D.C. Mun. Regs. tit. 12, r. 12-E1017
Insert new Section 1017 in the Mechanical Code to read as follows:
General. Each hot water storage tank and automatic water heater shall be equipped with safety controls to prevent the temperature of the water in the tank from exceeding 200 °F (93 °C) and the pressure from exceeding the maximum allowable working pressure for which the tank is built. Each such unit shall be equipped with the following:
Pressure relief valves. Each pressure relief valve shall be of the lever lifting, spring-loaded type without disk on the pressure side of the valve. The valves shall be set to relieve at a pressure at or below the maximum allowable working pressure of the tank and shall be so arranged that they cannot be reset to relieve at a higher pressure than that stamped thereon.
Relief valve capacity. The pressure relief valve or valves shall have sufficient capacity to prevent the pressure in the tank from rising to more than 10 percent above the maximum allowable working pressure. The rated capacity of the valve or valves shall be equal to the maximum gross output of the heating unit installed. The gross output shall be determined from the data supplied on the manufacturer's nameplate or catalog data, or from the fuel input.
Labeling. Pressure relief valves shall bear the ASME symbol to indicate that they comply with the requirements of the ASME Code in regard to construction, testing and rating, and shall be plainly and permanently marked by the manufacturer in a way that the marking will be readable when the valve is installed and will not be obliterated in service. Pressure relief valves used on non-ASME approved, gas-fired equipment shall bear the seal or mark of an approved agency to indicate listing under the requirements of an approved testing agency. Pressure relief valves shall bear the ASME symbol for equipment using other fuels. The marking on pressure relief valves shall include the following information:
Valve size. No pressure relief valve shall be less than 3/4 inch (19 mm) standard pipe size.
Valve installation. Each pressure relief valve shall be installed in a vertical position, directly on the top of the tank, or if there is no opening available, on a fitting in the hot water service line, within 2 inches (51 mm) of the tank. Each pressure relief valve shall have a full size discharge pipe of non-ferrous metal, with an unthreaded open end, extended to an approved plumbing fixture or, if none is available, to within 6 inches (152 mm) of the floor. When the discharge pipe is over 1 inch (25 mm) in diameter it shall be supported and braced to prevent any strain being placed on the valve.
Multiple valves. If more than one relief valve is used, it shall be permissible to connect them to a manifold whose inlet pipe area shall be equal to the sum of the areas of the inlet openings of all the connected valves. There shall be no restriction to pipe cross sectional area on either the inlet or discharge side of the relief valve or valves, and there shall be no shut-off valve or check valve between the relief valve and the tank.
Temperature relief valves. Each temperature relief valve shall bear a label indicating approval and listing by ASME, and shall be approved by the Department.
Valve type and design. Each temperature relief valve shall be of the automatic self-closing type with a test lever and shall be designed to open at 200 °F (93 °C) or lower and be of sufficient capacity to limit the temperature to not over 200 °F (93 °C). The valve shall be non-adjustable and shall not be less than 3/4 inch (19 mm) standard pipe size.
Label. Each temperature relief valve shall bear a plate permanently attached, giving the following information:
Installation. Each temperature relief valve shall be installed in a vertical position on the top of the tank. Temperature relief valves shall be screwed directly into the tank without intervening fittings unless the dip tube extension type is used, in which case the tube shall project into the tank. If a fitting is used, it shall be of non-ferrous material. Each valve shall have a full size discharge pipe with an unthreaded open end, extended to within 6 inches (152 mm) of the floor or to an approved receptor fixture. There shall be no restrictions to pipe cross section area on either the inlet or discharge side of the relief valve, and there shall be no shut-off or check valve between the relief valve and the tank.
Combination temperature and pressure relief valve. When a combination temperature-pressure relief valve is used, it shall conform with the requirements of Section 1017 for pressure relief valves and for temperature relief valves. It shall bear the ASME symbol, meet the labeling requirements of Sections 1017.4 and 1017.8.2, and bear the symbol of the American Gas Association for the temperature relief element.
Aquastat. Each aquastat used on an automatic gas water heater shall be listed by the American Gas Association, unless provided as part of a complete American Gas Association approved unit, and shall operate to shut off the gas supply to limit the temperature of the heated water to not over 210 °F (99 °C).
Hot water heating systems. Hot water supply boilers, tankless heaters, electric heaters, immersion heating coils in boilers and any other type of heater shall be protected against excessive pressure, as provided herein.
Pressure gauge. Each hot water supply boiler and hot water storage tank shall be provided with a pressure gauge connected directly to the boiler or tank by means of non-ferrous pipe. A cock with a "tee" handle shall be placed in the pipe near the gauge. The gauge shall have a dial not less than 4 inches (102 mm) in diameter and shall be so located that it can be easily read from the floor. It shall be graduated to not less than one and one-half (11/2) times the maximum allowable working pressure of the boiler or tank. Gauges shall not be required for range boilers and domestic type water heaters.
Thermometer. Each hot water supply boiler, hot water storage tank, tankless heater, immersion type heater or any other type of heater shall be provided with a thermometer capable of providing readings up to 300 °F (149 °C), of a size and so located that it can be easily read from the floor. It shall be located in a well so that it will indicate the temperature of the water at or near the outlet and shall be accurate within 2 percent. Thermometers shall not be required for range boilers or domestic type water heaters.
Water mixing valve. When hot water is used by the general public or by persons not in control of the heating equipment, an approved water mixing valve shall be installed to limit the temperature of the water at the fixtures to not over 140 °F (60 °C). A thermometer shall be installed on the discharge side of the mixing valve and shall be of a size and so located as to be easily read from the floor.
D.C. Mun. Regs. tit. 12, r. 12-E1017