SCAQMD-Certified Boilers and Water Heaters:
What the Approved Equipment List Means for Your Building
If you manage a commercial building in Southern California and your water heater or boiler is due for replacement, the most important thing to know before you buy anything is this:
South Coast AQMD maintains an official list of certified units, and only equipment certified under Rule 1146.2 is permitted for installation in the AQMD jurisdiction, with that list serving as the public record of what has been certified.
Choosing the wrong unit, even one marketed as energy-efficient or low-emission, can put your building out of compliance on the day it is installed.
This article explains what the certified list is, how equipment gets on it, how to read it, and what it means for the decisions you make when replacing equipment in your building.
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What the Certified List Is
The SCAQMD Certified Units List is the official database of water heaters, boilers, and process heaters that have been tested and confirmed to meet the NOx emission limits established under Rule 1146.2. The list is maintained by the South Coast Air Quality Management District and is published on the AQMD website. As of this writing, the most recent update was December 30, 2025.
The list exists because SCAQMD Rule 1146.2 requires that any unit manufactured, sold, or installed for use within the South Coast AQMD must be certified by the AQMD Executive Officer. Certification is not self-reported by manufacturers. It requires testing by an independent laboratory and review by AQMD staff before a unit is added to the list.
If a unit has not been certified under Rule 1146.2, it cannot legally be installed in the jurisdiction, regardless of what the manufacturer claims about its emissions performance. In practice, that means checking the current certified list.
What Certification Actually Involves
Getting a unit onto the certified list is not a simple paperwork exercise. The certification process under Rule 1146.2 works as follows.
First, the manufacturer must obtain confirmation from an Independent Testing Laboratory that each unit model complies with the applicable Table 1 emission limits when fired with natural gas.
The testing laboratory must meet the requirements of AQMD Rule 304 and must be approved by the AQMD Executive Officer to conduct certification testing under the official Protocol for Nitrogen Oxides Emissions Compliance Testing for Natural Gas-Fired Water Heaters and Small Boilers.
Table 1
| Equipment Category | NOx Emission Limit | CO Emission Limit |
|---|---|---|
| Type 1 Units, excluding Pool Heaters | 14 ng/J or 20 ppmv | N/A |
| Type 1 Pool Heaters | 40 ng/J or 55 ppmv | N/A |
| Type 2 Units | 14 ng/J or 20 ppmv | 400 ppmv |
The source test involves measuring actual NOx emissions from a randomly selected unit of each model under controlled conditions. The results are documented in a source test report that includes the unit’s NOx and CO emissions, the model and serial number tested, the Rated Heat Input Capacity, and the name of the independent laboratory that conducted the test.
The manufacturer then submits the certification application to the AQMD Executive Officer within 180 days of the source test date. The application includes a signed statement of compliance, general information about the manufacturer and unit, a description of the model being certified, and the source test report.
Only after the Executive Officer reviews and approves the application is the unit added to the certified list.
This process means that every unit on the list has been physically tested by an independent laboratory and reviewed by AQMD staff. It is not a self-certification scheme.
Type 1 vs. Type 2 Units
The certified list distinguishes between two equipment categories based on size, and understanding this distinction matters when you are selecting replacement equipment.
Type 1 Units
Type 1 units have a Rated Heat Input Capacity of 400,000 BTU per hour or less. This covers most commercial water heaters found in smaller multifamily buildings, restaurants, retail spaces, and mid-sized office buildings. Type 1 units must meet a NOx emission limit of 14 ng/J or 20 ppm.
Type 2 Units
Type 2 units have a Rated Heat Input Capacity above 400,000 BTU/hr up to and including 2,000,000 BTU/hr (2 MMBtu/hr). These are the larger commercial units found in hotels, hospitals, larger apartment complexes, and commercial facilities with higher hot water demand.
Type 2 units must meet the same 14 ng/J or 20 ppm NOx limit, along with a carbon monoxide (CO) limit of 400 ppm.
Pool heaters are a separate subcategory under Type 1 with a higher allowable NOx limit of 40 ng/J or 55 ppm, reflecting the different combustion characteristics of pool heating equipment.
When you are looking at the certified list, make sure the unit you are considering is certified in the correct category for your equipment’s size. A unit certified as Type 1 cannot be used as a replacement for Type 2 equipment.
Who Is on the List
The certified list includes units from a wide range of manufacturers. Among the brands commonly found in commercial and multifamily settings in Southern California are Aerco International, Advanced Thermal Hydronics (Mestek), Bradford White, A.O. Smith, Lochinvar, Navien, Noritz, Rheem, and Rinnai, among many others.
The list covers both storage-type and instantaneous (tankless) water heaters, as well as small boilers used for hydronic heating and domestic hot water applications.
We are not endorsing any specific manufacturer. What the list tells you is that these products have cleared the certification process and can legally be installed in the AQMD jurisdiction. The right choice for your building depends on your load requirements, available space, fuel infrastructure, and budget, all of which vary significantly from one facility to the next.
If you want to verify whether a specific model is currently certified, always check the AQMD website directly for the current version of the list. Models can be added or removed as manufacturers update their product lines or let certifications lapse.
What Happens When a Certified Model Is Discontinued
This is a situation that comes up more often than people expect. Manufacturers periodically discontinue models, update product lines, or rebrand equipment. When a certified model is discontinued, it is eventually removed from the certified list, and replacement units of the same model may no longer be available.
If you are planning a replacement and the model currently installed in your building is no longer on the certified list, you cannot simply order the same unit. You will need to select a currently certified equivalent. This is worth knowing before you are in an emergency situation with a failed unit and a 72-hour compliance notification deadline approaching.
For larger facilities with multiple units, this is one of the reasons that working with a contractor who tracks the certified list regularly is valuable. Porter Boiler’s SCAQMD compliance services include advising clients on certified equipment selection as part of the replacement planning process, not just at the point of installation.
Why Certified Equipment Still Requires Expert Installation
Being on the certified list means a unit has passed emissions testing under controlled laboratory conditions. It does not guarantee correct installation or AQMD compliance on its own. Several things can go wrong if installation is handled by someone unfamiliar with the requirements.
Rule 1146.2 specifies that the installer must hold a valid California Contractors State License Board license for a classification related to buildings and appliances. After installation, the building owner or operator is required to report to AQMD through the Compliance Portal within 72 hours. This notification must include the date the unit was installed, the model and serial number, and confirmation that the unit meets the applicable emission limits.
Beyond the reporting requirement, proper installation affects whether the unit actually performs at the certified emission levels in the field. Incorrect combustion air setup, improper gas pressure, or inadequate venting can cause a certified unit to operate outside its tested parameters, creating a compliance problem even with an approved unit.
This is why commercial water heater installation and boiler work require a contractor who understands AQMD requirements and compliance obligations.
There are also recordkeeping obligations that attach to the building owner after installation. You are required to maintain a copy of the manufacturer or distributor instructions, a record of maintenance activity for at least three years, and documentation of the unit’s Rated Heat Input Capacity.
If you are using one of the alternative compliance options under Rule 1146.2, such as the utility upgrade extension or the leased property extension, additional records must be kept and available for AQMD inspection.
For more detail on what alternative compliance options are available if you cannot meet your deadline, see our article on your options if you cannot meet the SCAQMD Rule 1146.2 deadline.
How to Use the Certified List When Planning a Replacement
When you are approaching a replacement decision, here is the practical sequence to follow:
- Start by confirming your unit’s Rated Heat Input Capacity from the manufacturer’s rating plate. This determines whether you need a Type 1 or Type 2 certified unit. Then confirm your building type and equipment category to understand which compliance phase and deadline apply to you.
- Once you know the category you need, check the current certified list on the AQMD website. Do not rely on a list you downloaded previously. The list is updated regularly and the version on the AQMD website is the authoritative one.
- From there, work with your contractor to evaluate which certified units are appropriate for your building’s load requirements, space constraints, and infrastructure. In some cases, transitioning from a natural gas unit to an electric or heat pump unit will require electrical panel upgrades, additional circuits, or physical space modifications. These are real project considerations that need to be factored into your timeline before your compliance date arrives.
Where Porter Boiler Fits In
Porter Boiler Service installs certified equipment across Los Angeles, Long Beach, Orange County, and the surrounding Southern California area.
We are familiar with the certified list, follow its updates, and have been navigating AQMD permitting and installation requirements in Southern California for over 65 years.
If you need help identifying which certified unit is right for your building or understanding what compliance requires for your specific situation, we are available to help.