Drainage, Waste & VentQuestion 101 of 360
What is the minimum vent size for a 3 inch drain, using the half-diameter rule?
a.1-1/2 inch
b.2 inch
c.1-1/4 inch
d.3 inch
Explanation
Half of a 3 inch drain is 1-1/2 inch, which is also above the 1-1/4 inch absolute minimum, so 1-1/2 inch is the minimum vent size. A 1-1/4 inch vent is below half the drain diameter here. A 2 or 3 inch vent is larger than the minimum this rule requires.
Law Reference: 2022 California Plumbing Code (CPC) §904.0Practice all 360 questions free — no signup required.
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