Sprinkler System Demand and Water Supply (NFPA 13)
From the discharge density on the floor to the water supply the system is designed around.
Example
You enter
- Design density (gpm/ft²) 0.2
- Hydraulic design area (ft²) 1500
- Hose-stream allowance (gpm) 250
- Required supply duration (min) 90
You get
- Sprinkler demand 300 gpm
- Total demand (with hose) 550 gpm
- Stored supply for duration 49,500 gal
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeSprinkler demand = density x design area, plus the inside/outside hose-stream allowance, held for the required duration to give the stored volume. An Ordinary Hazard Group 2 space at 0.20 gpm/ft^2 over 1,500 ft^2 plus 250 gpm of hose for 90 minutes needs 550 gpm and 49,500 gallons, the numbers that size the fire pump and the tank. The area/density screening demand; the full most-remote-area hydraulic calculation is a separate analysis. A design aid, not a stamped hydraulic submittal; a qualified fire-protection engineer and the AHJ govern.
Formula or tablesprinkler_gpm = density x design_area; total_gpm = sprinkler_gpm + hose_gpm; volume_gal = total_gpm x duration_min.
Source and editionNFPA 13 (Standard for the Installation of Sprinkler Systems), 2022, by name; the density / design-area / hose / duration levers come from the hazard classification and the density-area curves.
Free accessNFPA 13 is viewable free of charge through NFPA's online free-access reader; the density x area + hose x duration arithmetic is public.
What governsEstimate. AHJ and licensed professional govern.
API field namesdensity, design_area, hose_gpm, duration_min, sprinkler_gpm, total_gpm, volume_gal
- Hazard-class levers the density, design area, hose allowance, and duration all come from the hazard classification (Light 0.10/1,500/100/30; OH1 0.15/1,500/250/60-90; OH2 0.20/1,500/250/60-90), editable defaultsNFPA 13 (2022)
- Screening demand the area/density product is the area/density screening demand (not the NFPA 13 pipe-schedule method); the governing demand comes from a full most-remote-area hydraulic calculation with friction and elevationNFPA 13 (2022)
- Ordinary occupancies storage and special occupancies (ESFR, high-piled, in-rack) use their own density / area / duration criteria, not these defaultsNFPA 13 (2022)