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Thread: PEX-conventional or mainfold

  1. #1

    Default PEX-conventional or mainfold

    I am currently in the process of building a house and getting ready to start the plumbing. I am using pex with copper fittings at the shut off valves. My plumber who is assisting me wants to plumb the house like a conventional copper system. I have come accrss many houses that have a manifold system with homeruns for all the pex. I want to make sure I get the best possible system with the best pressure everywhere(especially since I have a well which yields about 10-12 gpm) and I am wondering which way is better to plumb the system

  2. #2
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    My non-professional plumber's opinion: Run home runs to a common accessible manifold. Makes it easier to isolate any fixture, reduces the number of joints and fittings in hard-to-reach places, assures constant pressure at all fixtures, and looks impressive. I don't know the numbers, but I'll bet the extra cost of the PEX tubing is offset by reduced labor costs to install.

  3. #3
    That's all folks! Gary Slusser's Avatar
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    Quote Originally Posted by skkipp View Post
    I am using pex with copper fittings at the shut off valves. My plumber who is assisting me wants to plumb the house like a conventional copper system. I want to make sure I get the best possible system with the best pressure everywhere(especially since I have a well which yields about 10-12 gpm) and I am wondering which way is better to plumb the system
    Then run homeruns from a Manabloc (check the spelling) manifold. I see little advantage of branch and tee like copper, homerun has many advantages and few if any disadvantages.

    As to your 10-12 gpm... that is your well recovery rate, not the gpm the system will deliver to the house, and it has absolutely nothing to do with pressure. Pressure is resistance to flow and is controlled by the pressure switch settings that operate the pump and the precharge air pressure psi in the pressure tank.
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
    CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A hybrid solution would be to run larger runs to say a bathroom group, then install a mini manifold for that group (maybe run 3/4 or even 1" then branch off to 1/2" or 3/4" to the individual fixtures). Using home runs does mean the use of a hot water recirulation system is more complex, if you wanted to do that and, after running water at the shower, you'd still have a full run of potentially cooled off water to run to the faucet on the sink. If the hybrid was used, you'd have hot at the local manifold.
    Jim DeBruycker
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    Master Plumber Redwood's Avatar
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    The biggest disadvantage of the homerun system is the inability to run a recirculation loop. In a small home that is not a big deal, but if you have a McMansion and your master bath suite is at the far end of the house over the garage and you run the hot water at the lav for 5 minutes before it shows up, then you go over to the shower and run it for another 5 minutes, then the wife comes in and goes to her lav sink runs it for 5 minutes then steps over to the soaker tub and runs it for 5 minutes you might just want to do something about it!

    Now the kicker! The plumber comes and tells you that you have a homerun system and thats the way it is unless he tears up walls and ceilings to put in a hybrid system with mini-manifolds where recirculation is possible.

    One thing for sure... You will be cursing the idiot that decided to make your water supply a home run system!

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Quote Originally Posted by Redwood View Post
    The biggest disadvantage of the homerun system is the inability to run a recirculation loop.
    Excellent point... and these days I wouldn't build a home without a complete loop. I use a couple of under-sink on-demand pumps at opposite ends of the house now, but they're very noisy. I used to be skeptical about the whole-house loop systems because I felt they wasted a lot of energy keeping the loop hot, but there are pretty good on-demand controllers now, and with my solar system, energy is cheap!

  7. #7
    That's all folks! Gary Slusser's Avatar
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    There's only one reason for not being able to install a recirc system in a manifold PEX system and IMO it is a lack of imagination and desire. And I'm sure that if desired to imagine for a few minutes I could find a way. Like running a loop from each hot water fixture back to a manifold on the water heater drain at the bottom of the tank, like a lot of branch and tee copper systems do it. And to cut down on tubing, do a small manifold in each bathroom after tying the hot fixtures together and run line back to the heater from each bathroom. Of course that would have to be done in new construction and the same goes for branch and tee copper.

    Also, life is a trade off one thing with advantages compared to its disadvantages. A branch and tee system has many more disadvantages than a manifold PEX system.
    Gary Slusser Retired (= out of business)
    Click Here to learn how to correctly size or program a water softener.
    CAUTION, as of Nov 12 2013 all YouTube videos showing how to rebuild a Clack valve have an error in them that can cause damage.

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