(Adopted 6-19-97


101 PURPOSE: To limit the emission of nitrogen oxides (NOx) from natural gas-fired water heaters.




201 BRITISH THERMAL UNIT: The amount of heat energy required to raise the temperature of one pound of water from 590 F to 600 F at one atmosphere pressure

202 HEAT INPUT: The amount of heat energy released by natural gas burned in a natural gas-fired water heater. It is calculated during certification testing in accordance with the test method referenced in Section 502.

203 HEAT OUTPUT: The amount of heat energy, Ho, in British Thermal Units (BTU), absorbed by the water being heated during the process of natural gas-fired water heater testing in accordance with the protocol referenced in Section 502. It is calculated using the following equation:

204 JOULE: A unit of heat energy output equal to 9.4799 X 10-4 BTU

205 MOBILE HOME: A residential dwelling, designed and manufactured to be movable from site to site as desired by the owner/occupant, and that is not a Recreational Vehicle as defined in Section 211.

206 MOBILE HOME WATER HEATER: A natural gas-fired water heater manufactured exclusively for mobile home use.

207 NANOGRAM: A unit of mass equal to one billionth of a gram, or 10-9 gram

208 NATURAL GAS: A mixture of gaseous hydrocarbons containing at least 80 percent methane by volume as determined according to American Standard Test Method (ASTM) D1945-64.

209 NATURAL GAS-FIRED WATER HEATER: A closed vessel in which water is heated by the combustion of natural gas and is withdrawn for use external to the vessel at pressures not exceeding 160 psig, including the apparatus by which heat is generated and all controls and devices necessary to prevent water temperatures from exceeding 2100 F (990 C).

210 RATED HEAT INPUT CAPACITY: The heat input capacity specified on the nameplate of the combustion unit. If the combustion unit has been altered or modified such that its maximum heat input is different from the heat input capacity specified on the nameplate, the actual heat input capacity, as certified by the Manufacturer or Certified technician, shall be considered as the rated heat input capacity.

211 RECREATIONAL VEHICLE: A motor home, travel trailer, truck camper, or camping trailer, with or without motive power, designed for human habitation for recreational, emergency, or other occupancy, and which meets all of the following criteria:

  1. contains less than 320 square feet of internal living room area, excluding built-in equipment, including, but not limited to wardrobe, closets, cabinets, kitchen units or fixtures, and bath or toilet rooms;
  2. contains 400 square feet or less of gross area measured at maximum horizontal projections;
  3. is built on a single chassis and
  4. is either self propelled, truck mounted, or permanently towable on the highways without a permit.

212 STORAGE TANK CAPACITY: The capacity of the natural gas-fired water heater in gallons. It is calculated using the following equation:

213 SWIMMING POOLS AND HOT TUBS: (For the purposes of Section 103.4 of this rule) Residential only, single-dwelling, recreational and personal therapeutic equipment, including in-ground swimming pools, above-ground swimming pools, spas and hot tubs.


301 NITROGEN OXIDES EMISSION LIMIT: A person shall not distribute, offer for sale, sell or install, any natural gas-fired water heater within the District, unless it meets either of the following standards:


401 COMPLIANCE SCHEDULE: Effective January 1, 1998, no person shall distribute, offer for sale, sell or install any natural gas-fired water heater which does not comply with the requirements of Section 300.



403 MANUFACTURERS' LABELING REQUIREMENT: A manufacturer shall display the model number of the water heater complying with Section 300 on the shipping carton and on the rating plate of each water heater unit. The manufacturer shall also display the certification status on the shipping carton and on the water heater. A label stating "Certified per South Coast Air Quality Management District, Rule 1121" or equivalent language, will meet the shipping carton label requirement of this section.


501 RETENTION OF RECORDS: A manufacturer shall keep test data, calculations, reports and other certification records for as long as the water heater model is offered for sale or sold in the District, or for three calendar years after manufacture, whichever is longer. These records shall be made available to the Air Pollution Control Officer upon request.

502 TEST METHOD: Any natural gas-fired water heater distributed, offered for sale, sold, or installed within the District Shall be tested in accordance with the South Coast Air Quality Management District Protocol: "Nitrogen Oxides Emission Compliance Testing for Natural Gas-Fired Water Heaters and Small Boilers, January 1995".