12.4 Part 3 Worked Example: Sizing the Meter, Building Supply, and Every Branch with Table 610.4

The Column We Are Using

From Section 12.3: 58 psi, so the 46–60 psi range, and 140 feet, so the 150-foot column. Table 610.4, 46–60 psi, 150-foot column:

Step 1: Meter and Building Supply (610.8)

Load = 99.5 FU. Reading down the column: 4, 14, 28, 30, 39, 52, 66, 85, then 128. That row gives a 1-1/2-inch meter and street service and a 1-1/2-inch building supply. It satisfies the 3/4-inch minimum.

If the drawing states an existing 1-inch meter, the 1-inch rows (30, 52, 85, and 85 for 2-inch pipe) cannot carry 99.5 FU. The meter itself would have to be upsized, which is why the meter and supply are chosen together.

Step 2: Branches (610.9)

Section 610.9 sizes each branch from its own fixture units, the total developed length of the system (the same 150-foot column), and the meter size. Two limits bracket the answer:

• Upper limit: no branch needs to be larger than the building supply (1-1/2 inches here).
• Lower limit: the Table 610.3 minimum fixture branch size, and for flushometers, never smaller than the valve inlet (610.10).

Reading method: Stay in the same column. Find the smallest branch size whose fixture-unit value is at least the branch load, using rows for the installed 1-1/2-inch meter. For the small sizes (1/2, 3/4, and 1 inch), the table only lists 3/4-inch or 1-inch meters. Those smaller-meter rows are conservative for a building with a larger meter, so use them.

Observations:

• The flushometer water closet branch is 1-1/4 inches, not 1 inch. The 1-inch minimum in Table 610.3 is a floor. At 46–60 psi and 150 feet, 1-inch pipe carries only 28 or 30 FU, less than a flushometer's 40.
• The urinal branch is 1 inch, larger than its 3/4-inch minimum, for the same reason: 3/4 inch carries only 14 FU in this column.
• Hot branches are small because only three-quarters of each fixture's value lands on the hot side.

Step 3: Velocity and Special Cases

• Section 610.12 limits copper velocity to 8 ft/s cold and 5 ft/s hot, and 610.1 requires every design to stay within the code's maximum velocities.
• Flushometer tanks (pressure-assist tanks) are sized like flush tank water closets, not flushometer valves (610.11).
• Section 610.13 exempts engineered systems acceptable to the AHJ, minor alterations and additions where the AHJ finds the supply adequate, replacement fixtures, and piping that is part of fixture equipment.

The Complete Answer Set for the Example

If You Get Stuck

1. Recheck the occupancy column (public or private).
2. Recheck the flushometer count per section (40, 70, 90, 105, or 115 plus 10 each).
3. Recheck 1/2 psi per foot, not 0.433.
4. Confirm the length column is at or above the developed length.
5. Confirm the building supply is at least 3/4 inch and no branch exceeds the building supply.