Boilers and Process Heaters

Boilers and process heaters emit air contaminants including oxides of nitrogen, carbon monoxide, volatile organic compounds, oxides of sulfur, particulate matter and toxic air contaminants. All boilers and process heaters with a maximum heat input equal to or greater than 5 million Btu per hour (MMBtu/hr) require a permit to operate from the District. In addition, units capable of being fired on liquid fuel with a maximum heat input rating equal to or greater than 1 MMBtu/hr require a permit to operate.

Beginning April 1, 2021, the District will begin accepting applications for boilers above 2 MMBtu/hr and less than 5 MMBtu/hr. These “medium size” boilers will require registration or permitting, even if fired exclusively on gaseous fuels. For registering these 2 to 5 MMBtu/hr boilers, see our registration page.

Boilers can operate on a variety of fuels including natural gas, propane or fuel oil. Boilers can be used to produce hot water or steam. Process heaters are used to heat a working fluid other than water where flue gas does not come into contact with the working fluid. Common techniques for controlling emissions include the use of low NOx burners, flue gas recirculation, other combustion modifications, or exhaust aftertreatment with a process such as selective catalytic reduction (SCR).

The information on this page will assist in the completion and submittal of an application for each boiler and process heater. Each section of the page contains important information needed to submit an application.

Need to register a boiler between 2 and 5 MMBtu/hr? See our registration page.

Application forms tell us about your operation and enable us to permit your process. Accurate and complete information decreases processing time and helps avoid additional charges for unnecessary revisions. Please carefully review and complete the following forms. Also listed below are required attachments that must be submitted with each application. For most boilers, you will complete the standard supplemental form. For low-use or temporary boilers (under 220,000 therms per year or under 10% capacity) using natural gas or propane, please complete the low-use/temporary boiler supplemental form only. Low-use/temporary boiler applications may also be submitted online.

General Application: Word PDF

Standard Boiler Supplemental Form Word PDF

Low-Use/Temporary Boiler Supplemental Form Word PDF

Required Attachments:

  • Plot Plan including stack location and nearby building dimensions
  • Manufacturer supplied emission data or source test results
  • Boiler specification/data sheet
  • Control equipment specifications (if applicable)
  • BACT analysis (if applicable)

The general and equipment specific application forms along with all required attachments must be submitted with each application packet.

The correct fee must be submitted with your application in order for it to be accepted. For this type of equipment, depending on the application type, the fees are either listed in the table(s) below or are determined based on the time and materials required to conduct the review. If your application type is not listed in the table(s), a fee estimate must be obtained from the District prior to submittal. Please note that the fees listed in these tables are estimated and the final fee may be more or less than this amount based on time and materials spent processing the application. The District maintains work records for this purpose.

Fee Tables

Boilers < 50 MMBtu/hr heat input, annual fuel use 220,000 therms or less
Boilers < 50 MMBtu/hr heat input, annual fuel use greater than 220,000 therms
Boilers > 2MMBtu/hr and < 5 MMBtu/hr (natural gas and liquid fuel)

Before submitting an application, contact the District (see Assistance tab) to obtain an application fee estimate for application submittal. Please note that an additional fee may also apply depending on the method of payment. A breakdown of how the application fee(s) are determined can be seen here. Additional information can be found in District Rule 40.

How to Pay

These fees may be paid by check payable to "Air Pollution Control District" or by credit card (Visa, MasterCard, Discover, and American Express).

If you choose to email or fax your application and intend on paying with a credit card, ensure that you have obtained your fee estimate and have it in hand, and then after submitting the application, you must contact the District over the phone at (858)586-2600 to provide payment information.

Please note that credit card payments are assessed a transaction fee of 2.19% that is charged by the credit card provider.

Citizen Access
Select equipment type applications can now be submitted online.

Fax: (858) 586-2601

Permit Processing
10124 Old Grove Rd
San Diego, CA 92131-1649

The District will act on complete applications as soon as possible but at most within 180 days. The engineer assigned to your application will review it and contact you within 30 days of receipt to confirm that it is complete or request additional information. Typically permits are issued in about 60 days. More complex processes will take longer. Common reasons that applications may take longer than 60 days to evaluate include: the project is a complex project specifically at a major source, if the project requires a mandatory public notice period due to being installed within 1000 feet of a school or triggering the requirement for a air quality impact analysis (AQIA), if they do not initially pass a health risk assessment (HRA) or AQIA, if BACT is not proposed or complete BACT analysis is not submitted or for major sources if actual emission data is not included.

Ensuring your application is complete is the best way to reduce processing time. Complete emissions data is the most important factor in minimizing application processing time and iterative information requests. If you have any questions about what information is required, please contact the District using the information on the Assistance tab.

Sign up for Citizen Access to get up to date information on the status of your application.

Learn more about the permitting process and what to expect.

Best Available Control Technology

If a piece of equipment or a process emits more than 10 pounds per day of particulate matter (PM10), oxides of nitrogen (NOx), volatile organic compounds (VOC) or oxides of sulfur (SOx), the application must include a best available control technology (BACT) analysis.  Boilers can trigger BACT requirements for any of these pollutants depending on size and fuel type.  The District has a BACT guide to assist with the analysis. If you have questions or need assistance reference the contact information at the bottom of this page. Please review District Rules 20.1 and 20.2.


District Rule 1200 applies to any new, relocated, or modified emission unit which may increase emissions of one or more toxic air contaminant(s). The proposed project must comply with Rule 1200. Proposed equipment may require toxics best available control technology (TBACT) depending on the project. Please review District Rule 1200 for further details.

Trade Secret

District rules address how information that is submitted to the District is managed. District Regulation IX contains District Rules 176 and 177. Please refer directly to these rules when submitting trade secret information. However, be aware that you will need to submit:

  1. You must indicate on the general application form that your submittal includes trade secret information to ensure that it is not inadvertently made publicly available.
  2. A letter disclosing the proprietary information. Ideally, this information should be separated from your application and clearly identifiable. This can be submitted electronically, and can be a separate submittal from the main application package.
  3. A letter for the  public record explaining why the information needs to be held as trade secret or is otherwise exempt from disclosure.

Applications submitted with incomplete material composition data due to failure to include proprietary information can significantly delay permit applications. In an effort to expedite the permit application process it is recommended that you contact the manufacturer or vendor of any proprietary materials that are used in the process and prepare the required letters as part of your application submittal.


In 1989, the California state legislature passed a law, AB 3205, designed to protect schoolchildren from hazardous air contaminants. The law, as currently written, requires the District to notify parents of schoolchildren, neighboring businesses and residents of all new or modified equipment that emits any hazardous air contaminant into the air which will be installed within 1,000 feet of a school site. The law also requires the District to consider any comments before authorizing construction. Please review your proposed location. If a school property boundary is located within 1,000 feet of the proposed emissions point, the AB3205 process will be initiated. This process requires a 30 day public comment period and the overall process will delay projects by at least six weeks.


Depending on the installation date, stationary source emissions, and fuel type the following federal New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAP) may be applicable to your boiler.

Major source Boiler NESHAP (subpart DDDDD) - Applies to boilers that will be located at major sources of HAP emissions.

Area source Boiler NESHAP (subpart JJJJJJ) - Does not apply to boilers fired only on natural gas or with liquid fuel only for emergencies.

Boiler NSPS - Separate rules for boilers between 10 MMBtu/hr and 100 MMBtu/hr (subpart Dc) and boilers greater than 100 MMBtu/hr that are not utility boilers (subpart Db). The rules contain emission standards for NOx, PM and SOx for some boilers; however, subpart Dc does not have any NOx emission standards. Additional requirements include monitoring and recordkeeping requirements. Most boilers fired on only natural gas or fuel oil meet the requirements of this rule by using low sulfur containing fuels and keeping fuel records.

Utility Boiler Rules - Boilers used to produce steam that is fed to a steam turbine used to produce grid electricity are subject to additional rules include NSPS subpart Da and may be subject to others.

The engineer assigned to an application will review the proposed equipment to determine the requirements of these regulations that may apply and include them as conditions in your authority to construct..

District Rules

Several District rules may apply to your equipment. General rules that may apply to boilers include Rules 505152, 5354, and 62.

Equipment specific Rules 69 and 69.2 apply to boilers and process heaters. However rule 69 applies only to electric utility boilers. Rule 69.2 contains emission standards for NOx, testing, monitoring and other operational requirements. Depending on size and annual heat input, the rule requires either annual testing or annual tuneups among other requirements. A complete listing of the District's rules can be found here.

Calculation Procedures and Additional Resources

Equipment Calculation Procedures - This page contains procedures to be used for calculating emissions from this equipment that should be submitted with each application.

Use of these calculation procedures will aid in minimizing application review time and costs.  The correct emission factors should be selected from the list based on equipment. If available, manufacturer provided equipment specific emission data or source test results should be utilized before using default emission factors. Sources of all emission data used must be included as attachments to the application.

AP-42 - An alternative compilation of emission factors and calculation procedures prepared by the EPA that may be utilized by the District in some situations for some equipment types.

Call Duty Engineer
(858) 586-2600

District Small Business Assistance Program Coordinator
(858) 586-2656