1/2 or 3/4 PEX for a pipe feeding a washing machine and tub/shower?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Canada_DIY_Plumber, Aug 17, 2021.

  1. Canada_DIY_Plumber

    Canada_DIY_Plumber New Member

    Joined:
    Aug 2, 2021
    Location:
    British Columbia
    I'm doing a bathroom reno and adding a washer/dryer. The pipe feeding the bathroom is a mix of 1/2" copper and 3/4" PEX. It enters the bathroom as 3/4 PEX and I am installing two shut-off valves in an access panel for the whole bathroom. After these shut-off valves, I need go up into the attic and then down into a plumbing wall to feed the washing machine and a tub/shower. I will feed the lav and toilet using a 1/2" PEX branch.

    My options for the run to the washing machine and tub/shower plumbing wall:
    A) 3/4" PEX and then split off to 1/2" PEX inside the plumbing wall for the washing machine and shower.
    B) 1/2" PEX to the plumbing wall and to each fixture.
    C) Two separate 1/2" PEX lines from the shut-off valve that go up through the attic to the washer/dryer and the tub/shower.

    My thought process:
    This space is for seasonal use only and will often go unoccupied for weeks or months. I like having one line to the plumbing wall that supplies the washer and tub/shower because then I can run the tub for a few minutes to thoroughly flush out most of that line after it has gone unused for a long period of time.

    Given that, running 3/4 seems wise because I imagine a 1/2 line would be more susceptible to dramatic pressure drops if someone is running a load of laundry while having a shower (even with the fancy pressure balancing valves of today.)

    Aside from a negligible increase in cost, the downside is that the 3/4 line will take longer to supply hot water for the shower in the morning.

    I'm leaning to option A but would appreciate any second set of eyes.
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    [​IMG]

    The chart for PEX below.

    [​IMG]
     
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  4. Canada_DIY_Plumber

    Canada_DIY_Plumber New Member

    Joined:
    Aug 2, 2021
    Location:
    British Columbia
    Thanks. In that second chart...
    I will have 6 fixture units for this run (shower + clothes washer).
    So it looks like it is saying my developed length will need to be less than 40 feet if I go with 1/2" and could be more than 40 feet if I go with 3/4"?
    This stuff will probably be within 30 feet developed length of the entry to the house.
     
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