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The maximum volume of water contained in hot water distribution pipes shall be in accordance with Section L 502.7.1 or Section L 502.7.2. The water volume shall be calculated using Table L 502.7.
L 502.7.1 Maximum Volume of Hot Water Without Recirculation or Heat Trace
The maximum volume of water contained in hot water distribution pipe between the water heater and any fixture fitting shall not exceed 32 ounces (oz) (946 mL). Where a fixture fitting shutoff valve (supply stop) is installed ahead of the fixture fitting, the maximum volume of water is permitted to be calculated between the water heater and the fitting shutoff valve (supply stop).
L 502.7.2 Maximum Volume of Hot Water With Recirculation or Heat Trace
The maximum volume of water contained in the branches between the recirculation loop or electrically heat traced pipe, and the fixture fitting shall not exceed 16 oz (473 mL). Where a fixture fitting shutoff valve (supply stop) is installed ahead of the fixture fitting, the maximum volume of water is permitted to be calculated between the recirculation loop or electrically, heat traced pipe and the fixture fitting shutoff valve (supply stop).

Exception: Whirlpool bathtubs or bathtubs that are not equipped with a shower are exempted from the requirements of Section L 502.7.
TABLE L 502.7
WATER VOLUME FOR DISTRIBUTION PIPING MATERIALS*
OUNCES OF WATER PER FOOT LENGTH OF PIPING
NOMINAL SIZE (inch) COPPER M COPPER L COPPER K CPVC CTS SDR 11 CPVC SCH 40 PEX-AL-PEX PE-AL-PE CPVC SCH 80 PEX CTS SDR 9 PE-RT SDR 9 PP SDR 6 PP SDR 7.3 PP SDR 11
3/8 1.06 0.97 0.84 NA 1.17 0.63 0.63 NA 0.64 0.64 0.91 1.09 1.24
1/2 1.69 1.55 1.45 1.25 1.89 1.31 1.31 1.46 1.18 1.18 1.41 1.68 2.12
3/4 3.43 3.22 2.90 2.67 3.38 3.39 3.39 2.74 2.35 2.35 2.23 2.62 3.37
1 5.81 5.49 5.17 4.43 5.53 5.56 5.56 4.57 3.91 3.91 3.64 4.36 5.56
11/4 8.70 8.36 8.09 6.61 9.66 8.49 8.49 8.24 5.81 5.81 5.73 6.81 8.60
11/2 12.18 11.83 11.45 9.22 13.20 13.88 13.88 11.38 8.09 8.09 9.03 10.61 13.47
2 21.08 20.58 20.04 15.79 21.88 21.48 21.48 19.11 13.86 13.86 14.28 16.98 21.39
For SI units: 1 ounce = 29.573 mL
* NA: Not Applicable
L 502.7.3 Hot Water System Submeters
Where a hot water pipe from a circulation loop or electric heat trace line is equipped with a submeter, the hot water distribution system downstream of the submeter shall have either an end-of-line hot water circulation pump or shall be electrically heat traced. The maximum volume of water in a branch from the circulation loop or electric heat trace line downstream of the submeter shall not exceed 16 oz (473 mL).
Where there is no circulation loop or electric heat traced line downstream of the submeter, the submeter shall be located within 2 feet (610 mm) of the central hot water system; or the branch line to the submeter shall be circulated or heat traced to within 2 feet (610 mm) of the submeter. The maximum volume from the submeter to each fixture shall not exceed 32 oz (946 mL).
The circulation pump controls shall comply with the provisions of Section L 501.4.

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