WSFU Calculation Guide

Water Supply Fixture Units (WSFU) are a standardized measure of the hydraulic load that a plumbing fixture imposes on a water supply system. WSFU account for both the flow rate of a fixture and the frequency and duration of use. A single WSFU does not equal a fixed GPM value - the relationship is non-linear because of diversity factor.

Each plumbing code defines its own WSFU values: **IPC (Table E102.3(2))**: Separate cold and hot WSFU per fixture type, occupancy, and supply control. Example: Water closet (flush tank, private) = 2.5 cold WSFU; Lavatory (private) = 0.5 cold, 0.5 hot WSFU; Bathtub = 4 cold, 4 hot WSFU. **UPC**: WSFU values from UPC tables with separate vertical/horizontal drainage values. **NSPC**: NSPC-specific WSFU tables with values that differ from both IPC and UPC.

WSFU are converted to flow rates using official code tables. The conversion is non-linear: - **IPC Table E103.3(3)**: GPM for given WSFU, separate for flush tank and flushometer. - 1 WSFU -> ~3 GPM - 10 WSFU -> ~14 GPM - 30 WSFU -> ~23 GPM - 100 WSFU -> ~43 GPM The non-linearity means a building with 100 fixtures does not need 100x the pipe capacity of a single fixture.

For non-code-listed fixtures (e.g., dental chairs, specialized equipment), Plumbing Booster allows entering WSFU values or direct flow rates. Custom entries are used exactly as entered - the software does not convert or reinterpret user-entered custom equipment data.

Fixtures have separate cold and hot WSFU values. Plumbing Booster calculates cold and hot water pipe sizes independently, with separate materials, series, and velocity limits for each.

In the Wet Areas Configuration page, add fixtures from the code-specific fixture table. The software automatically looks up WSFU values, multiplies by count, sums per branch/riser/system, converts to flow rate, and uses the flow rate for pipe sizing.