PROPOSED November 14, 2013 

4308 - 1 Proposed Amendments to Rule 4308 

RULE 4308 BOILERS, STEAM GENERATORS, AND PROCESS HEATERS – 0.075 

MMBtu/hr to less than 2.0 MMBtu/hr (Adopted October 20, 2005, Amended 

December 17, 2009, Amended [rule adoption date]) 

 

1.0 Purpose 

 The purpose of this rule is to limit emissions of oxides of nitrogen (NOx) and carbon 

monoxide (CO) from boilers, steam generators, process heaters and water heaters. 

2.0 Applicability 

 

 This rule applies to any person who supplies, sells, offers for sale, installs, or solicits the 

installation of any boiler, steam generator, process heater or water heater with a rated heat 

input capacity greater than or equal to 75,000 British thermal units per hour and less than 

2,000,000 British thermal units per hour. 

3.0 Definitions 

3.1 APCO: the Air Pollution Control Officer of the San Joaquin Valley Unified Air 

Pollution Control District, or any person authorized to act on behalf of the APCO. 

 3.2 Boiler, Steam Generator or Water Heater: any external combustion equipment 

fired with any liquid or gaseous fuel to produce hot water or steam. 

3.3 British Thermal Unit (Btu): the amount of heat required to raise the temperature 

of one pound of water from 59o F to 60o F at one atmosphere. 

3.4 California Public Utility Commission (PUC) Quality Natural Gas: any gaseous 

fuel, gas-containing fuel where the sulfur content is no more than one-fourth (0.25) 

grain of hydrogen sulfide per one hundred (100) standard cubic feet and no more 

than five (5) grains of total sulfur per one hundred (100) standard cubic feet. PUC 

quality natural gas also means high methane gas of at least 80% methane by 

volume. 

3.4 3.5 Certified Retrofit Kit: any burner, ancillary controls or blowers that have been 

demonstrated to comply with the provisions of this rule in Section 6.1, on a retrofit 

basis, on a particular model of unit. 

3.5 3.6 District: as defined in Rule 1020 (Definitions). 

3.6 EPA: United States Environmental Protection Agency. 

 

 3.7 Heat Output: the enthalpy of the working fluid output of the unit. 
PROPOSED November 14, 2013 

4308 - 2 Proposed Amendments to Rule 4308 

3.7 3.8 Higher Heating Value (hhv): the total heat liberated per mass of fuel burned (Btu 

per pound), when fuel and dry air at standard conditions undergo complete 

combustion and all resulting products are brought to their standard states at 

standard conditions. 

3.8 Hot Water Pressure Washer: for purposes of this rule, high-pressure cleaning 

machine in which the hot water discharge line (spray nozzle) is hand supported and 

intended for commercial and industrial applications. 

3.9 Humidifier: a device or system that uses an air stream heated by a direct contact 

combustion process in combination with a water spray to produce warm air of high 

humidity in order to maintain or increase the moisture content of the material being 

processed or conveyed by the air stream. For the purpose of this rule, such a 

device is not considered a boiler, steam generator or process heater. 

3.10 Instantaneous Water Heater: a water heater with a rated heat input capacity per 

hour that heats water only when it flows through a heat exchanger. 

3.11 Manufactured Home: as defined in 42 United States Code Section 5402 and 

California Health and Safety Code Section 18007. 

3.12 NOx Emissions: the sum of oxides of nitrogen (NOx) in the flue gas, collectively 

expressed as nitrogen dioxide. 

3.13 Process Heater: any combustion equipment fired on gaseous or liquid fuel, which 

transfers heat from combustion gases to water or process streams. Process heaters 

exclude kilns or ovens used for drying, baking, cooking, calcining, heat treating, 

or vitrifying. 

3.14 PUC Quality Natural Gas: California Public Utility Commission Quality Natural 

Gas is any gaseous fuel, gas-containing fuel where the sulfur content is no more 

than one-fourth (0.25) grain of hydrogen sulfide per one hundred (100) standard 

cubic feet and no more than five (5) grains of total sulfur per one hundred (100) 

standard cubic feet. PUC quality natural gas also means high methane gas of at 

least 80% methane by volume. 

3.15 3.14 Rated Heat Input: the heat input capacity, usually expressed as million Btu per 

hour (MMBtu/hr), usually specified on the nameplate of the unit. If the unit has 

been physically modified such that its maximum heat input differs from what is 

specified on the nameplate, the modified maximum heat input shall be considered 

as the rated heat input and made enforceable by Permit to Operate or Registration 

Certificate. 
PROPOSED November 14, 2013 

4308 - 3 Proposed Amendments to Rule 4308 

3.16 3.15 Recreational Vehicle: any vehicle used for recreational purposes and designed 

to include a water heater and is required to be licensed to be driven or moved on 

the highways of California. 

3.17 SCAQMD: South Coast Air Quality Management District. 

3.18 3.16 Unit: any boiler, process heater, or water heater as defined in this rule. 

4.0 Exemptions 

The provisions of this rule shall not apply to: 

4.1 Units installed in manufactured homes, and; 

4.2 Units installed in recreational vehicles.; and 

4.3 Hot water pressure washers. 

5.0 Requirements 

5.1 Until December 31, 20142010, a person shall not supply, sell, offer for sale, 

install or solicit the installation of any boiler, process heater or water heater 

unless it has been certified pursuant to Section 6.1 and complies with Table 1, 

Tier 1 NOx limits and CO limits specified in Section 5.3. 

5.2 On, and after January 1, 2015,2011 a person shall not supply, sell, offer for 

sale, install or solicit the installation of any boiler, process heater or water 

heater unless it has been certified pursuant to Section 6.1 and complies with 

Table 21, Tier 2 NOx limits and CO limits specified in Section 5.3. 

5.3 Units with a rated heat input capacity of 400,000 Btu per hour 0.4 MMBtu/hr to 

less than 2,000,000 Btu per hour 2.0 MMBtu/hr shall not exceed the CO limit 

of 400 ppm at 3% stack gas oxygen by volume on a dry basis. 
PROPOSED November 14, 2013 

4308 - 4 Proposed Amendments to Rule 4308 

Table 1 

Emissions Limits (Effective until December 31, 2014) 

Type and Size of Unit, 

in MMBtu/hr

NOx Limit 

(at 3% stack gas oxygen by volume on a dry basis) 

All Fuels PUC Gas Non PUC Gas or 

Liquid 

Tier 1 

lb/MMBtu of heat 

input (ppmv) 

Tier 2 

lb/MMBtu of heat 

input (ppmv) 

Tier 2 

lb/MMBtu of heat 

input (ppmv) 

Units greater than or equal to 0.075 

but less than or equal to 0.4, except 

as specified below 

0.093 (77) 0.024 (20) 0.093 (77) 

Units greater than 0.4 but less than 

2.0, except as specified below 0.036 (30) 0.024 (20) 0.036 (30) 

Instantaneous water heaters and pool 

heaters greater than or equal to 

0.075 but less than or equal to 0.4 

0.093 (77) 0.068 (55) 0.093 (77) 

Instantaneous water heaters and pool 

heaters greater than 0.4 but less than 

2.0 

0.036 (30) 0.024 (20) 0.036 (30) 

Table 2 

Emission Limits (Effective on and after January 1, 2015) 

Type and Size of Unit, 

in MMBtu/hr

NOx Limit 

(at 3% stack gas oxygen by volume on a dry basis) 

PUC Gas Non PUC Gas or 

Liquid 

lb/MMBtu of heat input 

(ppmv) 

lb/MMBtu of heat input 

(ppmv) 

Units greater than or equal to 0.075 but less 

than or equal to 0.4, except as specified below 0.024 (20) 0.093 (77) 

Units greater than 0.4 but less than 2.0, 

except as specified below 0.024 (20) 0.036 (30) 

Instantaneous water heaters greater than or 

equal to 0.075 but less than or equal to 0.4 0.024 (20) 0.093 (77) 

Instantaneous water heaters greater than 

0.4 but less than 2.0 0.024 (20) 0.036 (30) 

Pool heaters greater than or equal to 0.075 but 

less than or equal to 0.4 0.068 (55) 0.093 (77) 

Pool heaters greater than 0.4 but less than 2.0 0.024 (20) 0.036 (30) 
PROPOSED November 14, 2013 

4308 - 5 Proposed Amendments to Rule 4308 

6.0 Administrative Requirements 

6.1 Methods of Emission Certification 

 6.1.1 Certified emissions levels shall be demonstrated by an emission certification 

approved under either of the following: 

6.1.1 6.1.1.1 The District’s certification program as described in Section 6.2 and 

6.3 of this rule. 

6.1.2 6.1.1.2 The South Coast Air Quality Management District (SCAQMD) 

Certification List for Rule 1146.2. Units certified pursuant to Rule 1146.2 

must comply with applicable emission limits pursuant to District Rule 4308 

Table 1 and the compliance schedule in Section 7.0.

6.1.3 6.1.1.3 Other emission certification programs approved by the EPA and 

APCO. 

6.2 District Certification Program Specifications – Unit Manufacturer 

6.2.1 For each new unit or retrofit kit to be certified, the manufacturer shall 

obtain from an independent testing laboratory, a certification source test 

verifying compliance with the emission limits in Section 5.0. The results 

should shall be submitted with the compliance report information in 

Section 6.3. 

6.2.2 Source tests shall be conducted on a randomly selected unit no more than 

90 days prior to the date of proposed certification of the model by the 

District. 

6.2.3 Tests shall be conducted and reports shall be prepared according to 

District Rule 1081 (Source Sampling) and, for natural gas-fired units, the 

“Nitrogen Oxides Emissions Compliance Testing for Natural Gas-Fired 

Water Heaters and Small Boilers,” Protocol, South Coast Air Quality 

Management District SCAQMD, Source Testing and Engineering 

Branch, Applied Science and Technology. 

6.2.4 District certification for a manufacturer shall be valid for three years 

from the date of certification. 

6.2.5 The District shall publish and maintain a list of certified emissions for 

the tested unit. 
PROPOSED November 14, 2013 

4308 - 6 Proposed Amendments to Rule 4308 

6.3 Compliance Report 

The compliance report shall be submitted to the District and shall contain the 

following information: 

6.3.1. Name and address of manufacturer, 

6.3.2 Brand name, 

6.3.3 Model number, as it appears on the permanent nameplate, and 

6.3.4 Description of the model unit or retrofit kit being certified, 

including burner type and rated heat input capacity. 

6.3.5 A report on the certification test specified in Section 6.2.3. 

6.3.6 A signed and dated statement attesting, under penalty of perjury, 

to the accuracy of all statements and information in the 

compliance report. 

 

 6.4 Identification of Compliant Units 

 

 The manufacturer subject to Section 6.2 shall display the model number and the 

certification status, as determined in Section 6.2 of this rule, of an applicable 

unit or retrofit kit on the permanent nameplate of the unit or kit. If packaging 

obscures the permanent nameplate, the model number and certification status 

shall also appear on the packaging. 

7.0 Compliance Schedule 

7.1 Until December 31, 2010, a person shall comply with the requirements of Section 

5.1 and Section 5.3 

7.2 On and after January 1, 2011, a person shall comply with the requirements of 

Section 5.2 and Section 5.3.