A 4-inch drain serves 100 fixture units, and the vent serving it has a developed length of 150 feet. Using the UPC's Table 703.2 vent columns, what is the minimum vent diameter?
Not quite. The answer is C: 4 inch
The vent must be at least half the drain's diameter (2 inches here), but the load decides it. A 2-inch vent is rated for 24 FU and a 3-inch vent for 84 FU — both below 100 FU — while a 4-inch vent is rated for 256 FU and 300 feet, which covers the load and the 150-foot run. The trap is picking the 3-inch vent because 84 FU feels close; it is still under 100.
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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