Supply sizing

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by bhavenst, Sep 30, 2004.

  1. bhavenst

    bhavenst New Member

    Sep 24, 2004
    I'm adding a bathroom (tub/shower, sink, toilet) in the basement. Our supply pipes are 3/4" to the main floor bathroom, after which they drop to 1/2" to supply the kitchen. Can I branch off the 1/2" (for a total of about 20' of 1/2" leading to the bathroom) to supply the bathroom, or do I have to replace it with 3/4"?
  2. e-plumber

    e-plumber DIY Senior Member

    Sep 1, 2004
    New York
    I would suggest bringing 3/4" copper lines to the new bathroom. I always pipe fixtures 3/4" to the second to last fixture, then reduce to 1/2".
    I believe recent code changes here permit (2) fixtures on one half inch line but I have not changed the way I've been doing it for years.
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  4. Deb

    Deb Plumber

    Sep 5, 2004

    No, 1/2" is meant for 2 fixtures, IMHO. Regardless, you are way over fixture units for a 1/2" line, no matter what code you are under and how much they have lowered it for water saver things. You are over with both hot and cold. I think that a 3/4" hot should be run too and then branch off the 3/4 with a 1/2 for the bathroom and a 1/2 for the kitchen sink and DW. Buy a good quality pressure balance valve for the tub/shower.
    The Pipewench
  5. bhavenst

    bhavenst New Member

    Sep 24, 2004
    That's what I was afraid of. I guess I'll go pick up some 3/4"!

    Thanks for the input...

  6. Chris

    Chris New Member

    Sep 17, 2004
    1/2" vs. 3/4" for bathrooms

    Isn't 1/2" better for the hot water line to the bathroom if there are only a tub and lavatory on the line? With 3/4" the waiting time for hot water to reach the bathroom can be substantially increased. Or is 1/2" too small to provide adequate flow? I know the UPC allows 4 fixture units on a 1/2" line, which is more than a tub (2fu) and lavatory (1fu) but then, code is a minimum, not a maximum.

    I've seen this done both ways on the various houses I've owned and was wondering if there was a consensus amoungst our pros here.
  7. LonnythePlumber

    LonnythePlumber Plumber, Contractor, Attorney

    Sep 6, 2004
    Plumber, Contractor, Attorney
    Wichita, Kansas
    1/2" Hot

    I'm one of those that runs 1/2" hot to supply a tub and a lavatory faucet. I do this so that the water does not have to run so long before it gets hot. However I know I am in a minority view and most run hot like they do cold which is 3/4" to the last two fixtures.
  8. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    Agree with Lonnie

    I tried a 3/4" supply line for my hot water and found it took forever to purge the cold water from the line. Pulled the 3/4" and replaced with 1/2". Much improved. No big difference in flow, very adaquate.
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