What is a standpipe system?

A standpipe system is a network of piping inside a building that delivers water to hose connections on each floor, allowing firefighters or occupants to fight fires without running long hose lines from outdoors. NFPA 14 governs standpipe installation and design in the United States.

What are Class I, II, and III standpipes?

Class I standpipes supply 2½-inch hose connections for fire department use only (250 GPM demand). Class II standpipes supply 1½-inch hose stations for occupant use (100 GPM). Class III combines both connection types (250 GPM combined demand). NFPA 14 specifies minimum residual pressures: 100 psi for Class I and III at the highest 2½-inch outlet, 65 psi for Class II.

What is the Hazen-Williams equation used here?

The Hazen-Williams formula estimates friction loss in water-filled pipes: P_f = 4.52 × Q^1.852 / (C^1.852 × d^4.87) × L, where Q is flow in GPM, C is the roughness coefficient (120 for steel, 150 for PVC), d is inside diameter in inches, and L is pipe length in feet. The result is pressure loss in psi.

How is elevation head calculated?

Elevation head (psi) = elevation change (ft) × 0.433 psi/ft. For water, every 2.31 feet of rise equals 1 psi of back-pressure. This must be added to the friction loss when determining the supply pressure needed to reach the highest hose outlet.

What residual pressure is required at hose connections?

NFPA 14 requires a minimum residual pressure of 100 psi at the highest 2½-inch hose connection for Class I and III systems. Class II systems require 65 psi at the highest 1½-inch outlet. Maximum pressure at any hose connection must not exceed 175 psi without a pressure-reducing device.

Does this replace a full hydraulic calculation?

No. This tool gives a quick single-path friction loss estimate using a straight-pipe Hazen-Williams model. A full NFPA 14 hydraulic calculation must account for fittings (equivalent length), multiple paths, and demand from all outlets operating simultaneously. Use this for early design checks; submit formal hydraulic calculations for permit review.

Standpipe Pressure Calculator

Enter flow demand, pipe size, elevation, and supply pressure to calculate friction loss, elevation head, and residual pressure at standpipe hose connections.

Standpipe System Inputs

Standpipe Class (NFPA 14)

Flow Demand (GPM)

NFPA 14: 250 GPM (Class I/III), 100 GPM (Class II)

Pipe Inside Diameter (inches)

Total Pipe Length (feet)

Straight-pipe length only; add equivalent lengths for fittings manually.

Hazen-Williams C Factor

Elevation Change (feet)

Vertical rise from supply reference to highest hose outlet. Negative = outlet is below supply.

Static Pressure at Supply (psi)

Available static pressure at water supply connection or pump discharge.

Fill in the inputs and click Calculate
to see standpipe pressure results.

Residual Pressure at Most Remote Hose Outlet

psi residual pressure

Supply Pressure

psi static at supply

Friction Loss

Elevation Head

Velocity (ft/s)

Pressure Balance

Item	Pressure (psi)

Friction loss (psi): P_f = 4.52 × Q^1.852 ÷ (C^1.852 × d^4.87) × L

Elevation head (psi): P_e = elevation (ft) × 0.433 psi/ft

Residual pressure: P_r = Supply − P_f − P_e

Velocity (ft/s): V = 0.4085 × Q ÷ d²

Reference: NFPA 14 (Standpipe and Hose Systems), Hazen-Williams equation for fire protection piping.

Summary

This calculator determines pressure requirements for Class I, II, and III standpipe systems per NFPA 14. Enter the total flow demand, pipe diameter, pipe length, elevation change, and available supply pressure to instantly compute friction loss using the Hazen-Williams equation, elevation head, and residual pressure at the most remote hose connection. All calculations run in your browser with no data sent to any server.

How it works

Select the standpipe class (Class I, II, or III) to set default flow demand and hose outlet size.
Enter the pipe inside diameter and total pipe length from the water supply to the most remote hose valve.
Enter the elevation difference between the water supply reference point and the highest hose outlet.
Enter the static pressure available at the water supply connection.
Click Calculate to see friction loss, elevation head, and residual pressure at the hose connection.
Review the pressure breakdown table to check whether your supply meets the NFPA 14 minimum residual pressure.

Use cases

Verifying that a building water supply meets NFPA 14 standpipe pressure requirements.
Sizing standpipe piping to limit friction loss for high-rise fire protection systems.
Comparing 4-inch vs 6-inch standpipe diameters for a given flow demand.
Pre-design pressure checks before running full hydraulic software.
Estimating pump pressure requirements for fire department connections.
Educational use in fire protection engineering and fire science coursework.
Checking pressure at intermediate hose connections in multi-story buildings.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu