Water-Supply Pressure Budget
Available residual at the critical fixture after elevation, meter, backflow, and friction losses.
Example
You enter
- Street pressure (psi, use the low) 60
- Critical fixture height above main (ft) 30
- Meter loss (psi) 8
- Developed-length friction loss (psi) 12
- Required fixture residual (psi) 8
You get
- Elevation loss 13.0 psi
- Available at fixture 27.0 psi
- Headroom above minimum 19.0 psi
Checked against published worked examples from: IPC 2021 Section 604 / ASPE PEDH Vol. 2.
Details, formula, and sources
ScopeAvailable residual at the critical fixture after elevation, meter, backflow, and friction losses, with a go/no-go verdict.
Formula or tableelevation_loss = fixture_height * 0.433; available = street_pressure - elevation_loss - meter_loss - bfp_loss - friction_loss; headroom = available - fixture_min; adequate = headroom >= 0. 0.433 psi per foot of water column.
Source and editionIPC 2027 Section 604 and the ASPE Plumbing Engineering Design Handbook Vol. 2 by name; first-principles pressure budget.
Free accessIPC 2027 free read-only at codes.iccsafe.org; the 0.433 psi/ft water-column constant is public.
What governsEstimate. AHJ and licensed professional govern.
API field namesstreet_pressure, fixture_height, meter_loss, friction_loss, fixture_min, elevation_loss, available, headroom
- Water column 0.433 psi per foot of elevationphysical fact (water density)
- Fixture minimum default 8 psi (lavatory, sink, shower); tank water closet 20, urinal valve 25, siphonic flushometer valve 35, blowout flushometer valve 45 psiIPC 2027 Table 604.3 (identical in 2021)