SprinklerCalc.ca

THE HYDRAULIC TEXTBOOK FOR ONTARIO FIRE PROTECTION ENGINEERS
NFPA 13 / 14 / 20 Standards
Version 2026.1
Fundamental Physics
1. Sprinkler Discharge
2. Hazen-Williams Friction
3. Pipe Velocity
Water Supply
4. Water Supply (N1.85)
5. Elevation Head
System Design
6. Density/Area Demand
7. Hose Stream Allowance
8. Standpipe Demand
Seismic & Hardware
9. Seismic Forces (Fp)
10. Equivalent Lengths

Sprinkler Discharge (K-Factor)

Determines the flow rate (gpm) from a sprinkler head based on its orifice size and the pressure available.

Q = K · √P
Q: Discharge Flow Rate measured in Gallons Per Minute (gpm).
K: Discharge Coefficient (dimensionless). Common values: 5.6 (standard), 8.0, 11.2, 14.0, 25.2 (ESFR).
P: Residual Pressure at the sprinkler head orifice measured in Pounds per Square Inch (psi).

Reference: NFPA 13 Section 23.4.4.1.

Hazen-Williams Friction Loss

Calculates the pressure drop caused by the roughness of the internal pipe wall and fluid turbulence.

Pf = [ 4.52 · Q1.85 ] / [ C1.85 · d4.87 ]
Pf: Friction loss per foot of pipe (psi/ft).
Q: Flow rate through the pipe (gpm).
C: Friction loss coefficient. (Steel = 120, CPVC = 150, Wet Cast Iron = 100).
d: Actual internal diameter of the pipe (inches).

Fluid Velocity in Pipe

Ensures the water velocity does not exceed engineering limits to prevent water hammer and erosion.

V = 0.408 · Q / d2
V: Velocity (feet per second, fps). NFPA does not set a limit, but 20 fps is a common engineering practice limit.
Q: Flow (gpm).
d: Internal Diameter (inches).

Water Supply Analysis (N1.85 Method)

Predicts available pressure at any demand flow point based on a standard fire hydrant flow test.

Pr = Ps - (Ps - Pres) · (Qdemand / Qtest)1.85

Used to plot the "Water Supply Curve" on semi-exponential graph paper.

Elevation Head Pressure

Calculates the pressure gained or lost due to the weight of the water column in vertical piping.

Pelev = 0.433 · H
0.433: Pressure exerted by a 1-foot column of water (psi/ft).
H: Vertical height change (feet).

System Demand (Density/Area)

The primary method for determining the total water required for a specific floor area based on hazard level.

Qsystem = Density · Area

Example: Light Hazard = 0.10 gpm/sq.ft over 1500 sq.ft = 150 gpm base demand.

Equivalent Length Table

Converts friction loss from valves and fittings into an equivalent length of straight pipe.

Reference: NFPA 13 Table 23.4.3.1.1 (Schedule 40 Steel Pipe, C=120).