IRC 2024 Mechanical Equipment Listing: UL, ETL, and AGA Certification Requirements

Quick Answer

Yes. IRC 2024 Section M1301.2 requires that all mechanical equipment and appliances regulated by the code be listed and labeled by an approved testing laboratory. Common approved laboratories include UL (Underwriters Laboratories), ETL (Intertek), CSA Group, AGA (American Gas Association), and AHRI (Air-Conditioning, Heating, and Refrigeration Institute).

Under IRC 2024, equipment must be installed in strict accordance with its listing and the manufacturer’s installation instructions, which are considered part of the code requirements for that piece of equipment.

What IRC 2024 Actually Requires

Section M1301.2 establishes two parallel requirements: the equipment must be listed, and it must be labeled. Listing means the equipment has been evaluated and approved by a nationally recognized testing laboratory (NRTL) accredited by OSHA. Labeling means the approval is affixed to the equipment in a permanent, visible manner, typically as a metal tag or embossed plate on the unit itself.

The IRC intentionally does not repeat the detailed installation requirements found in the equipment’s listing and manufacturer instructions. Instead, it incorporates those requirements by reference. This means a contractor who ignores the manufacturer’s installation manual is not merely violating a manufacturer recommendation — they are violating the building code itself. The installation instructions are legally binding once the equipment is installed in a jurisdiction that has adopted IRC 2024.

For gas appliances, AGA and CSA certification covers the gas train and combustion components. UL listing typically covers electrical safety. Many pieces of equipment carry multiple certifications. An inspector may check for the presence of multiple listing marks on high-BTU gas equipment, verifying that both the gas and electrical components have been tested.

Used equipment must also be listed. IRC 2024 does not prohibit the installation of used mechanical equipment, but it does require that any installed equipment bear a valid listing mark from an approved laboratory. Equipment that has had its listing mark removed, that has been modified from its listed configuration, or that was manufactured before listing requirements existed in that product category is prohibited.

Why This Rule Exists

The listing requirement exists because the IRC cannot anticipate every possible failure mode of every piece of mechanical equipment. Rather than attempting to prescribe detailed construction standards for hundreds of appliance types, the code defers to the specialized testing laboratories that have developed product-specific standards over decades. A UL-listed furnace has been tested against ANSI Z21.47, which specifies hundreds of safety tests including flame rollout, heat exchanger integrity, and pressure relief. The IRC simply requires that furnaces be listed — and in doing so, incorporates all of those tests by reference.

The alternative — installing unlisted equipment — means the occupants are living with a device that has never been evaluated for residential safety. No third party has confirmed that the heat exchanger won’t crack under thermal cycling, that the gas valve fails safely, or that the electrical controls meet residential safety standards.

The IRC 2024 approach reflects the same philosophy as its predecessors: the code sets the performance standard (“be listed”), and the testing labs set the technical criteria (“pass 500 tests per ANSI Z21.47”). This two-layer system keeps the code compact while ensuring rigorous equipment-level safety testing. The shift from IRC 2021 to IRC 2024 did not fundamentally change M1301.2, but it updated cross-references to several equipment standards that were themselves revised to reflect newer product categories, particularly variable-capacity heat pumps and modulating furnaces.

What the Inspector Checks at Rough and Final

At the time of equipment installation, inspectors look for the listing mark on the nameplate or data plate of every major piece of mechanical equipment. For furnaces and air handlers, this is typically found on the interior of the cabinet. For condensing units, it is on the exterior nameplate. For water heaters, it is on the outer jacket label.

Inspectors also verify that the installation matches the listing requirements by reviewing the installation manual, which contractors are expected to have on-site. Common installation-specific checks include confirming that clearances to combustibles match the nameplate requirements, that the gas supply pressure is within the listed range (typically 7 inches water column for natural gas), and that the electrical supply voltage and ampacity match the equipment’s listed specifications.

What Contractors Need to Know

Contractors must source equipment from authorized distributors to ensure listing integrity. Gray-market equipment — units imported outside of authorized distribution channels — may appear similar to listed models but may lack the listing, use substandard components, or be configured for different fuel types or voltages than what the listing specifies.

When installing equipment, keep the installation manual on-site for the inspector. Many experienced inspectors will ask to review it, particularly for unfamiliar brands or new product categories. If the manual is lost, download and print it before the inspection. An inspector who cannot verify that the installation matches the listing requirements has grounds to fail the inspection.

Contractors should also understand that field modifications to listed equipment can void the listing. Adding a non-listed pressure switch to a listed furnace, for example, removes the equipment from its listed configuration. Any modification must be either within the scope of the original listing or must use a listed accessory specifically approved for use with that equipment.

What Homeowners Get Wrong

Homeowners sometimes purchase mechanical equipment online from overseas sources at significant discounts. These units are rarely listed by an approved NRTL, and their installation will be rejected by any AHJ following IRC 2024. Even if the equipment appears functional, it cannot be legally installed in a permitted project.

A related issue arises when homeowners purchase used equipment from a commercial building — for example, a lightly-used rooftop unit. Commercial equipment may be listed, but it may be listed to different standards than residential equipment. Residential jurisdictions frequently require equipment listed to residential standards (ANSI Z21-series for gas, UL residential series for electrical). An inspector may reject commercially-listed equipment in a residential application even if it carries a UL mark, if that mark is for a commercial product standard rather than a residential one.

A third error is assuming that a piece of equipment sold at a major home improvement retailer is automatically listed for residential use. Most major-brand equipment sold through authorized channels is properly listed, but “open box” or return units may have had listing labels removed during return processing. Inspect the nameplate before accepting any unit, and refuse any unit that does not display a clear, undamaged NRTL listing mark appropriate to the product category.

State and Local Amendments

California requires that HVAC equipment meet both the listing requirement of IRC M1301.2 and the efficiency standards of Title 24. Equipment that is listed but does not meet the applicable SEER2 or AFUE minimums cannot be installed in California regardless of listing status. This means the listing is necessary but not sufficient in California — efficiency compliance is an additional requirement layered on top.

Some local jurisdictions maintain lists of approved equipment or approved manufacturers as a supplement to the NRTL listing requirement. If your AHJ has such a list, verify that your intended equipment appears on it before purchasing.

When to Hire a Professional

The listing and labeling verification process is something a professional contractor handles as a matter of routine. For homeowners who are evaluating contractor bids, the key action is to ask for the equipment make and model before accepting the bid, then verify independently that the equipment is listed. You can search for listed products on the UL Product iQ database, the CSA certified products listing, or the AHRI directory.

If you are ever presented with a bid that includes equipment you cannot find in any listing database, treat it as a red flag. Either the equipment is unlisted (a code violation) or it is being sourced from an unauthorized channel. Neither outcome is acceptable for a permitted mechanical installation.

For specialized equipment categories — such as variable-refrigerant-flow (VRF) systems, geothermal heat pumps, or absorption chillers — the listing verification process is more nuanced. Some of these systems carry listings from laboratories that are NRTL-accredited for specific product categories only. A listing that is valid for commercial applications may not extend to residential use, even if the laboratory name is the same. A licensed mechanical engineer or a contractor specializing in that equipment category is best positioned to verify that the specific listing applies to the residential jurisdiction in question.

Common Violations Found at Inspection

• Equipment installed without a visible listing mark, often because the nameplate label was damaged during shipping or installation
• Gray-market or overseas-sourced equipment that carries a CE mark (European standard) but no NRTL listing valid in the United States
• Field modifications to listed equipment, such as adding non-listed components or altering the gas train, that void the original listing
• Installation manual absent from the job site, preventing the inspector from verifying that listing-specific requirements were followed
• Used commercial equipment installed in a residential application where the listing standard does not apply to residential use
• Equipment substituted from the permitted model without updating the permit, resulting in an unlisted unit being installed under a permit issued for a listed model
• Refrigerant type or charge amount not matching the listing, often found when technicians substitute refrigerants without verifying compatibility with the equipment’s listed configuration