Pressure Analysis Methodology

A plumbing system must deliver adequate pressure at every fixture outlet. Pressure analysis verifies that the available supply pressure is sufficient to overcome static head (elevation), friction losses, and still meet the minimum fixture outlet pressure required by code.

Pressure analysis follows the IPC tabular method (Appendix E103.3): 1. **Determine required fixture pressure** - From IPC Table 604.3 for the most hydraulically remote fixture. 2. **Add static head loss** - Elevation difference x 0.433 psi/ft (or 9.81 kPa/m). 3. **Add meter loss** - Pressure loss through the water meter. 4. **Add tap/tee losses** - Pressure loss at the service tap. 5. **Add friction losses** - Hazen-Williams with material-specific C-factors. 6. **Sum total required pressure** - Compare to available pressure. 7. **If deficient** - Booster pump recommended.

Key fixture pressure requirements at the fixture outlet: - Water closet, flushometer (blow out): 45 psi - Water closet, flushometer (siphonic): 35 psi - Water closet, tank type: 20 psi - Urinal, flushometer valve: 25 psi - Shower (thermostatic/balanced): 20 psi - Bathtub (thermostatic/balanced): 20 psi - Lavatory, sink, standard fixtures: 8 psi Flushometer-valve fixtures require significantly higher pressures than tank-type fixtures.

A 5-story building with flushometer valves: - Most remote fixture: Water closet (siphonic) on 5th floor - Required fixture pressure: 35 psi - Static head (49 ft): 49 x 0.433 = 21.2 psi - Water meter loss: 3.5 psi - Tap loss: 1.5 psi - Friction losses: 8.0 psi - **Total required = 35 + 21.2 + 3.5 + 1.5 + 8.0 = 69.2 psi** If municipal supply is 60 psi -> deficient by 9.2 psi -> booster pump recommended. If municipal supply is 75 psi -> adequate.

When IPC method + Municipal supply are selected, an IPC Pressure Analysis section appears in System Structure. Enter municipal supply pressure, select pipe roughness and water meter size. The System Summary shows static pressure, total losses, residual pressure, and compliance status. If inadequate, a booster pump is recommended with the pressure deficit shown.