1215.3 Sizing Equations — 2025 California Plumbing Code

The inside diameter of smooth wall pipe or tubing shall be determined by Equation 1215.3(1), Equation 1215.3(2) and Table 1215.3 using the equivalent pipe length determined by the methods in Section 1215.1.1 through Section 1215.1.3. [NFPA 54:6.4]

LOW-PRESSURE GAS FORMULA (LESS THAN 1.5 psi)

[NFPA 54:6.4.1]

[Equation 1215.3(1)]

Q [0.381] D =

0.206

19.17 [(]

Δ H )

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 water column

Cr = in accordance with Table 1215.3

HIGH-PRESSURE GAS FORMULA (1.5 psi AND ABOVE)

[NFPA 54:6.4.2]

[Equation 1215.3(2)]

Q [0.381] D =

( P1 2 – P2 2 ) • Y 0.206

18.93 [[] 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

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 1215.3

Y = in accordance with Table 1215.3

Q [0.381] D =

0.206

18.93 [[]

( P1 2 – P2 2 ) • Y

Cr x L ]

Cr x L

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

TABLE 1215.3

Cr AND Y FOR NATURAL GAS AND UNDILUTED

PROPANE AT STANDARD CONDITIONS

[NFPA 54: TABLE 6.4.2]