Stack vent size

Old 07-07-18, 05:14 AM
maarkr's Avatar
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Stack vent size

Sorry for all of my posts, but I need to get the entire plumbing built and ready for inspection as soon as I can.
Can I install a 3" stack up past the wc wye, reduce it to 2" to tie in the kitchen/ shower/ lav drain up to the attic, then open it up to 3" to go thru the roof (to prevent freezing in Maine)? or just run 3" all the way?
Old 07-08-18, 06:26 PM
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As long as this isn't the main stack, you can reduce it to 2" for the vent. 2" will handle the bathroom group and kitchen sink. Even if you up-size to 3" at the roof for freezing issues, it's still considered a 2" vent - so that's fine.

BUT, you still need a 3" (or 4") vent somewhere in the system. The main stack/vent needs to match the outgoing main drain size.

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