A2L building codes and state adoption

Which model codes cover A2Ls

There are two families of model mechanical codes in the US. Most jurisdictions use the International Codes (I-Codes) from the ICC; some use the Uniform Mechanical Code (UMC) from IAPMO. A2L provisions are in the 2024 editions of both.

I-Codes. The ICC’s Building Safety Journal (January 26, 2022) reported that code changes approved in the 2021 Group A cycle “go into effect with the 2024 IBC, IFC and IMC, permit the use of A2L refrigerants for human comfort uses,” consistent with ASHRAE 15-2019 and UL 60335-2-40. The ICC’s 2024 A2L change document collects the changes to the IFC, IBC, IRC and IMC in one place.

UMC. In the 2024 UMC, Table 1102.3 lists refrigerant groups, properties and allowable quantities, including the A2L blends. IAPMO issued TIA 003-24 to correct that table. ASHRAE, the submitter, wrote that the table was updated from ASHRAE 34-2019 and its addenda, which “contained errors” in the RCLs and LFLs of A2L blends. The TIA revises the rows for blends including R-454A, R-454B and R-454C. If your jurisdiction uses the UMC, ask whether it adopted the 2024 edition with the TIA.

What the 2024 IRC requires

For one- and two-family dwellings, the A2L text sits in IRC Section M1411. From the ICC’s required changes to the 2021 IRC:

The referenced standards are ASHRAE 34-2022 and UL/CSA 60335-2-40 (2022 edition). Because M1411.2 and M1411.6 point back to the listing, the manufacturer’s room area table becomes a code requirement; see A2L charge limits.

What the 2024 IMC requires

For commercial work, the 2024 change document shows these IMC Chapter 11 provisions, among others:

• 1101.2.1: high-probability equipment using A2L, A2, A3 or B1 refrigerant must comply with UL 484, UL/CSA 60335-2-40 or UL/CSA 60335-2-89.
• 1104.3.1: high-probability systems for human comfort must use Group A1 or A2L refrigerant.
• Table 1103.1: reclassifies refrigerants such as R-32 to A2L and lists RCL and LFL values.
• 1106.4: A2L and B2L machinery rooms: no open-flame devices or continuously operating hot surfaces over 1,290°F (700°C), detectors and emergency ventilation. Details are on the refrigerant detection systems page.
• 1109.2.7 and 1109.3: pipe identification with “WARNING – Risk of Fire. Flammable Refrigerant.” for A2L, shield plates in framing, and ventilated pipe shafts.
• 1110.3: test gases: oxygen-free nitrogen, helium, argon or a nonflammable tracer mix; never oxygen, air or combustible gases.

Field practices under these sections are on installing and servicing A2L systems.

Jurisdictions on older editions

For jurisdictions still on an older edition, the ICC published documents showing the edits needed to bring older editions in line with the 2024 A2L text:

• Required Changes to the 2018 IMC (first published December 13, 2022; this version March 1, 2023).
• Required Changes to the 2021 IRC (June 14, 2024).

Each document says: “Jurisdictions that desire to adopt into legislation the provisions of this publication may do so through incorporation by reference.” So a jurisdiction can stay on the 2018 or 2021 code and still allow A2Ls by adopting the ICC amendment.

How states make it legal

There are two routes, and the AHRI map tracks both. AHRI describes the map as showing “where state and local building codes have been updated or legislation passed to allow equipment using A2L refrigerants.”

• Code adoption. The state or local code body adopts the 2024 code, or an older code plus the ICC A2L amendments, through its normal rulemaking.
• Legislation. A statute directs or allows A2L use, sometimes ahead of a full code update.

The standards themselves are not law. ASHRAE’s special note in its standards says: “Compliance with this Standard is voluntary until and unless a legal jurisdiction makes compliance mandatory through legislation.” ASHRAE 15, 15.2 and UL 60335-2-40 apply on a job because a code, a statute or the listing pulls them in.

The map is a snapshot, not a legal record. AHRI says it “will be revised as building codes and legislation are updated” and the page shows no last-updated date. The last count we could verify is from HARDI, citing AHRI, on February 15, 2024: “Today, A2Ls can be used in 44 states.” Do not treat that as current. This page lists no states because we could not verify each one against a primary source dated in 2026.

Federal rules are a separate layer. EPA decides which refrigerants are allowed in new equipment (SNAP and the Technology Transitions GWP limits); building codes decide how they are installed. See AIM Act refrigerant rules.

What to check with the local authority

Before the first A2L install in a jurisdiction, ask the building department:

1. Which mechanical or residential code edition is in force, and whether it includes A2L provisions (2024 edition, or an older edition with the ICC required changes or a state amendment).
2. Any local amendments to Section M1411 (IRC), Chapter 11 (IMC or UMC), or the referenced standard editions.
3. For UMC jurisdictions, whether TIA 003-24 is adopted.
4. What the inspector wants at final: the installation manual left on site (IRC M1411.3), the completed charge label (M1411.5), the room area check against the manufacturer’s table, and pressure test results (M1411.7).
5. Permit scope for a changeout: whether reusing a line set or keeping an existing coil is allowed. Manufacturers such as Rheem already require an approved coil and recommend replacing the line set.
6. Fire code issues for commercial work: machinery room detection, emergency ventilation and hazardous-location rules (IFC 608 and IMC 1106).

Keep the answer in writing with the date. Codes and amendments change, and the AHRI map can lag a local decision.