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PEX manifolds

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  • PEX manifolds

    i see these manifolds occasionally used with PEX piping and I wonder what the logic is behind it other than having all control valves in one location. However if you need to penetrate structural members you might have to make multiple holes to run the pipe out to the plumbing fixtures. Moreover you might have numerous pipes taking up space that could accommodate ducts or electrical runs. With the added weight, additional fasteners, noise what do you gain by installing these manifolds?

    it seems that useing a standard layout would make more sense since you reduce the amount of penetrations, open up space that might be taken up but multiple pipes and you wouldn't have to mess around with a manifold.

    ive got a buddy that's going to build a house and wants to use PEX, are these manifolds a neat trick or is there more to it?
    PEX manifold

  • #2
    I have 3/4" Wisbro-Pex and a copper 3/4" manifold system....The best ever!
    I ran 3/4" Wisbro-Pex to all fixtures then stubbed out with 1/2" copper with shut off valves too..

    With the manifold system fixture service eliminates losing water throughout the entire house.
    Also, now when taking a shower and someone flushes the toilet I do not lose pressure or scream
    when the cold supply changes.

    This method also ensures an uninterrupted run to each fixture and no connections that
    could leak in the future.

    My opinion is to go for it you will never regret it..also use quality ball valves!

    Cactus Man


    • Mightyservant
      Mightyservant commented
      Editing a comment
      Thanks for the input!

  • #3
    Both types will work fine. Seems I recall some of the "composite" (plastic) manifolds fracturing and requiring repair prematurely?

    The advantage of the manifold is having a plumbing circuit panel kind of like an electrical panel. Control of each individual fixture remotely. That can be a big plus in the long run if you ever need that kind of isolation/control. And running the extra pipe involved does not take up that much of space in my opinion if that's how they want to go.

    As stated previously, use quality ball valves. The one's in the picture, if they are similar to ones I've encountered (look similar) can become problematic in only a few years. Stiff and higher potential for leakage and/or breakage.

    I can't agree on a big balance advantage though. A traditional system can be installed where there isn't much, if any, temperature shocks or real imbalances. And all shower valves that are legal to install will be pressure balanced anyway.

    The disadvantage to a manifold system is that you will have to use a lot more pipe and labor for installation.

    Example: If you have a bathroom with two sinks, a tub shower, and a toilet that's 50' away from your manifold then you'll be running roughly 240' of cold line and 180' of hot line just for this one bathroom. (Estimating conservatively 60' runs for the ups, downs, curves, etc.)

    Whereas with a traditional install you could have a 50'-3/4" hot line and a 50'-3/4" cold line running to the bathrooms. Plus an estimated 40'-1/2" hot & 40'-1/2" cold depending on layout.

    Manifold: Roughly 420' of pipe, hangers, labor, and the manifold.
    Traditional: Roughly 180' of pipe & hangers.

    I'm sure you can do the multiples from there.

    The disadvantage of the traditional system though is that you will not have that remote isolation and control however. But that's about it.


    • Mightyservant
      Mightyservant commented
      Editing a comment
      So your running a series of loops to each fixture or zone? I think it's cool to be able to shut a zone or fixture but you'll still have trapped water. Not really sure conveiniance would be enough to sell me on the manifold but If it's needed then it's needed. For me it's easier to shut the main source and your done, no other valves to worry about.

      Thanks for your input!
      Last edited by Mightyservant; 01-12-2018, 10:48 PM.

  • #4
    another advantage is on the hot, you really don't need a return line as all you're wasting is the small quantity of hot water in a 1/2'' pex line. not a bunch of water in 3/4'' or 1'' line.

    yes, it acts as a circuit breaker when needed for future maintenance. All home runs and next to 0 joints in the wall.

    phoebe it is


    • #5
      The following are my assumptions and not meant as pro or con, I'm just trying to understand how it works.

      1. Your installing double the pipe, therefore

      2. Double the penetrations

      3. Double the fasteners

      4. Double the sound caulk, fire caulk

      5. Double the weight of water on the structure.

      However you end up with improved hydraulics, centralized control valves, are able to shut down specific fixtures without interrupting service to the rest of the house. It makes sense if you end up with a superior system that delivers performance that's distinctive. Admittedly in some massive houses that are more like buildings, it would be nice to be able to shut down a specific fixture.

      For the sake of discussion, would not a simple loop for cold and another loop for hot deliver more or less the same improvement in water flow? You would reduce your installation costs since it's a much simpler layout however you would not have the benefit of centralized control valves which on some enormous houses may not work to well. Thoughts?


      • #6
        I would think you could reduce pipe by putting a manifold on each level of the house for fixtures on that level. A stairway closet could easily be used for the upper floors. Then you have only one main run to each level. Yes it puts a singular line to fail that could knock out service to the second/third level, but still gives you the advantages of zones/isolated fixtures


        • Mightyservant
          Mightyservant commented
          Editing a comment
          10-4, that would be an idea worth looking into on some larger homes, I feel that with your sources properly sized the uses of PEX can be reduced and still get the performance. Hot water might require a little more planning so your not wasting or waiting for warm water which is a problem in CA. thanks for the input.

      • #7
        Rick- "Another advantage is on the hot, you really don't need a return line as all you're wasting is the small quantity of hot water in a 1/2'' pex line. not a bunch of water in 3/4'' or 1'' line."

        I'm not so sure about this. Yes, smaller pipe, less volume, less time. But remember this as well. That just gets it there for ONE fixture outlet. So you empty that 60' line at the sink to get hot water there, but you have to do it again for the shower. You have to do it again for the tub. Etc.

        A traditional system gets the hot water to the area to be available closer and quicker by ALL fixtures.

        Just seems it's a non-factor really. Guess it depends on layout, design, and needs.

        Mightyservant- You won't necessarily have twice the penetrations. That will depend on layout of the structure. 6 cold lines could be stacked and ran along a floorjoist along with 5 hot lines on the other side without penetrations for first floor. Going to the second floor could require more though. I can't say it would add up to be double though.

        You probably would have double or MORE of fasteners and pipe. But a few less fittings.

        Double the caulk? Maybe. Again, depends on layout and design.

        Double the weight of water? Probably. But I would think that would be negligible to the structure really.

        I wouldn't think or let any of the things you list as possible detractors keep me from installing a manifold system if that's what I wanted. Just be aware of them, which I think you are.

        And as stated earlier, there is no real hydraulic balance benefit with a manifold vs. a properly sized & designed traditional system. I rarely go in a house where people are so dissatisfied with performance saying, "We wish we would have put in a manifold type system...." As a matter of fact, I have NEVER ran into anyone that has said that.

        Your loop of cold and hot proposal should work just fine.
        A manifold system will work fine. It just gives you isolation of each fixture from a remote location. That's about it.


        • #8
          You also can run 3/8 to fixtures other than showers. Less loss on the hot side.


          • #9
            Originally posted by rjniles View Post
            You also can run 3/8 to fixtures other than showers. Less loss on the hot side.
            That's true and may gain the real efficiency. Think I've only ran into it one time from someone else's install. Wonder why it's not done more? Long distance friction loss?


            • Mightyservant
              Mightyservant commented
              Editing a comment
              I would think depends on the method, 3/8 is getting tight enough where noise could be a factor, but then again the angle stops and hoses going to the fixtures probably are going to help.
              Last edited by Mightyservant; 01-13-2018, 09:40 PM.

          • #10
            Sound like the best setup would be individual runs per room/area. Less runs than a line to each fixture. If you really wanted to, mains run into the vanity and could have a manifolds here for each fixture in the room that would allow easy shut off of a shower or tub.


            • #11
              Thank you all for your advice, a lot clearly depends on the type of system that is best suited to the house and the arrangement of the structural members as well as what your customer wants.

              i would think that if a installer would use PEX in a conventional layout you could maximize the benefits of using that system in a standard manner so it's performance is more or less predictable, you save labor with fewer fasteners, drilling, sound and fire caulking and save on material.

              If you prefer the control valves to be located in one area you could still do that in a conventional layout and if you needed to improve the flow you could loop it back to the source.

              Youve all been a big help, thanks again


              • #12
                Of course you could incorporate a pex system that uses domestic water and loops through the fire sprinkler system. That way it's all domestic and not stagnant sprinkler water.

                I might be able to recommend a sprinkler guy

                phoebe it is


                • Mightyservant
                  Mightyservant commented
                  Editing a comment
                  If I remember right you need to submit your design for both the sprinklers and the the domestic water systems and your less flexible on changes at least here, if there are big changes you'll have to resubmit revised drawings and calculations. I don't think it's a good idea to combine the two. If you break a head the smell will be the least of your worries.

                  CPVC or copper isn't so much a problem with stagnating water, even galvanized pipe stays pretty clean. My favorite is black pipe, I've trashed many Carhart bibs and Duluth long tail tees working with sprinklers piped with black steel oh the humanity, smells like money tho .
                  Last edited by Mightyservant; 01-13-2018, 11:16 PM.