Section 23.1.1/Hydraulic Calculation Requirements
NFPA 13 Chapter 23 covers hydraulic calculations proving the sprinkler system can deliver the design density with the available water supply.
Hydraulically designed sprinkler systems must include calculations demonstrating that the available water supply can deliver the required design density (in gpm per square foot) over the design area (in square feet) to the most hydraulically demanding area. The calculation starts at the most remote sprinkler and works back to the water supply, adding friction losses, elevation changes, and hose stream allowances. The calculation must show the system demand point (total flow and required pressure) is within the available water supply curve.
Why this section exists
The hydraulic calculation is the mathematical proof that the sprinkler system works. Without it, there is no way to verify that the pipe sizes, sprinkler layout, and water supply combine to deliver adequate water to the fire. The calculation identifies the weakest point in the system (the most remote area with the highest friction losses) and proves that even this worst case receives the required water density.
What plan reviewers look for
Plan reviewers check the hydraulic calculation for the correct design criteria (density/area from Chapter 11), the most remote area identification, the pipe schedule matching the drawings, and the demand vs. supply comparison. They verify that hose stream allowances are included and that the water supply data is current (flow test within 12 months).
Common violations
Related NFPA 13 requirements
Chapter 11 provides the design criteria (density/area curves) for each hazard classification. Section 6.1 covers water supply requirements. Section 8.5.1 covers sprinkler spacing that affects the hydraulic calculation. Chapter 27 covers the information required on sprinkler shop drawings.