Another kitchen sink vent question -vent size

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by rich6705, Apr 3, 2021.

  1. rich6705

    rich6705 New Member

    Joined:
    Mar 29, 2021
    Occupation:
    VA Social Worker
    Location:
    Pittsburgh
    So now that I know that I can tie my 1st fl. kitchen sink vent into the 2" steel vent used for the basement laundry tub, I'm going to follow breplum's suggestion of replacing the exposed steel vent pipe in the kitchen and basement with plastic.

    Can I replace the 2" steel vent with 1-1/2" ABS, or does it have to stay 2"? Using 1-1/2" would keep the vertical vent clearly behind the face of the wall stud. Because of how it was originally installed 100 years ago, it sticks out a little bit from the face of the stud and that section of the old kitchen wall was built around it.

    Also, can I use 1-1/4" ABS to tie the kitchen sink vent into the laundry tub vent, or does it have to be a larger diameter? Using the 1-1/4" would reduce the size of the hole I'd have to drill through a 3-1/2" deep wall stud.

    This vent will only be used for the basement laundry tub and 1st fl. kitchen sink. Can both, one, on none of these options be done? Many thanks for your help!
     

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  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Looking at the geometry, I don't see the upside to replacing the 2" galvanized with 1-1/2" ABS? Seems like 2" ABS would fit just as well and avoid the reducers and all.

    As to 1-1/4" ABS, it doesn't exist, you'd have to use 1-1/4" PVC or Copper. There is a very small advantage to using 1-1/4" Copper, as the OD is 1-3/8", so you could fit it through a slightly enlarged 1-3/8" hole in your stud. Which is under the allowable hole size for a bearing wall, so you wouldn't need to reinforce it. [40% of the width, which for a 3.5" wide stud is 1.4".]

    But that's totally not worth it for one stud. Just use 1-1/2" ABS and install a Simpson HSS2-SDS1.5 stud shoe around the hole.

    Cheers, Wayne
     
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  4. rich6705

    rich6705 New Member

    Joined:
    Mar 29, 2021
    Occupation:
    VA Social Worker
    Location:
    Pittsburgh
    Thank you Wayne for your advice! Especially the tip on the the Simpson stud shoe.
     
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