Pipe size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Yersmay, Feb 14, 2006.

  1. Yersmay

    Yersmay Writing, constructionDIY Member

    Sep 9, 2005
    writing, construction
    Los Angeles
    I have installed new copper under my house... It's a small house so I used 3/4 inch for all main lines and a small amount of 1/2 for risers.

    Now I have to run a new line from the street meter to the house foundation and connect it all. The connection at the street meter is 3/4. Would it make any difference to increase to a 1 inch line from the 3/4 inch street meter, have that run to the house foundation and reduce back down to 3/4? Does that increase performance or is it pointless?

    Thanks in advance.

  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    I would never run a 3/4" from the meter to the house.

    1" is always better.
    If you have more than one bath, is required that it be 1" or larger.
    Even with the 3/4" meter.



    Last edited: May 22, 2016
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  4. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    It Depends on Demand and Pressure

    The required size of pipe depends on flow demands, supply pressure, and length.

    A 1/2" pipe, which has an inside diameter of 0.622" (about 5/8") has a pressure loss of about 40 psi per hundred feet of length at 10 GPM.

    A 3/4" pipe has an inside diameter of 0.824" (about 13/16") and has a pressure loss of 10 psi per 100 feet at 10 GPM and 20 psi per 100 ft at 15 GPM.

    If the length of pipe from meter to your house is 50 ft, you will use 50% of those lossses.

    A 3/4 OD tube has an ID of about 5/8" so it is like a 1/2" pipe.

    If the street pressure is 100 psi, it probably doesn't matter except that you will notice more pressure loss when the washing machine cycle runs or your sprinkler system comes on. If your street pressure with no flow if only 50 psi, you probably want the larger pipe.
  5. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Aug 23, 2005
    I&C Engineer (mostly WWTP)
    Columbus, OH
    Supersize or Would you like 1in with that pipe for a few bucks more?

    FWIW, I have an old house with 1" galvanized from the city, reduced to 3/4 and then to 5/8 for the meter and then 1/2" throughout the whole house.

    Shower pressure is so-so to adequete (but its a rainfall too so that doesn't help). Simultanious shower and kitchen sink or toilet or bathroom sink sucks and if the washing machine is on, count anything else out.

    I've thought of replacing the easily accessable pipe with 3/4" but its just not really worth it in an old house that I'm going to see in few years.

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