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Thread: Dual water heaters with recirculating pump

  1. #1

    Default Dual water heaters with recirculating pump

    I am interested in installing a Grundfos UP15-10SU7P/TLC recirculating pump on a dual water heater setup. The tanks are presently installed in parallel with the two outlet lines rising overhead to tie in to the horizontal line. I am unsure where the Grundfos pump should be installed on this particular setup. Should I change the setup so that both tanks merge into one vertical rising pipe and install the pump on that single pipe or should I install the pump "downstream" from both tanks to circulate the water away from the tanks toward the far end of the house to the bathrooms where the transfer/comfort valve is located?
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  2. #2
    Illinois Licensed Plumber SewerRatz's Avatar
    Join Date
    Nov 2008
    Chicago, IL


    Your parallel installation is wrong. The heater on the left is doing all the work. The piping that enters each heater must be exact in every fitting and length, as well as the hot water piping. Both must be exactly the same in length and fittings. If one pie is longer on one heater verses the other the water will take the shorter pipe (path of least resistance).

    Here is a good PDF showing the proper way to plumb in duel heaters in parallel with a return line. http://www.hotwater.com/lit/wiring/315268-000.pdf

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