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Natural Gas Pipe Flow Rate Calculator

HVAC Systems and Components
Fluids Engineering and Design

Natural Gas Pipe Flow Rate Requirement Formulas and Calculator

See also: Appliance Natural Gas Pipe Flow Rate Capacities Tables

Preview: Natural Gas Pipe Flow Rate Requirement Calculator

For capacities of natural gas pressures less than 1.5 psig may be determined by the following equation from NFPA/IAS National Fuel Gas Code (NFPA Standard 54/ANSI Standard Z223.1):

Q = 2313 · d2.623 ( Δp / ( C · L ) )0.541


Q = flow rate at 60°F and 30 in. Hg, cfh
d = inside diameter of pipe, in.
Δp = pressure drop, in. of water
C = factor for viscosity, density, and temperature = 0.00354 · (t + 460) · s0.848 µ0.152
t = temperature, °F
s = ratio of density of gas to density of air at 60°F and 30 in. Hg
µ = viscosity of gas, (0.012 for natural gas, 0.008 for propane) L = pipe length, ft
2313 = conversion factor


1 in-water = 0.03612729 psi
1 psi = 27.67990484254466 inches water

Gas service in buildings is generally delivered in the low pressure range of 7 in. of water. The maximum pressure drop allowable in piping systems at this pressure is generally 0.5 in. of water but is subject to regulation by local building, plumbing, and gas appliance codes [see also the NFPA/IAS National Fuel Gas Code (NFPA Standard 54/ANSI Standard Z223.1)].

Where large quantities of gas are required or where long lengths of pipe are used (e.g., in industrial buildings), low-pressure limitations result in large pipe sizes. Local codes may allow (and local gas companies may deliver) gas at higher pressures (e.g., 2, 5, or 10 psig). Under these conditions, an allowable pressure drop of 10% of the initial pressure is used, and pipe sizes can be reduced significantly. Gas pressure regulators at the appliance must be specified to accommodate higher inlet pressures. NFPA/IAS (2012) provides information on pipe sizing for various inlet pressures and pressure drops at higher pressures. More complete information on gas piping can be found in the Gas Engineers’ Handbook (1970).



American Gas Association and National Fire Protection Association.