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All storage water heaters operating above atmospheric pressure shall be provided with an approved, self-closing (levered) pressure relief valve and temperature relief valve or combination thereof. The relief valve shall conform to ANSI Z21.22. The relief valve shall not be used as a means of controlling thermal expansion.
Relief valves shall be installed in the shell of the water heater tank. Temperature relief valves shall be so located in the tank as to be activated by the water in the top 6 inches (150 mm) of the tank served. For installations with separate storage tanks, the valves shall be installed on the tank and there shall not be any type of valve installed between the water heater and the storage tank. There shall not be a check valve or shutoff valve between a relief valve and the heater or tank served.
Temperature and pressure relief valves (or combinations thereof) and energy cutoff devices shall bear the label of an approved agency and shall have a temperature setting of not more than 200°F (93.3°C) and a pressure setting not exceeding the tank or water heater manufacturer's rated working pressure. Where a pressure rating of more than 150 psi (1034.25 kPa) is not necessary for the proper function of the domestic hot water system, the pressure rating of the relief valve shall be limited to 150 psi (1034.25 kPa). The relieving capacity of each pressure relief valve and each temperature relief valve shall equal or exceed the heat input to the water heater or storage tank, and shall have the AGA steam temperature rating clearly indicated.
The discharge from the relief valve shall be piped separately to an indirect waste receptor located inside the building. The discharge shall be piped full size and installed in a manner that does not cause personal injury or property damage and that is readily observable by the building occupants. The discharge from a relief valve shall not be trapped. The diameter of the discharge piping shall not be less than the diameter of the relief valve outlet. The discharge pipe shall be installed so as to drain by gravity flow and shall terminate atmospherically not more than 6 inches (150 mm) above the floor. The end of the discharge pipe shall not be threaded.
Relief valve discharge piping shall be of those materials listed in Section 18-29-605.5 for water distribution piping or shall be tested, rated and approved for such use in accordance with ASME A112.4.1. Piping from safety pan drains shall be of those materials listed in Table 18-29-605.5.
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