Manifold size vs Supply size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Garfield, May 17, 2011.

  1. Garfield

    Garfield semi-pro

    May 17, 2011
    Hello all, this is my first post here.

    I am doing a gut/remodel of a house built in 1942 or so. I have ripped out all the galvanized supply piping and will replace it with PEX.

    The water supply into the house and out of the meter is brand new 3/4" copper. My manifolds have 1" input and 1/2" valve outputs (10 hot/12 cold.)

    Which makes more sense:(from a flow point of view-not cost)
    A) put a 3/4 x 1 coupling at the meter outlet and run 1" to the manifold?
    B) Run 3/4" from the meter output to the manifold, and put a 3/4 x 1 coupling into the manifold's 1" input?

    Total length of meter to manifold is maybe 25' or so. So in A above I'd have 25' of 1", and in B I'd have 25' of 3/4".

    But in any case, the restriction is at the meter where it is 3/4". It's city water with good pressure (not measured, though.) To me it seems like six of one, half dozen of the other.

    Thanks for any help.

  2. SacCity

    SacCity In the Trades

    Mar 14, 2011
    Sacramento, CA
    The pressure and flow, will be a result or sum of all the pressure losses.
    So if you have four sections of pipe, Section A, B, C, D
    The loss will be the sum of those, If you replace a section of 3/4" line with 1" line then the resultant loss will be lower and you will have slightly better water flow and pressure.
    But to be honest 25 feet of straight line won't make much difference.
    If you are going to have to use an adaptor then make it at the meter. Can't hurt.
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  4. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Friction Loss

    Use 1" from the meter.
    The smaller the pipe, the more friction there is. And PEX is undersized anyway.
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