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  1. #1
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    Repipe- manifold vs trunk/branch

    My question for the group pertains to repiping the water supply hot and cold lines within our house. Should we use manifold home run or trunk and branch pipe configuration?

    Here are more details:
    We have polybutylene water supply pipes in our 1997 home. Polybutylene pipes represent a risk for spontaneous leak and rupture. Should this assertion cause controversy I’d like to avoid a polybutylene discussion. We are choosing to repipe rather than wait and see. Currently I am in the middle of refinishing the basement after foundation water intrusion remediation (separate issue). Because of exposure, I am considering repiping the basement and first floor with PEX so that the plumbing inspection for the current permit will cover the minor bathroom work and the repipe. We’d repipe the second floor maybe in a year or so.

    I am favoring a PEX manifold in the basement utility room, something like the Viega Manabloc https://www.viega.us/en/products/Cat...-manifold.html feeding individual “home-run” lines to all fixtures (1/2 or 3/8 depending on fixture). I believe that every line could be run between the manifold and fixture without any intervening fitting, owing to the space offered by truss floor design. We have need for about about 19 cold and 12 hot lines, so a 36 manabloc would suffice.
    The other option would be to repipe with trunk and branch. Many more fittings, tees, etc, but less line pulling and less space in the utility room.

    As an aside, copper is fine, I have done it, but I’ll be running pex.
    .
    Does anyone have an informed opinion about the general situation or the specific manifold/home runs vs trunk-branch choice?

    thanks
    Last edited by redknife; 07-09-2018 at 11:48 PM.

  2. #2
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    Re: Repipe- manifold vs trunk/branch

    About the only real argument against a distribution manifold is the added cost of all the extra line you will be running, otherwise it has the advantage of more stable water pressure than a shared main line (especially if that main line run is undersized).

    You will likely want to do a little research on the PEX side as there are several competing PEX systems/manufacturers out there, some of which seem to have better reliability than others when it comes to connection points. You can find plenty of videos online from professional plumbers to base your choice upon.

    So best wishes on your plumbing project.

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  4. #3
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    Re: Repipe- manifold vs trunk/branch

    I will say up-front I am not a PEX fan. My son recently replumbed his house with copper after having a serious leak leading to a mold issue in his crawl space from his PEX piping. Then he found it had been repaired previously. His neighbors have mostly had similar issues or worse. But one neighbor I talked to with him says his builder used a different PEX and he has no issues. So maybe there is good and bad PEX or maybe his neighbor just hasn't had a problem YET.

    I would definitely put in a manifold if I did PEX because I worry about the connections. That wasn't my son's issue, his cracked on hot water lines at bends. But it has been an issue on PEX before. If your only connections are at the two ends, at least you can see them.

    Copper takes a LOT longer and costs more. But there is an in-between choice, CPVC. I had a couple bathrooms plumbed last year due to the movement of the MBR and creation of a half bath. The plumber wanted to use PEX and I objected, not because I know there are issues with the current generation but because all previous generations have had issues. He did not want to do copper so I suggested CPVC. He had no issue with that. It took his helper an hour or so to run the CPVC lines for both bath rooms. I've done it myself and did the final plumbing for these two bathrooms. It is easy to work with. My previous house was nearly 15 years old with CPVC and my son's previous house was nearly 20 years old with CPVC and neither had any issue with it.

    If I ever have an issue with my CPVC I will run copper. I can get to all the CPVC in the crawl space so it wouldn't be terrible. The insulation is closed cell foam so a leak shouldn't do the kind of damage my son had. While copper takes 3 or 4 times as long (at least when I do it) I don't think anything else has the track record of copper. But I have one co-worker who has had leaks in thin walled copper. He is on a well and his water is probably acidic.

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    Re: Repipe- manifold vs trunk/branch

    When we were house hunting, one of the houses we looked at had a manifold system similar to that in your picture. It was a definite selling point for us. I really liked that concept. Should make troubleshooting problems easy - or just isolating a line to work on it without having to turn off the entire water supply.

    As you can tell, I'm a fan of the system.
    I don't believe in Astrology. I'm a Sagittarius and we're skeptical.

    "May the grain be with you" - Roy Underhill

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    Re: Repipe- manifold vs trunk/branch

    I replumbed our old house 17 years ago with cpvc - no problems thus far. Any rennovations or repairs I have done lately have been PEX from lowes. I like the manifold idea, but it isn't practical for our house. When I did the CPVC, i put in isolation valves for each bathroom so I could turn one off and have the rest of the house in service. That has been handy.

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    Re: Repipe- manifold vs trunk/branch

    Pex is the way to go. It is the most resilient and robust material for residential supply lines. I have built home using a plumbing manifold. The three primary reasons that the manufacturers stated for a manifold were that you could turn off individual fixtures from the manifold and that you could use smaller supply lines for most devices and it reduced the number of fittings, therefore reducing the risks of leaks at fittings.

    Despite all of the advertised cost savings, the manifold system cost about 20% more than the conventional system. The manifold system used more pex and the labor cost was higher. This is especially true if you are insulating your hot water lines. I never worry about leaks at fitting in pex systems. Pex connections are so reliable that fitting leaks are practically nonexistent. That pretty much leaves the advantage of a manifold system being that you can turn off each individual fixture from the manifold. When you think about it, you can generally isolate most fixtures in your home with a shut-off that is located at the fixture. The exception would be some tub and shower valves, most of which will have individual shut-off valves under the access plate, depending on the age of the home and how plumbing code was enforced.

    On a new home, using a manifold is a toss up. On a re-pipe, I would stick with a conventional piping plan, unless using a manifold would allow you to run the supply lines more easily or efficiently. A lot depends on whether the original plumber made up his joints in the crawlspace, where they are accessible, or whether he made up the joints in the walls. If there are a lot of joints in the walls, it might make going with a manifold system a better option.

    Pete

    Quote Originally Posted by redknife View Post
    My question for the group pertains to repiping the water supply hot and cold lines within our house. Should we use manifold home run or trunk and branch pipe configuration?

    Here are more details:
    We have polybutylene water supply pipes in our 1997 home. Polybutylene pipes represent a risk for spontaneous leak and rupture. Should this assertion cause controversy I’d like to avoid a polybutylene discussion. We are choosing to repipe rather than wait and see. Currently I am in the middle of refinishing the basement after foundation water intrusion remediation (separate issue). Because of exposure, I am considering repiping the basement and first floor with PEX so that the plumbing inspection for the current permit will cover the minor bathroom work and the repipe. We’d repipe the second floor maybe in a year or so.

    I am favoring a PEX manifold in the basement utility room, something like the Viega Manabloc https://www.viega.us/en/products/Cat...-manifold.html feeding individual “home-run” lines to all fixtures (1/2 or 3/8 depending on fixture). I believe that every line could be run between the manifold and fixture without any intervening fitting, owing to the space offered by truss floor design. We have need for about about 19 cold and 12 hot lines, so a 36 manabloc would suffice.
    The other option would be to repipe with trunk and branch. Many more fittings, tees, etc, but less line pulling and less space in the utility room.

    As an aside, copper is fine, I have done it, but I’ll be running pex.
    .
    Does anyone have an informed opinion about the general situation or the specific manifold/home runs vs trunk-branch choice?

    thanks
    Pete - KD4CQZ

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  12. #7
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    Re: Repipe- manifold vs trunk/branch

    I have lost count of the homes that I have built with PEX. It has been, by far, the most reliable plumbing supply line material that I have ever used. Of course, it does take some understanding of the material and how to use it, but PEX is about as idiot-proof as as a plumbing component gets. We always specified name-brand pipe, fitting, and crimp rings. I have seen plenty of problems with poly, first the acetyl fittings, then the aluminum fittings, then in the latter years the pipe itself failing. Residential copper plumbing lines were attacked by acidic soils, acidic water, and even not-so-close lightning strikes. CPVC is a viable supply line, but most plumbers hate it. Like any PVC product, it is prone to shattering and if it freezes with water in it, it will break - PEX is virtually immune to freezing. Plumbers don't like working with the solvents and solvent glues that PVC pipe requires. I have never used CPVC in any of the homes that I have built. Two of the homes had Poly, only because the client specified it.

    Most building codes do not allow joints in supply lines if the lines are run below a concrete slab. That applied to copper, poly, CPVC, and PEX. Some jurisdictions didn't enforce that rule for CPVC because it would be very difficult to run that material without joints under the slab. Other jurisdictions did not allow CPVC joints under a slab and that ruled out using CPVC in that type of construction.

    The new stainless steel PEX crimps are a lot easier to use than the previous generation of solid copper ring crimps. It takes less muscle to make a good crimp with the stainless crimps and the crimp tools are smaller too. You can get the new stainless crimp tools in much tighter spaces than the crimp tools for sold ring crimps.

    That said, CPVC is a viable plumbing supply material. Just as long as it does not freeze.

    Pete

    Quote Originally Posted by JimD View Post
    I will say up-front I am not a PEX fan. My son recently replumbed his house with copper after having a serious leak leading to a mold issue in his crawl space from his PEX piping. Then he found it had been repaired previously. His neighbors have mostly had similar issues or worse. But one neighbor I talked to with him says his builder used a different PEX and he has no issues. So maybe there is good and bad PEX or maybe his neighbor just hasn't had a problem YET.

    I would definitely put in a manifold if I did PEX because I worry about the connections. That wasn't my son's issue, his cracked on hot water lines at bends. But it has been an issue on PEX before. If your only connections are at the two ends, at least you can see them.

    Copper takes a LOT longer and costs more. But there is an in-between choice, CPVC. I had a couple bathrooms plumbed last year due to the movement of the MBR and creation of a half bath. The plumber wanted to use PEX and I objected, not because I know there are issues with the current generation but because all previous generations have had issues. He did not want to do copper so I suggested CPVC. He had no issue with that. It took his helper an hour or so to run the CPVC lines for both bath rooms. I've done it myself and did the final plumbing for these two bathrooms. It is easy to work with. My previous house was nearly 15 years old with CPVC and my son's previous house was nearly 20 years old with CPVC and neither had any issue with it.

    If I ever have an issue with my CPVC I will run copper. I can get to all the CPVC in the crawl space so it wouldn't be terrible. The insulation is closed cell foam so a leak shouldn't do the kind of damage my son had. While copper takes 3 or 4 times as long (at least when I do it) I don't think anything else has the track record of copper. But I have one co-worker who has had leaks in thin walled copper. He is on a well and his water is probably acidic.
    Pete - KD4CQZ

  13. #8
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    Re: Repipe- manifold vs trunk/branch

    Thanks for all of the detailed insight, Pete.

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    Re: Repipe- manifold vs trunk/branch

    Manifold is the way to go, if the home runs are done with a single (no joints) length of pipe. Every connector is a reduction in pipe size to 1/4" on half inch PEX. With the manifold, you have connection at manifold with cut off valve, along with connection at fixture, or area served. The only place I would have trouble with is in a seasonal home (cabin in the mountains) as mice tend to over winter in them, and will chew on plastic pipes and wires. There I would use copper, slopped to drain back, when the drain is opened in the fall.
    Last edited by junquecol; 07-20-2018 at 08:19 AM.

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