizing with Tankless heater?

    They changed the number on the pumps when they went to stainless body.But you're in the ballpark.

    Recirc. in 3/4" pipe only.

    We can get the number for you.

    Comment


    • #3
      Re: Grundfos recirc sizing with Tankless heater?

      If that Takagi tankless has a warranty that is anything like the Rinnai tankless warrranty, you are shortening the warranty by using the recirc pump like you have in the picture. You have to have a six gallon electric water heater to recirc with, otherwise that tankless is going to be firing all the time.

      Comment


      • #4
        Re: Grundfos recirc sizing with Tankless heater?

        Originally posted by Nevada plumber View Post
        If that Takagi tankless has a warranty that is anything like the Rinnai tankless warrranty, you are shortening the warranty by using the recirc pump like you have in the picture. You have to have a six gallon electric water heater to recirc with, otherwise that tankless is going to be firing all the time.
        I was thinking the same thing.
        THE GLASS IS ALWAYS HALF FULL

        Comment


        • #5
          Re: Grundfos recirc sizing with Tankless heater?

          Originally posted by Nevada plumber View Post
          If that Takagi tankless has a warranty that is anything like the Rinnai tankless warrranty, you are shortening the warranty by using the recirc pump like you have in the picture. You have to have a six gallon electric water heater to recirc with, otherwise that tankless is going to be firing all the time.
          correct. a tankless with a recirc. pump is going to wear out the heat exchanger pretty quick. a 6 gallon electric to use as your storage / recirc is going to help you with the wear and tear, but it's going to hurt you in the electric dept.

          the 6 gallon with the small pump is fine. su15/18 (union) sf (flange)

          without a tank you need a grundfos sf24/64.

          by the way. the pump and timer araingement you have is not rated for outdoor use. the rain will ruin the the electronics

          rick.
          phoebe it is

          Comment


          • #6
            Re: Grundfos recirc sizing with Tankless heater?

            all good
            thx guys

            the picture is not my project but i agree the weather would impact that timer,etc
            this install is from a plumbers website showing their work

            thanks for the info.

            the recirc pump will be on a timer for 30mins per day or so only, etc to fire off only at 5am so its hot water for morning showers at 5:30am etc

            since tankless does not equal instant hot at the shower unless its next to shower, this makes sense

            not sure we need the extra tank just for this... what do you think?

            thanks for the model #s

            Comment


            • #7
              Re: Grundfos recirc sizing with Tankless heater?

              Originally posted by markk View Post
              all good
              thx guys

              the picture is not my project but i agree the weather would impact that timer,etc
              this install is from a plumbers website showing their work

              thanks for the info.

              the recirc pump will be on a timer for 30mins per day or so only, etc to fire off only at 5am so its hot water for morning showers at 5:30am etc

              since tankless does not equal instant hot at the shower unless its next to shower, this makes sense

              not sure we need the extra tank just for this... what do you think?

              thanks for the model #s
              I would think as long as you stick to that small window of time you will be fine. Although install the appropriate model as Rick suggested.
              THE GLASS IS ALWAYS HALF FULL

              Comment

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