What size stack for a washing machine?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by cwolters, Jan 7, 2005.

  1. cwolters

    cwolters New Member

    Jan 7, 2005
    I am finishing out the plumbing for a basement bathroom. I had someone come do the drains for the shower, sink and stool in the floor. I am doing the above floor work. A drain that was not changed is from the utility tub that the washing machine currently drains into. I want to relocate the washing machine by about 2 feet and the current utility tub by a further 3 feet. I was going to put a 2" copper stack from about 6 inches above floor level up to about 48-50 inches for the washing machine to drain into. The concern I have is that the current drain that goes into the floor for the utility tub (which I will still tie into due to location) is 1-1/4" copper and I wonder if it is too small.

    Right now, I have two choices: work with 1-1/4 copper coming out of floor, run a trap just above the floor then switch to 2" copper after the trap and y to the sink (also having it's own trap) and the washing machine stack.

    The other choice may be to dig out the existing 1-1/4 and replace it with 2" but I don't know how far under the floor it goes as 1-1/4 and it could be up to 6 feet (in which case I will opt from doing it and risk it?)

    My concern is the volume of a washing machine going into the pipe and if it will overflow. There will be more than a 3/4" air gap in the stack to the inlet pipe so it should vent, I am just worried about necking it down like it is.

    What should I look at, or can I test it somehow before making the decision?

    Thanks in advance.

    Oh yeah, I live in SE Michigan.

  2. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    There is not even any doubt that it will overflow. Your 1 1/4" drain, if you have the size correct is only about 1/3 the size of a 2" pipe, and therefore it is much too small for a current washing machine drain.
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  4. Bob's HandyGuy

    Bob's HandyGuy Senior Member

    Sep 10, 2004
    Have you considered draining the machine into the utility tub?
  5. cwolters

    cwolters New Member

    Jan 7, 2005
    I did have it drain in the tub previously, my wife and I were trying to get away from that though. We don't use the utility tub downstairs and we were looking at smaller tubs that would still hold the capacity of most washers, but I wanted to put in a direct drain.

    Now I have made a huge discovery... The drain from the upstairs sink is on the other side of the wall - I have some questions, but it will solve my problem of volume capaciyt since it is 2" copper. I will post it in a different topic though.

  6. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    Washer drain

    A washer should have a 2" drain because a washer pumps mega amounts of water in a very short time. I know some may be getting by with a 1-1/2", but that's crowding the limits, especially with newer machines that drain faster than the older machines.
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