Underground Fire Main Pipe Sizing Calculator

Size underground fire main piping per NFPA 24 using Hazen-Williams for fire protection water supply systems

Input Parameters

Results

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Minimum Pipe Diameter
in
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Selected Pipe Size
in
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Total Friction Loss
psi
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Flow Velocity
ft/s
Note: NFPA 24 governs underground fire service mains. Minimum pipe size is typically 6 inches for sprinkler supply and 8 inches for hydrant loops. C-factor selection must account for pipe age and material per NFPA 24 Table A.6.2.1.

Reference

Underground Fire Main Sizing (NFPA 24): Hazen-Williams: p = 4.52 × Q^1.85 / (C^1.85 × d^4.87) Solve for d: d = (4.52 × Q^1.85 / (C^1.85 × p_max))^(1/4.87) C-factors: 150 (PVC/HDPE), 140 (cement-lined DI), 130 (unlined DI), 100 (old CI) NFPA 24: minimum 6" for sprinkler supply, 8" for hydrant loops.