1315.3 Sizing Equations — 2025 California Mechanical Code

The inside diameter of smooth wall pipe or tubing shall be determined by Equation 1315.3(1), Equation 1315.3(2) and Table 1315.3 using the equivalent pipe length determined by the methods in Section 1315.1.1 through Section 1315.1.3. [NFPA 54:6.4]

LOW-PRESSURE GAS FORMULA [LESS THAN 1.5 psi (10.3 kPa)]

[NFPA 54:6.4.1]

[Equation 1315.3(1)]

Q [0.381] D =

Δ H 0.206

19.17 ( Cr x L )

Where:

D = inside diameter of pipe, inches Q = input rate appliance(s), cubic feet per hour at 60°F and 30 inch mercury column L = equivalent length of pipe, feet Δ H = pressure drop, inches of water column

Cr = in accordance with Table 1315.3

Q [0.381] D =

19.17 (

Δ H

x L )

0.206

Cr x L

HIGH-PRESSURE GAS FORMULA [1.5 psi (10.3 kPa) AND ABOVE]

[NFPA 54:6.4.2]

[Equation 1315.3(2)]

Q [0.381] D =

( P 1 [2] – P 2 [2] ) - Y 0.206

18.93

[ Cr x L ]

Where:

D = inside diameter of pipe, inches

Q = input rate of appliance(s), cubic feet per hour at 60°F and 30 inch mercury column

P 1 = upstream pressure, psia ( P 1 + 14.7)

P 2 = downstream pressure, psia ( P 2 + 14.7)

L = equivalent length of pipe, feet

Cr = in accordance with Table 1315.3

Y = in accordance with Table 1315.3

For SI units: 1 cubic foot = 0.0283 m [3], 1000 British thermal units per hour

= 0.293 kW, 1 inch = 25 mm, 1 foot = 304.8 mm, 1 pound-force per square

inch = 6.8947 kPa, °C = (°F-32)/1.8, 1 inch mercury column = 3.39 kPa, 1

inch water column = 0.249 kPa

Q [0.381] D =

18.93

[

( P 1 [2] – P 2 [2] ) - Y

Cr x L ]

0.206

Cr x L

294 2025 CALIFORNIA MECHANICAL CODE

FUEL GAS PIPING

TABLE 1315.3

Cr AND Y FOR NATURAL GAS AND UNDILUTED

PROPANE AT STANDARD CONDITIONS

[NFPA 54: TABLE 6.4.2]