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  1. #1
    Join Date
    Jul 2011

    Default pex plumbing system with new home construction

    I am going to be having a new home built. It will be a single story home approx 2,000 sq ft with a full basement. I'm trying to plan out the best plumbing system and distribution design that makes the most sense. I am going with PEX. I was thinking about the home run system, but have also seen somewhere where someone preferred to have a modified version where there were a couple of manifolds that were closer to the fixtures rather than a single manifold, as it results in waiting a long time to get hot water to the faucets. I saw somewhere else where someone mentioned having a temperature sensitive recirculation valve so it will feel like I have hot water on demand. Anyone have any thoughts on what works best. Does a single manifold really produce a long wait time for hot water as compared to a traditional trunk and branch copper system found in most homes? I realize "long wait" can mean a lot of different things to people, so I'm not really sure if its a factor or not. Looking to get some opinions, as I'd like to be informed so I know that my plumber will be giving me the best design for me. By the way, the home will have 3 full baths. 2 of them will be very close together, the other will be on the other side of the home. I wouldn't anticipate any run being longer than 40-50 ft from the distribution manifold, which is yet to be determined where it will be located. Thanks

  2. #2
    Join Date
    May 2008
    Pacific Northwet

    Default Re: pex plumbing system with new home construction

    If you search these boards, you'll find plenty of debate on PEX vs. copper, so I won't get into THAT here.

    A manifold system will likely result in hot water getting to remote fixtures FASTER than a trunk/branch system, since the total volume of cold water that must be evacuated from the line is less since there are smaller pipes involved. However, in a trunk/branch system if one fixture recently used hot water, another fixture will receive it sooner since there is already some amount of hot water in the line.

    In a true trunk/branch system, you would have a single trunk line that gets progressively smaller as fixtures are tapped off of it. The trunk goes by each fixture, resulting in a relatively short line from the trunk to the fixture. In reality, most installations actually have branches off of branches.

    Implementing a recirculating system becomes much more difficult with a home-run manifold system than a trunk/branch system, as there is a "dead end" on each line that must be dealt with. The easy way to deal with this is to use a thermostatic valve at each fixture, redirecting the cooled water from the hot line back into the cold line, and having a recirc pump on the water heater.

    A recirc system on a trunk/branch system can be done the same way, or you can simply run a return line from the farthest fixture back to the water heater, where a recirc pump pumps it back into the cold supply at the WH. This is simplest with a true branch system; otherwise you would have to install multiple return lines and thermostatic valves.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

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