supply lines for new shower

Discussion in 'Shower & Bathtub Forum & Blog' started by RobertZ, Mar 20, 2012.

  1. RobertZ

    RobertZ New Member

    Mar 6, 2012
    Southern California
    Hey all,

    I am in the process of adding a seperate shower into our masterbath. Currently we have 1/2" copper supply lines feeding a single vanity, a tub/shower combo, and the toilet. I was planning to T off the existing 1/2" copper lines and running new lines to the shower. The tub/shower combo will now be a stand alone soaker tub. The new shower will be on the other side of the room approximately 8 ft from the existing lines.

    Based on what I'm planning will I run into water pressure problems? Right now I believe we have water pressure of around 4-5 gpm. If it would help at all I could run 3/4" lines to the new shower or even redo all the bathroom lines to 3/4". Problem is I could only change the lines in the bathroom and not all the way to the heater.

    Thanks for the help!

  2. Hackney plumbing

    Hackney plumbing Homeowner

    Jan 6, 2010
    Your 1/2" copper is already undersized for the load without adding the shower. Increasing the size of the pipes to the shower to 3/4" will not help you enough to notice.

    You need to increase the main supply lines to 3/4" to the bath then branch off with 1/2" to the fixtures.

    As a rule of thumb I only run two fixtures on a 1/2" line.

    Water pipe sizing
    Last edited by a moderator: Mar 21, 2012
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    Since there will normally only be one person in the room at a time, or if two the other one will not be using a high flow fixture, there is adequate water. Increasing pipe sizes seldom makes any difference in flow, unless the lines are VERY long.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Flow rate and pressure are related, but not the same. A big soaking tub will still fill with a 1/2" line, but will take longer than if you had used 3/4" all the way from the supply. While you're waiting to fill it, it will cool off some, so you may need to start out a little hotter. Some valves have less resistance/restriction in them, and thus can flow all that the supply can handle, but some do restrict the flow. With a 1/2" line, you don't want more water velocity than about 5-6fps which works out to around your current figure for flow. If the water flows faster, especially on the hot side, your pipes are subject to internal erosion. The larger the pipe, the move volume you can flow. the size restricts max flow, not pressure, and pressure should be okay as long as you aren't trying to draw more than is available. As HJ said, the longer the pipe run, the more friction, which can restrict flow, but for practical purposes, you may not notice in a typical house. A larger pipe can support more fixtures, but if the total flow is kept within design, it doesn't matter what size is supplying the thing.
  6. RobertZ

    RobertZ New Member

    Mar 6, 2012
    Southern California
    Thanks everyone for the input. Sorry for the delayed response. Been out of commission the last few days. Running larger lines from the main is not really an option in my case but it sounds like I should be OK for my project. I had originally thought of adding a second rain shower head to the shower that we would occasionally run at the same time. Would this still be a possibility if I made sure the total flow rate of the two shower heads didnt exceed my supply lines?

    Thanks again everyone.
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