Can I use a 1 1/2 vent for a toilet (3" drain) in CA (not a went vent, no other fixtures on it)?
Most of the info I have on code implies this would be OK, but one item I have says that a 1 1/2 vent can only serve 8 "non-WC" fixture units.
Upvote via reddit :) - Ether 12 years ago
In California, which is based on UPC, a 1-1/2" vent, properly installed, can vent a 3" toilet drain.
However, local codes can vary, so it's always a good idea to draw a diagram and get a permit, so they can inform you of any special rules or anything you may have missed.
How To Vent & Plumb a Toilet (in 2022)