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Each flush tank water closet is rated at 2.5 fixture units. Four units equal 10 FU. According to UPC water distribution tables, a 1-inch branch line is required to handle 10 FU at standard pressure conditions. A 3/4-inch line would be insufficient, risking pressure drops during simultaneous flushing. Correct answer: C. 1 inch.

UPC water supply tables size service lines based on total fixture units. A system with 25 fixture units requires a minimum of 1-1/4 inch service at standard pressures and developed lengths. While smaller lines (1 inch) may serve fewer units, undersizing risks pressure drops and inadequate flow. Larger sizes (1-1/2 inch) would be unnecessary unless extra capacity is required. Proper sizing ensures balanced supply and code compliance. Correct answer: C. 1-1/4 inch.

Flushometer valves discharge large volumes of water quickly and require a 1-inch minimum supply line under the UPC. A 3/4-inch or smaller line cannot deliver the necessary flow and pressure. Correct answer: C. 1 inch.

UPC drainage load tables specify that a 6-inch vertical stack may carry up to 720 DFUs. Beyond this capacity, upsizing is required to ensure the stack can handle peak discharge without surcharge. Correct answer: C. 720 DFUs.

At 100 feet, a 2-inch pipe delivers ~608,000 BTU/hr, which is insufficient. A 2-1/2 inch pipe delivers ~1,150,000 BTU/hr, making it the correct choice for 1,000,000 BTU/hr. Correct answer: B. 2-1/2 inches.