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Thread: Best way to pipe in PEX/New bathroom?

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    DIY Junior Member nola mike's Avatar
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    Default Best way to pipe in PEX/New bathroom?

    Trying to get the supplies together for a remote 2nd home, so I don't know all the specifics I'm dealing with. I will be adding a sink and toilet, and relocating a shower. I was planning on using PEX for the first time, and wondering what size to use. I had planned on branching off of the existing 1/2" line, but researching appears that this won't be adequate, although right now I have no issues with water pressure. I'm not sure what my main supply line size is (obviously, I'll need to figure that out). Regardless, I won't be replacing the main line unless I have major issues--the rest of the pipes are easy enough to get to. Given that, IF I have a 1/2" main, would I be better off installing a PEX manifold with 1/2" ports, or using 3/4" PEX off of my existing 1/2" feeder? Or something different?

    Water pipe sizing
    Last edited by Terry; 11-13-2012 at 08:55 AM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Typically I run 3/4" on the cold for one bathroom and 1/2" for the hot.
    For two bathrooms, 3/4" on the cold and 3/4" for the hot. Or two fixtures, a tub and a lav on a 1/2" line.

    Water pipe sizing

    A one bath home can use 3/4" pipe
    Two bath requires 1" for the main
    Three bath requires 1" for the main, Depending on how many fixtures, this could also be 1-1/4"
    A four bath home requires 1-1/4" for the main.

    Last edited by Terry; 11-13-2012 at 09:15 AM.

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    DIY Junior Member nola mike's Avatar
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    So I'm at the second home now. As I suspected, the main is 1/2". Right now that is supplying 3 showers, 1 toilet, 3 sinks, a dishwasher, and a washer. There are zero water pressure issues. I'm wondering if it's partly because the house is one story...
    Anyway, I'll be adding a toilet and additional sink to this arrangement. I'll be cutting into the water line before it reaches 2 showers, 2 toilets, and 2 sinks (adding a sink and toilet to this branch, which is the end of the run). Am I better off installing a 3/4" manifold at this point and running 1/2" pex to each of the 6 fixtures, or teeing 2 new 3/4" pex lines off of the existing copper supply?

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    Forum Admin, Expert Plumber Terry's Avatar
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    1/2" is plenty for one plumbing fixture at a time. If you have two people in the home, that's when you would notice. Or perhaps having the washer cycle on while in the shower.

    Your question? Should your home be plumbed to code?

    I like doing things to code, it removes all that thinking and justifying as to whether I will ever have enough friends and family to justify correct plumbing if they all visit me.

    Water pipe sizing

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    DIY Junior Member nola mike's Avatar
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    Quote Originally Posted by Terry View Post
    1/2" is plenty for one plumbing fixture at a time. If you have two people in the home, that's when you would notice. Or perhaps having the washer cycle on while in the shower.

    Your question? Should your home be plumbed to code?

    I like doing things to code, it removes all that thinking and justifying as to whether I will ever have enough friends and family to justify correct plumbing if they all visit me.

    Water pipe sizing
    Luckily, I don't have that many friends :-)
    No, I understand that doing it to code is preferable. However, with a 1/2" main it just isn't feasable. The question is whether there would be less of a pressure drop using the PEX manifold system v. Teeing off the copper, or does it not matter?

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    Moderator & Master Plumber hj's Avatar
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    IN your situation, it doesn't matter.
    Licensed residential and commercial plumber

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by Terry View Post
    Thanks for the link. I wasn't aware that there was such a guide.

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    DIY Junior Member nola mike's Avatar
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    So I took another look at my main; it's 3/4", but for some reason reduced to 1/2" immediately upon entering the house. So I think that my plan will be to pipe 3/4" pex off of the 3/4" main. I'll tee off the existing 1/2" copper branches. At the end of the run (where the new fixtures will be), I'll run a 5 port 1" manifold with 1/2" pex branches supplying the new and old bathroom fixtures. Sound like a better solution?

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