TradeToolsFire protection · in the TradeTools app
Sprinkler Hydraulic Demand Calculator
Sprinkler and hose demand for a hazard classification and design area: the density from the NFPA 13 curves, the number of heads, flow per head from density × coverage, pressure per head from Q = K√P, and the total the water supply has to deliver.
NFPA 13-2022
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Worked example
Ordinary Hazard 2, 1,500 ft² remote area — how much water?
| Hazard classification | Ordinary Hazard Group 2 |
|---|---|
| Design area | 1,500 ft² |
| Sprinkler | K-5.6 |
| Coverage per head | 130 ft² (default) |
| Total water demand | 562 gpm |
|---|---|
| Design density | 0.20 gpm/ft² |
| Number of heads | 12 |
| Flow per head | 26.0 gpm |
| Pressure per head | 21.6 psi |
| Sprinkler demand | 312 gpm |
| Hose stream allowance | 250 gpm |
OH2 at 1,500 ft² is 0.20 gpm/ft² on the density/area curve. 1,500 / 130 rounds up to 12 heads at 0.20 × 130 = 26 gpm each; K-5.6 needs (26 / 5.6)² = 21.6 psi. 12 × 26 = 312 gpm for the sprinklers plus the 250 gpm hose allowance for ordinary hazard: 562 gpm.
How it's calculated
The table behind the number
The hazard class and design area locate the density on the NFPA 13-2022 density/area curves (Figure 19.3.3.1.1). The number of heads is the design area divided by the coverage per head, rounded up. Flow per head is density × coverage; pressure per head comes from Q = K√P for the selected K-factor. Sprinkler demand is heads × flow; the hose stream allowance for the hazard class comes from Table 19.3.3.1.2; the total is the sum.
- NFPA 13-2022, Figure 19.3.3.1.1Density/area curves by hazard classification
- NFPA 13-2022, Table 19.3.3.1.2Hose stream allowance and water supply duration
- Q = K√PSprinkler discharge for the K-factor
Questions
Before you trust the number
Is this a full hydraulic calculation?
No. It is the demand at the remote area — the starting point. Pipe friction loss, elevation and the supply curve are the hydraulic calculation proper, done in the design software or by hand with Hazen-Williams; the Head Loss calculator covers a single run.
Which edition?
NFPA 13-2022 numbering. The 2016 edition kept the same curves under Figure 11.2.3.1.1 — the values are the same, the citation is not.