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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.

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Upvote via reddit :) – Ether Oct 1 '10 at 21:00

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.

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