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    A2L refrigerants: what they are, the list, the rules and the certification question

    An A2L refrigerant sits in ASHRAE Standard 34 safety group A2L: no toxicity identified at or below 400 ppm (the "A") and lower flammability (the "2L"). It can burn, but it burns slowly. R-32, R-454B and R-1234yf are all A2L, and EPA allows A2Ls in residential and light commercial AC only in new equipment built to UL 60335-2-40, 3rd edition.

    Every fact below comes from EPA, the Federal Register, the eCFR, OSHA or BLS, checked Sept 24, 2026, unless we name another source (AHRI's cylinder guideline; ACHR News and ESCO on the 2026 bank). Where EPA only advises, we say so.

    What is an A2L refrigerant?

    EPA describes ASHRAE 34 this way: "The initial capital letter indicates the toxicity, and the numeral denotes the flammability" (88 FR 26386, Apr 28, 2023).

    CodeWhat it means, as EPA describes ASHRAE 34
    AToxicity not identified at or below 400 ppm by volume
    BEvidence of toxicity below 400 ppm by volume
    1No flame propagation when tested
    2LFlame propagation, heat of combustion under 19,000 kJ/kg, LFL above 0.10 kg/m³, and a maximum burning velocity of 10 cm/s or lower
    2Same as 2L without the burning-velocity limit
    3Heat of combustion of 19,000 kJ/kg or more, or LFL of 0.10 kg/m³ or less

    Three takeaways:

    • Lower is not zero. EPA calls 2L "lower flammability", lower than classes 2 and 3 (86 FR 24458, May 6, 2021). OSHA's June 6, 2024 letter is blunter: "These refrigerants are flammable."
    • Blends are rated on their worst case of formulation and fractionation (88 FR 26386).
    • Letter and number are separate. R-123 is B1: evidence of toxicity, no flame propagation.

    Why A2Ls are showing up now

    EPA's Technology Transitions rule (88 FR 73098, Oct 24, 2023; 40 CFR 84.54) sets a GWP limit of 700 for new residential and light commercial AC and heat pump systems. EPA's SNAP table lists R-410A at about 2,090, R-32 at 675 and R-454B at 470. Systems using a refrigerant with a GWP of 700 or more may still be installed where all specified components were made or imported before Jan 1, 2025 (final rule 91 FR 31284, effective July 27, 2026).

    A2L refrigerant list, with EPA classes and GWPs

    These are the A2Ls EPA names in its SNAP rules and tables, not every refrigerant ASHRAE has classed A2L.

    RefrigerantWhat it isSafety groupGWP as EPA lists it
    R-32 (HFC-32)Single HFC (difluoromethane)A2L675
    R-454BBlend: 68.9% R-32, 31.1% R-1234yfA2L470
    R-452BBlendA2L700
    R-454ABlendA2L240
    R-454CBlendA2L150
    R-457ABlendA2L140
    R-1234yfHFOA2LUnder 5
    R-1234ze(E)HFOA2LUnder 10
    R-455A, R-516ABlendsA2LNot in the EPA tables we checked

    Blend GWPs are EPA's "about" figures from SNAP Rule 23 (IPCC AR4, 100-year). EPA's documents give R-1234yf as "less than four", "one" and "4", and R-1234ze(E) as 6 or 1, so we give a ceiling instead of picking one.

    For comparison, common non-A2L refrigerants:

    RefrigerantSafety groupGWP as EPA lists it
    R-410AA1About 2,090
    R-134aA11,430
    R-744 (CO₂)A11
    R-123B177
    R-290 (propane)A33
    R-600a (isobutane)A33
    R-441AA3Under 5

    A2L refrigerant regulations: EPA's SNAP rules

    EPA's SNAP program lists acceptable refrigerants one end use at a time. For A2Ls, each listing comes with binding "use conditions".

    • SNAP Rule 23 (86 FR 24444, May 6, 2021; effective June 7, 2021): R-32, R-452B, R-454A, R-454B, R-454C and R-457A in new residential and light commercial AC and heat pumps. Codified as Appendix W to 40 CFR 82 subpart G.
    • SNAP Rule 25 (88 FR 26382, Apr 28, 2023; effective May 30, 2023): comfort-cooling chillers and residential dehumidifiers, including R-1234yf. Chillers must also meet ASHRAE 15-2019.
    • SNAP Rule 26 (89 FR 50410, June 13, 2024; effective July 15, 2024): retail food refrigeration, commercial ice machines, industrial process refrigeration, cold storage and ice rinks.

    A2L refrigerant requirements for residential and light commercial AC

    From Appendix W (eCFR current to Aug 19, 2026) and the 2021 rule:

    • New equipment only. No retrofits. "New" means "a completely new refrigeration circuit containing a new compressor, evaporator, and condenser"; existing tubing "can be inspected and if suitable re-used".
    • UL 60335-2-40, 3rd edition. EPA proposed moving to the 4th edition (90 FR 50766, Nov 10, 2025); no final rule as of Sept 24, 2026. EPA's SNAP Q&A (updated Aug 31, 2026) allows 4th-edition equipment only if it also meets Edition 3, charge sizes included.
    • Charge set by room size, per UL 60335-2-40.
    • Warning labels. Permanent, in letters at least 1/4 inch (6.4 mm) high; EPA chose that over UL's 1/8 inch. The outside label reads: "WARNING—Risk of Fire. Flammable Refrigerant Used. To Be Repaired Only By Trained Service Personnel. Do Not Puncture Refrigerant Tubing."
    • Red service ports. Ports, pipes and hoses marked red (PMS #185 or RAL 3020), at least 1 inch in both directions, replaced if removed.
    • Detection. "In certain applications", factory-installed refrigerant detection triggers mitigation such as fan operation or ventilation.
    • Ductwork. On fixed equipment, no auxiliary devices that may be ignition sources in the ductwork unless listed for that appliance.

    "New equipment only" doesn't stop service work. EPA wrote in 2023 that the use condition "does not affect the ability to service a system using the refrigerant once installed, including the adding of refrigerant or replacing components."

    Venting and penalties

    A2Ls are not exempt substitutes. EPA's 2021 rule says knowingly venting them during service, repair or disposal "is prohibited" (CAA section 608(c)(2); 40 CFR 82.154(a)(1)). The Clean Air Act civil penalty maximum is $124,426 per day per violation (40 CFR 19.4, penalties assessed on or after Jan 8, 2025).

    A2L technician safety: what EPA advises

    Know which parts are rules and which are advice. EPA's SNAP listings carry a "further information" column that EPA says is "not binding for the use of the substitutes under the SNAP program", though it "may be binding under other regulatory programs (e.g., worker protection regulations promulgated by OSHA)".

    In that column, EPA advises:

    • Use only spark-proof tools on equipment with flammable refrigerants.
    • Use recovery equipment designed for flammable refrigerants.
    • Only technicians specifically trained in handling flammable refrigerants should service it, with training consistent with Annex HH of UL 60335-2-40, 3rd edition. EPA notes Annex HH itself is informative, not required.
    • If refrigerant in the air rises above one-fourth of the lower flammability limit (LFL), evacuate the space; re-enter only after it has been ventilated.
    • Keep a class B dry powder fire extinguisher nearby; wear chemical goggles and protective gloves.

    These come from regulations, not the advice column:

    • Recovery equipment for flammable refrigerants made or imported after Jan 1, 2017 is certified under Appendix B4 to subpart F, based on AHRI 740-2016 and UL 1963 Supplement SB (40 CFR 82.158).
    • Flammable refrigerant recovered from residential and light commercial AC is "likely to be hazardous waste" under RCRA (86 FR 24457). Lower-flammability spent refrigerant recycled for reuse can follow 40 CFR 266 subpart Q (89 FR 82871, Oct 11, 2024).

    Cylinders. AHRI Guideline N-2017 says refrigerant containers "should" be light green-gray (RAL 7044), with a red band on the shoulder or top for flammables, and that colors shouldn't be relied on alone. EPA cites the Guideline N red band in its 2021 rule. It is an industry guideline: we found no federal rule requiring the red band, or left-hand threads, on stationary cylinders.

    Not on EPA's pages: brazing precautions for A2Ls, leak-detector types, or a stand-alone A2L servicing guide.

    This is what EPA's listings say, not training. Get hands-on A2L training from your employer, school or equipment maker before you open a flammable system.

    Is there an A2L certification?

    No federal one. We checked EPA, OSHA, DOE and BLS on Sept 24, 2026 and found no federal A2L certification or training requirement. When EPA listed the first A2Ls for home AC in 2021, it said "training is best left to the industry" (86 FR 24468–24469).

    What the law requires is Section 608 certification. 40 CFR 82.161(a) requires it for anyone who could open the refrigerant circuit on appliances containing a class I or class II refrigerant "or a non-exempt substitute refrigerant". R-32, R-454B and the other A2Ls are non-exempt substitutes, covered since Jan 1, 2018.

    The Type follows the equipment: Type I for small appliances (factory-sealed, 5 lb or less), Type II for medium-, high- and very high-pressure appliances, Type III for low-pressure ones. EPA's rule names no A2L in its pressure-class examples; our reading routes A2L equipment that isn't a small appliance to Type II, and Universal covers all three. More in EPA 608 certification and the Type II guide.

    Some programs and trade groups sell their own A2L courses and certificates. Under federal rules those are voluntary: nothing we found requires one on top of 608. ACHR News also reports the revised 608 exam will not add a separate A2L certification type.

    State and local rules can add more. EPA said in 2021 that where building codes apply, "other authorities would be responsible for ensuring such requirements are addressed and enforced." BLS tells HVAC techs to check with their state and locality.

    A3 refrigerants (hydrocarbons) in brief

    R-290 (propane), R-600a (isobutane) and R-441A are A3, the highest flammability class. Their SNAP listings cap the charge:

    • Household refrigerators and freezers: UL 60335-2-24, at most 150 g (5.29 oz) per circuit. The old 57 g limit was removed effective Sept 7, 2018 (83 FR 38969).
    • Stand-alone retail units on R-290: SNAP Rule 26 replaced UL 471's 150 g with UL 60335-2-89: roughly 500 g open, roughly 300 g with doors and drawers.
    • Vending machines: 150 g (5.29 oz) per circuit.
    • Self-contained room AC: never more than 1,000 g of propane or R-441A; portable units 300 g of propane or 330 g of R-441A.

    Propane, isobutane and R-441A are exempt from the venting prohibition, and from subpart F's requirements, only in the end uses listed in 40 CFR 82.154(a)(1), such as household refrigerators and vending machines. A2Ls get no such exemption. And EPA bans R-22a and all class 3 refrigerants as retrofits in residential and light commercial split AC (SNAP Rule 21; EPA R-22a Q&A, updated Mar 3, 2026).

    How A2Ls connect to the EPA 608 exam

    A2L questions are not a 2026 invention. In 2021 EPA wrote that "EPA's 608 test bank already includes questions concerning A2L refrigerants and the appliances covered by this rule" (86 FR 24468).

    The 2026 part is reported, not published by EPA. ESCO Institute's homepage offers both a "2018" and a "2026" EPA exam. ACHR News reported on Sept 19, 2026, quoting ESCO, "the addition of general knowledge questions on A2L and A3 refrigerants", and that old-bank exams "can be administered only through Jan. 1, 2027". EPA has not posted the change as of Sept 24, 2026. The fair reading: expanded A2L/A3 coverage, reported. Details in the 2026 EPA 608 question bank.

    Who does what: EPA writes the rules and releases its question bank "only to approved technician certification programs". The 87 approved programs (EPA list, Aug 20, 2026) give the test and issue the card. Pass608 is an independent study tool; our A2L/A3 set is 40 original questions written from the rules on this page.

    Try 10 A2L/A3 questions free — free account, no card.

    A2L refrigerant FAQ

    Is R-410A an A2L refrigerant?

    No. EPA's SNAP table lists R-410A as A1 (no flame propagation), with a GWP of about 2,090.

    Can I put R-32 or R-454B in an R-410A system?

    No. EPA's listing allows these A2Ls "only in new equipment designed to address concerns unique to flammable refrigerants", not as a retrofit refrigerant.

    Do I need a separate A2L certification?

    Not under federal rules as of Sept 24, 2026. You need Section 608 certification at the Type that fits the equipment. Program A2L certificates are voluntary.

    Can I service an existing A2L system?

    Yes, with the right 608 certification. EPA says the new-equipment condition doesn't affect servicing an installed system.

    Is R-1234yf an A2L refrigerant?

    Yes. In stationary equipment, 608 rules apply. In car AC it falls under Section 609, a different credential.

    Sources

    Checked Sept 24, 2026 unless noted.