Probable Peak Demand (WSFU to GPM)
Hunter's-curve probable peak flow in GPM from total water-supply fixture units, for flush-tank or flush-valve systems.
Example
You enter
- Total water-supply fixture units (WSFU) 120
- System type flush_valve
You get
- Probable peak demand 73
Checked against published worked examples from: Hunter's curve (NBS BMS65) / IPC 2021 Appendix E.
Details, formula, and sources
Formula or tablegpm = interpolate(curve, wsfu): piecewise-linear between published [WSFU, GPM] breakpoints for the selected system type (flush tank or flush valve). Flush-valve systems peak higher at low WSFU.
Source and editionHunter's curve (NBS BMS65, Methods of Estimating Loads in Plumbing Systems) and IPC 2027 Appendix E (Table E103.3(3), identical in 2021) by name; the curve ships as editable breakpoints read from that table.
Free accessIPC 2027 free read-only at codes.iccsafe.org; NBS BMS65 is public-domain (US government). The bundled curve carries the Table E103.3(3) values as editable breakpoints.
What governsEstimate. AHJ and licensed professional govern.
API field nameswsfu, system_type, gpm
- Demand curve editable [WSFU, GPM] breakpoints per system type, read from IPC Table E103.3(3)Hunter's curve / IPC 2027 Appendix E (identical in 2021)