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Thread: shower vent can be 1.5"?

  1. #1
    DIY Member
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    Default shower vent can be 1.5"?

    the drain line for a shower is supposed to be 2", right? can it Tee to a 1.5" vent?

    my 1927 shower has 1.5" from the shower all the way to the 4" cast iron stack. i'm hoping that when i replace the drain line i'll be able to leave the vent in place. please tell me i don't have to replace that vent pipe.

  2. #2
    Plumbing Designer FloridaOrange's Avatar
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    Default

    As long as the shower is the only fixture being vented, 1-1/2" is acceptable.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default drain

    I do not know how you would make the reduction in size without creating a restriction. In any case a 1 1/2" drain pipe, especially if it is fairly long, will create a resistance and prevent maximum drainage.

  4. #4
    General Contractor Carpenter toolaholic's Avatar
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    Default never happen here!

    2"" unless you're dating the inspector. hay this is sf, ya never know

  5. #5
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    Default

    seems like the basic yes/no answer will have to come from my inspector.

    hj, could you please elaborate? did you mean 'vent pipe' rather than 'drain pipe'? or were you just commenting on how i probably don't get very good drainage now with my 1.5" drain line? the reduction you're referring to is going from 2" drain to 1.5" vent? the following paragraph hopefully gives a better picture. i understand that my 2" drain won't drain optimally with a 1.5" vent but it should be an improvement over 1.5" drain line, and if the inspector will be happy then i'll be happy.

    after the trap, the drain goes horizontal (with slope) about 1' to a Tee that has a vertical vent pipe that goes straight up through the attic and out the roof (about 20'). the drain line then goes horizontal another 2', then down 10', then horizontal (with slope) another 8' before it feeds into the main stack about 6' above the basement slab.
    my idea was to replace the drain line all the way back to the stack with 2", and re-attach to the existing 1.5" vent pipe by means of a reducing bushing just above a new Tee. i have plenty of vertical wiggle room in the joist cavity for the bigger pipe/fittings/bushing.
    oh and currently it's all galvanized back to the cast iron stack.
    is there any reason not to have at least a section of galvanized? that last horizontal run to the stack is only about 6' above the basement floor and i'm worried that plastic might succumb to, say, a 4-year-old whacking it with a broomstick. the basement is our playroom.

    thanks

  6. #6
    Plumber/Gasfitter dubldare's Avatar
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    Default

    What your saying sounds right. I don't feel you need to have metallic pipe for that bottom horizontal to the stack, unless your 4 year old is a real big bruiser, lol.

    An 1 1/2" vent is perfectly adequate for a shower, an 1 1/4" would suffice where I am; (although it must increase to 2" prior to penetrating the roof, here).

  7. #7
    Forum Admin, Expert Plumber Terry's Avatar
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    Default

    I always use a 1-1/2" vent for showers if I'm using plastic waste and vents.
    The trap and waste is 2".
    Most of the plastic fittings start at 1-1/2".

    If I'm using cast iron, then it's two inch, mainly because I'm not stocking the smaller stuff on the job.

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