A vent serves a 2-inch drain carrying 20 fixture units, and the vent's developed length is 100 feet. Using the UPC's Table 703.2 vent columns, what is the minimum vent diameter?
Not quite. The answer is C: 2 inch
A vent must be at least 1¼ inches and at least half the drain's diameter (1 inch here), so the floor is 1¼ inches — but load and length both govern. A 1½-inch vent is limited to 8 fixture units (and 60 feet), far short of 20 FU; a 2-inch vent is rated for 24 FU and 120 feet, which covers both the load and the 100-foot run. So 2 inches is the smallest vent that works.
Reference: UPC 2021 Table 703.2 (vent columns); §904.1 (Size and length of vents)
Checked against the official text
Table 703.2 is not supplied at the exam desk and must be memorized. The 2015 edition's vent columns were not read directly for this question; confirm against your 2015 book.
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