Design & SizingQuestion 12 of 110
A vent must be sized at not less than one-half the diameter of the drain it serves, and never smaller than 1-1/4 in. What is the minimum vent size for a 3 in drain?
a.1-1/4 in
b.2 in
c.3 in
d.1-1/2 in
Explanation
Half of 3 in is 1-1/2 in, which is larger than the 1-1/4 in floor, so the minimum vent is 1-1/2 in. The half-diameter rule sets the size and the 1-1/4 in minimum only governs very small drains. A 4 in drain by the same rule would need at least a 2 in vent.
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