A2L Rules Vary City to City Because Codes Adopt Safety Standards Edition by Edition

Under the 2024 International Mechanical Code (IMC), A2L piping that passes through two or more floor/ceiling assemblies belongs in a ventilated, fire-rated shaft, with listed exceptions, Jim Cika of the International Code Council (ICC) wrote in April 2025. Oregon building officials must now approve an alternate that drops the shaft for continuous, tested pipe if the applicant chooses it. Seattle accepts the same alternate through a code modification request prepared by a registered design professional. New York City exempts a room from the dispersal calculation only when the pipe runs inside a same-material outer sleeve and 2-hour construction.

All four answers trace to a few national documents, read at different editions and amended differently. ASHRAE 15, 15.2 and 34, UL 60335-2-40 and the printed IMC, IRC and UMC are sold publications, and their full text was not reviewed here. This account relies on ASHRAE's free addenda, ICC and IAPMO change documents, state and city rules, and engineering articles, each named where it is used. The unit's installation manual and the authority having jurisdiction (AHJ) govern any job.

From Voluntary Standard to Enforceable Code

ASHRAE's addenda each carry the same sentence: "Compliance with this Standard is voluntary until and unless a legal jurisdiction makes compliance mandatory through legislation." ASHRAE 34 supplies the safety group, lower flammability limit (LFL) and refrigerant concentration limit (RCL). ASHRAE 15 sets charge, mitigation and piping requirements, and 15.2 does the same for listed systems serving a single dwelling or sleeping unit. UL/CSA 60335-2-40 is the product listing, and Cika says the listing obliges manufacturers to put instructions for the charge calculations in the manual.

The model codes reference those documents: ICC's IMC and IRC, and IAPMO's Uniform Mechanical Code (UMC), which ACHR News described in 2022 as used by states including California, Nevada, New Mexico and Texas. A published edition has no legal effect until a state or locality adopts it, Cika told ACHR News, and a jurisdiction can also write selected provisions into an older code. EPA runs on a separate track. Its SNAP Rule 23 ties R-32 and R-454B to the Nov. 1, 2019, edition of UL 60335-2-40, while the 2024 IMC points to the 2022 edition.

R-454B's Flammability Limit Went Into the Books Wrong

Model codes copy refrigerant properties into their own tables, and some of the 2024 copies were wrong. Both the IMC's Table 1103.1 and the UMC's Table 1102.3 carried an R-454B LFL of 22.0 pounds per 1,000 cubic feet. ASHRAE's corrections set it at 18.5 and moved the RCL from 3.1 to 4.6. In a February 2025 filing, ASHRAE told ICC that inflated values "may lead to Code Officials erroneously approving larger refrigerant charge sizes" than ASHRAE 15 and UL/CSA 60335-2-40 would allow. That filing says IAPMO issued its fix, TIA 003-24, on Nov. 6, 2024. A 2026 letter from HARDI and AHRI says ICC followed with Interim Critical Amendment TSG-000001.

Small Rooms and Zone Dampers Under 15.2

Addendum c to 15.2, approved March 29, 2024, decides how much floor counts. A ducted system without a leak detection system is held to the smallest room on its supply ductwork. With detection or continuous circulation, the aggregate floor area on that ductwork counts, although spaces "where the airflow may be limited by zone dampers" drop out for continuous-circulation systems. The same addendum requires zoning dampers to open within 15 seconds of the detector's signal.

At a 7.2-foot dispersal height, Addendum a's Table 9-3 gives an allowable amount M of 6.9 pounds at 100 square feet with or without circulation. At 200 square feet it gives 13.8 pounds with circulation and 11.9 without, and at 500 square feet, 34.4 and 18.8. Addendum a also struck the old circulation multiplier AF from the charge formula, leaving maximum charge equal to a conversion factor C times M, with any ventilation allowance added to M, and Addendum c carries the same formula. Addendum c lowered R-454B's C from 0.97 to 0.96, and the later Addendum f prints 0.96. The consolidated 2024 edition was not reviewed, so no worked charge figure appears here.

Trane's Steve Kujak wrote in Contracting Business that, under ASHRAE 15, units above 4 pounds "must ship with factory-installed refrigerant detectors." Addendum c to 15.2 strikes that standard's older rule requiring an integral detector above the m1 level, along with its exceptions. In their place it requires a leak detection system above m1 releasable charge when that system starts the circulation or ventilation used to comply, and on any system using safety shut-off valves to comply. The same addendum requires installation in accordance with the listing, which can settle the question for a given unit.

ICC's change document for the 2021 IRC caps Group A2L charge at 34.5 pounds per system. Addendum f's m2 charge levels, 35.0 pounds for R-32 and 33.9 for R-454B, fall on either side of that figure. The ICC document also bars field-installed ductwork accessories with electric heating elements, open flames or devices switching more than 2.5 kVA, while Addendum c contemplates electric duct heaters and requires them de-energized on a leak signal unless airflow is proven and exceeds 200 feet per minute.

Apartments Change the Standard and the Math

A multifamily job first has to settle which standard applies. Washington's State Building Code Council, answering Bellevue in Opinion 24-18, accepted 15.2-2022 compliance with AHJ approval, required the whole system to follow either 15 or 15.2, and, again on AHJ approval, let jointless piping for several single-unit systems share an unvented rated shaft. New York City's Section 7015-03 confines 15.2 to one- and two-family dwellings in Group R3, which leaves an apartment tower's systems outside it.

Variable refrigerant flow adds a charge spread across many rooms. Writing in HPAC Engineering on Sept. 30, Tarang Patel of TRV Mechanical Contractors described a circuit feeding a 90-square-foot bedroom and a 400-square-foot great room. The bedroom's limit, he wrote, governs "applied against the full system charge" until detection and mitigation come into play. His remedies include splitting circuits by room size, shortening pipe runs and giving small bedrooms their own circuit or a non-VRF terminal. Patel cites no edition or section of any code, so the piece reads as a designer's account of practice.

Manufacturer-side guidance starts further along, at releasable charge. A Havtech article built on a presentation by Daikin's Chris Bellshaw works a 112-square-foot room with an 8.5-foot ceiling: just over 9 pounds allowed, against about 2.78 pounds releasable at the indoor unit branch with long piping (refrigerant unnamed). New York's rule prints the same test, releasable charge at or below the effective dispersal volume charge (EDVC). Addendum f to 15.2 shows the same logic on the residential side: without safety shut-off valves, releasable charge equals system charge, and with them it covers what sits downstream. Trane's Joseph Guerin wrote in HPAC that VRF without detection and valves can satisfy ASHRAE 15 on projects "very few and far between." Daikin and Trane both sell VRF.

Guerin says ASHRAE Interpretation IC 15-2022-12 treats a branch controller as separate from pipe, so it needs its own dispersal calculation, and Seattle says a refrigerant controller is "not simply refrigerant pipe or tube." Havtech says a corridor ceiling plenum can become the evaluated space, while Patel lists corridors among spaces that "tolerate higher charge limits than bedrooms." New York allows corridor piping only with the sleeve and 2-hour enclosure, and ICC's change document bars piping exposed in a fire-rated exit access corridor. "The industry may not agree with the current interpretation, but it's the way the standard is written, and that is how teams have to design today," Bellshaw said.

Shaft Language Outran the Code Books

Addendum b to ASHRAE 15-2024 says piping "shall be permitted" in a rated shaft and makes sealed penetrations the primary protection. Its foreword says the model building codes dropped a mandatory shaft in the 1980s, which sits awkwardly beside the "shall be enclosed" wording of Section 1109.2.5 as Oregon reprints it. The addendum also waives shaft ventilation for continuous, tested pipe, and for A2L or B2L systems with tested pipe and joints and no surface above 1,290 degrees F in the shaft. Guerin's September 2025 statement that any A2L shaft must be ventilated predates that change.

Addendum b also reprints a shaft detector set point no higher than the occupational exposure limit, which IAPMO's table lists as 850 ppm for R-454B. ICC's change document for the IMC, Section 1109.3.2, says 25 percent of LFL, roughly 28,750 ppm using the 115,000 ppm LFL in ASHRAE's filing. Washington was still amending its 2021 IMC by emergency rule in December 2025, coordinating it with the latest standards while permanent rulemaking continued.

Checking a Jurisdiction

AHRI's A2L Building Code Map is the common starting point. A tally of its 50 state pages and D.C. on Nov. 4 found air conditioning codes marked updated in 18, allowed by state law in 27, allowed by letter of interpretation in four (Idaho, Kentucky, Michigan and Nevada), and not updated in Alaska and D.C. For ASHRAE 15, it lists pre-2019 editions in 26, 2019 in 11, 2022 in 14 and 2024 in none. The HARDI and AHRI letter says "Many states and jurisdictions are adopting ASHRAE 15-2024," so either the map lags its own publisher or those adoptions are still in progress. Oregon's entry still shows 2022 despite the December alternate.

Texas appears as allowed under SB 1210 with pre-2019 standards and separate links for Austin and Houston, and Guerin reports that the North Central Texas Council of Governments approved regional amendments to the 2024 IMC using ASHRAE 15-2022 wording. Where the adopted code lags, the route is often an alternative-method approval. North Carolina's State Fire Marshal laid out three paths under its 2018 code in June 2024, called the prescriptive one "very restrictive" and said that anyone using ASHRAE 15 as the alternative must comply with "the full standard," not selected provisions.

A 2022 ACHR News report described the 2024 IMC as limiting A2L systems to 6.6 pounds in residential and 22 pounds in commercial use. ICC's March 2023 change document prints those figures as exceptions to the rule that high-probability comfort systems use Group A1 or A2L refrigerant, which reads as room for small listed equipment using other groups. The printed 2024 IMC should settle that reading, and Cika says allowable quantities rest on ASHRAE 15 calculations.

Sources

1. ASHRAE, Addendum a to ANSI/ASHRAE Standard 15.2-2022, approved Oct. 31, 2022. ashrae.org
2. ASHRAE, Addendum c to ANSI/ASHRAE Standard 15.2-2022, approved March 29, 2024. ashrae.org
3. ASHRAE, Addendum f to ANSI/ASHRAE Standard 15.2-2022, approved July 31, 2024. ashrae.org
4. ASHRAE, Addendum e to ANSI/ASHRAE Standard 15.2-2024. ashrae.org
5. ASHRAE, Addendum b to ANSI/ASHRAE Standard 15-2024, approved March 31, 2026. ashrae.org
6. ICC, "Required Changes to the 2021 International Mechanical Code," March 1, 2023. iccsafe.org
7. ICC, "Required Changes to the 2021 International Residential Code," June 14, 2024. iccsafe.org
8. Emily Toto for ASHRAE, ICC Interim Critical Amendment request on 2024 IMC Table 1103.1, Feb. 19, 2025. iccsafe.org
9. IAPMO, UMC TIA 003-24, 2024 UMC Table 1102.3. iapmo.org
10. Jim Cika, ICC Building Safety Journal, "A2L Refrigerants: Latest Challenges and Opportunities," April 28, 2025. iccsafe.org
11. Jim Cika, ICC Building Safety Journal, "Insights on the HVAC Industry Transition to A2L Refrigerants," July 28, 2026. iccsafe.org
12. Jim Cika, ACHR News, "The Code Challenges Behind the A2L Transition," Aug. 22, 2025. achrnews.com
13. Joanna R. Turpin, ACHR News, "Finalizing the A2L Provisions in 2024 Mechanical Codes," Oct. 6, 2022. achrnews.com
14. AHRI, A2L Refrigerant Building Code Map, state pages read Nov. 4, 2026. ahrinet.org
15. Oregon Building Codes Division, Statewide Alternate Method No. 25-01, Dec. 11, 2025. oregon.gov
16. Seattle SDCI, Construction Code Interpretation, 2021 SMC Section 1109.2.5, Aug. 4, 2025. seattle.gov
17. Washington State Building Code Council, State Building Code Opinion No. 24-18. sbcc.wa.gov
18. Washington State Building Code Council, emergency rule WSR 26-01-075, filed Dec. 12, 2025. leg.wa.gov
19. New York City Department of Buildings, 1 RCNY 7011-01, A2L Refrigerating Systems. nyc.gov
20. New York City Department of Buildings, 1 RCNY 7015-03, ASHRAE 15.2 amendment. nyc.gov
21. HARDI and AHRI, joint letter to the New York City Department of Buildings on the Local Law 77 A2L rule, 2026. refindustry.com
22. North Carolina Office of the State Fire Marshal, guidance paper on A2L systems under the 2018 NC Mechanical Code, June 4, 2024. ncosfm.gov
23. California Department of Housing and Community Development, addendum to initial statement of reasons, 2022 California Mechanical Code. dgs.ca.gov
24. California Office of the State Fire Marshal, SFM 01/24 commission action matrix, 2025 California Mechanical Code. dgs.ca.gov
25. California Office of the State Fire Marshal, SFM 02/25 initial statement of reasons. dgs.ca.gov
26. California Business Properties Association and others, Industry Coalition letter of support, April 24, 2026. dgs.ca.gov
27. Tarang Patel, HPAC Engineering, "Engineering A2L Compliance Into Multifamily VRF Systems," Sept. 30, 2026. hpac.com
28. Joseph Guerin, HPAC Engineering, "VRF and A2L Refrigerants: What Engineers Need to Know," Sept. 17, 2025. hpac.com
29. Tim Dorman with Chris Bellshaw, Havtech, "How A2L Refrigerants Change VRF Design in Hotels and Multifamily Buildings." havtech.com
30. Steve Kujak, Contracting Business, "ASHRAE Standard 15 Offers Contractors Guidance and Flexibility When Working with A2L Refrigerants," Sept. 10, 2025. contractingbusiness.com
31. EPA, SNAP Rule 23 final rule, 86 FR 24444, May 6, 2021. govinfo.gov
32. EPA, "Phasedown of Hydrofluorocarbons: Reconsideration of Certain Regulatory Requirements," final rule, 91 FR 31284, May 26, 2026. federalregister.gov