RULE 246 NATURAL GAS-FIRED WATER HEATERS

Adopted 6-19-97 

CONTENTS

100 GENERAL

101 PURPOSE 

102 APPLICABILITY 

103 EXEMPTIONS 

200 DEFINITIONS

201 BRITISH THERMAL UNIT 

202 HEAT INPUT 

203 HEAT OUTPUT 

204 JOULE 

205 MOBILE HOME 

206 MOBILE HOME WATER HEATER 

207 NATURAL GAS 

208 NATURAL GAS-FIRED WATER HEATER 

209 NANOGRAM 

210 RATED HEAT INPUT CAPACITY 

211 RECREATIONAL VEHICLE 

212 STORAGE TANK CAPACITY 

213 SWIMMING POOLS AND HOT TUBS 

300 STANDARDS

301 NITROGEN OXIDES EMISSION LIMIT 

400 ADMINISTRATIVE REQUIREMENTS

401 COMPLIANCE SCHEDULE 

402 CERTIFICATION REQUIREMENT 

403 MANUFACTURERS= LABELING REQUIREMENT 

500 MONITORING AND RECORDS

502 RETENTION OF RECORDS 

501 TEST METHOD 

Placer County APCD 246 - 1 Rules and Regulations 
This Page Intentionally Left Blank 

Rules and Regulations 246 - 2 Placer County APCD 
100 GENERAL

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

heaters. 

102 APPLICABILITY:

 102.1 Geographic: The provisions of this rule apply to all of Placer County. 

 102.2 General: This rule shall apply to any person who manufactures, distributes, offers for 

sale, sells, or installs any natural gas-fired water heater with a rated heat input 

capacity less than 75,000 British Thermal Units per hour (BTU/hr), for use in this 

District. 

103 EXEMPTIONS: 

 103.1 Exemption, Large Natural Gas-Fired Water Heaters: Water heaters with a rated heat 

input of 75,000 BTU/hr or greater are exempt from all provisions of this rule. 

 103.2 Exemption, Recreational Vehicles: Natural gas-fired water heaters used in 

recreational vehicles are exempt from all provisions of this rule. 

 103.3 Exemption, Swimming Pools and Hot Tubs: Natural gas-fired water heaters used 

exclusively to heat swimming pools and hot tubs are exempt from all provisions of 

this rule. 

 103.4 Exemption, Other Fuels: Water heaters using any fuel other than natural gas are 

exempt from all provisions of this rule. 

200 DEFINITIONS

 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: 

 Ho = MCpi ( Tdel - Tin ) + Vst Dn Cp2 ( Tmax - To ) 

 Where: Ho = Heat output, in BTU 

 M = Mass of the water withdrawn, in pounds 

 Cpi = Specific heat of water at the average temperature 

[(Tdel + Tin) / 2 ], BTU per pound per o

F 

 Tdel = Average delivery temperature, o

F. 

 Tin = Average inlet temperature, o

F. 

 Vst = Storage tank capacity, in gallons, as determined in Section 212 

 Dn = Density of water at the average temperature [(Tmax + To)/2], 

pounds per gallon 

Placer County APCD 246 - 3 Rules and Regulations 
 Cp2 = Specific heat of water at the average temperature, 

 [(Tmax + To)/ 2], BTU per pound per o

F. 

 Tmax = Maximum mean tank temperature recorded after cutout following 

the test draw, o

F. 

 To = The maximum mean tank temperature recorded prior to the test 

draw, o

F. 

 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:

 Vst = (Wf - Wt) / Ds 

 Where: Vst = Storage capacity of the water heater, in gallons 

 Wf = Weight of the water heater completely filled with water, in pounds 

 Wt = Weight of the empty water heater, in pounds 

 Ds = Density of water at the test temperature, in pounds per gallon

Rules and Regulations 246 - 4 Placer County APCD 
 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. 

300 STANDARDS

 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: 

 301.1 A natural gas-fired water heater that emits less than or equal to 40 nanograms of 

nitrogen oxides [calculated as NO2] per joule (93 pounds per billion BTU) of heat 

output; and is certified in accordance with Section 402. 

 301.2 A mobile home natural gas-fired water heater that emits less than or equal to 50 

nanograms of nitrogen oxides [calculated as NO2] per joule (116 pounds per 

billion BTU) of heat output; and is certified in accordance with Section 402. 

400 ADMINISTRATIVE REQUIREMENTS

 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. 

 402 CERTIFICATION REQUIREMENT:

 402.1 A manufacturer of any natural gas-fired water heater subject to Section 300 shall 

submit to the Air Pollution Control Officer (APCO) at least 30 days prior to sale, a 

statement obtained from an independent testing laboratory, certifying that the 

laboratory tested the unit in accordance with the method in Section 502 of this 

rule, and that it is in compliance with the provisions of Section 300. The 

statement shall be signed and dated, and shall attest to the accuracy of all 

information. The statement shall include the brand name, model number, the 

heat input capacity rating as it appears on the water heater rating plate, and test 

results in accordance with Section 502; 

OR

 402.2 A manufacturer shall submit to this District an approved South Coast Air Quality 

Management District (SCAQMD) certification obtained from an independent 

testing laboratory. Any model of natural gas-fired water heater certified as 

complying with the SCAQMD Rule 1121 prior to July 1, 1995, need not be 

recertified to the test protocol specified in Section 502 until such time as required 

by the SCAQMD. 

 402.3 A manufacture shall submit a new certification or certification statement meeting 

the requirements of Section 402.1 or Section 402.2 for any natural gas-fired 

water heater, the design of which is changed in any manner which may alter the 

emissions from the water heater. New certifications or certification statements, 

for either altered or new models, shall be submitted to the APCO at least 30 days 

before the water heater is offered for sale in the District. 

 

Placer County APCD 246 - 5 Rules and Regulations 
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. 

500 MONITORING AND RECORDS 

 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".

Rules and Regulations 246 - 6 Placer County APCD