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Thread: How to size and plan the recirculation circuit?

  1. #1
    DIY Junior Member bandrewfox's Avatar
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    Default How to size and plan the recirculation circuit?

    I have just finished with my PEX supply lines to all the bathrooms and kitchen, and now I am ready to install the recirculation line.

    I have a 2 story house with my HWH in the basement, a powder room and kitchen on the first floor and bathrooms upstairs. They each have a separate pex line, as shown approx in the are in the attached diagram. The blue arrows are my guesses as to where the hot water would come from if I use any of those fixtures (when just the pump is running, then those arrows are obviously not accurate).

    Name:  recirc-plan.jpg
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    My confusion now is that if I install the recirc line as drawn, then it seems like, for example, the kitchen sink would pull in water from any of the tubes? Is that a problem? Is 1/2" the right size? As an alternative, would it be better to have each distant fixture have its own recirculation line, then converge them all at the pump - each with a separate check valve?

    Thanks.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The water will take the path of least resistance. I don't think it will work well the way you have it currently setup.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member bandrewfox's Avatar
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    That's a good point - I guess when the pump goes it will not even pull water in from the farthest fixture (powder room), it will just get water from the closest fixture and biggest pipe (master) and then not anything else? So, then what do I do? If I run 3 separate lines to each fixture and then combine them would that take care of it - how do I ensure that a single pump would pull water from all of those fixtures equally?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on where your manifold is, you might just run the return from it back to the tank. THen, all of the fixtures will be hot, at least from the manifold. Otherwise, you may need to install valves in each return line to get them balanced. Variations in height, number of turns, distance, will all affect where and how it works. Some systems utilize a thermostatic valve at the fixture that closes when the supply water reaches the setpoint. THen, eventually each one in turn would likely get some flow, but it wouldn't work with all of them at the same time.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Your problem is that you should have asked FIRST, before installing the piping. To do what you want to, you should have run the hot water to the powder room, then the sink, and finally to the upstairs bath AND THEN returned the line to water heater. That way ALL the sinks would have "instantaneous" hot water without the hassle and inaccuracies of multiple check and balancing valves. When, and if, you get it working, install a valve between the pump and the water heater, (NOT between the sinks and the pump), then "throttle" it down until it just maintains the temperature in the system.
    Licensed residential and commercial plumber

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    DIY Junior Member bandrewfox's Avatar
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    I did think a about doing it that way beforehand, except then I would have needed much bigger pex. I actually simplified the drawing quite a bit - I have 3 bathrooms on the 2nd floor and a laundry room, so to get enough water to run everything at once, then I would have needed 1" pipe to the powder room and back to the kitchen which seemed like too much of a pain and too expensive.

    But, you gave me an idea, the bathrooms are above the powder room, so I could connect a 1/2" line from the 3/4" line of the bathroom down to the powder room so that the original pipe I used to get hot water TO the powder room would now be the recirc line coming FROM the bathrooms and powder room. Then I only need to deal with balancing 2 returing recirc lines (1= bathroom/powder, 2= kitchen).

    Thanks.

    Any other ideas out there?

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Either tie the kitche into the line between the bath and powder room, or into the line from the powder room back to the heater. You have no idea how vexing it can be to balance even two lines, along with two check valves, and keep them working. AND when one "malfunctions", figuring out the problem can also be taxing.
    Licensed residential and commercial plumber

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