The main riser in the isometric below carries a combined 16 WSFU load. Under the UPC, can a plumber determine the minimum riser pipe size from that WSFU total alone, without knowing the available street pressure?
2ND FLOOR BRANCH (8 WSFU)
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1ST FLOOR BRANCH (8 WSFU)
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MAIN RISER
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WATER METER
Two-floor water riser
Not quite. The answer is B: No — UPC Table 610.4 sizes pipe using WSFU together with the available pressure range and the meter/building-supply size; the same WSFU total can require a different pipe size depending on the pressure range
Table 610.4 is genuinely three-dimensional: the same 16 WSFU load sized at a low pressure range (30-45 psi) needs a larger pipe than the identical load at a high pressure range (over 60 psi), because more available pressure can push the same flow through a smaller pipe. A WSFU total by itself, without knowing the pressure range the riser will see, isn't enough information to name a single correct diameter.
Reference: UPC 2021 Table 610.4; §610.8 (Fixture Unit Table for Determining Water Pipe and Meter Sizes)
Checked against the official text
The exam supplies this table at the desk, so the edition it prints is the one that counts on test day.
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