What A2L means
ASHRAE Standard 34 gives every refrigerant a safety group of a letter and a number. The letter is toxicity: class A refrigerants have an occupational exposure limit of 400 ppm or more, class B less. The number is flammability, based on flame tests at 140°F (60°C) and 73.4°F (23°C) at atmospheric pressure:
| Class | Meaning | Examples |
|---|---|---|
| 1 | No flame propagation in the test | R-22, R-134a, R-410A, R-407C, R-404A (all A1) |
| 2L | Lower flammability: propagates flame, but lower flammable limit above 0.10 kg/m3, heat of combustion below 19,000 kJ/kg, and maximum burning velocity of 10 cm/s (3.9 in/s) or less | R-32, R-454B, R-452B, R-454A, R-1234yf, R-1234ze(E) (all A2L) |
| 2 | Flammable, burning velocity above 10 cm/s | R-152a |
| 3 | Higher flammability: lower flammable limit below 0.10 kg/m3 or heat of combustion above 19,000 kJ/kg | R-290 propane (A3) |
Class 2L became its own classification through an addendum to Standard 34-2016. An ASHRAE and UN Environment factsheet sums it up as class 2 refrigerants "that burn very slowly". Slow is not never: A2L refrigerants are flammable, and every safety rule for them follows from that.
Common A2L refrigerants
- R-454B and R-32: the two main contenders to replace R-410A, per Arkema. EPA's Technology Transitions reference table lists their GWPs as 465 and 675.
- R-452B: listed by EPA for new residential and light-commercial AC and heat pumps.
- R-1234yf: used in the majority of light-duty vehicles, per EPA, and a component of R-454B.
They are showing up because EPA's Technology Transitions rule limits refrigerants in new residential and light-commercial AC and heat pump systems to a GWP below 700, and limits new light-duty vehicles to below 150. EPA's SNAP program lists R-454B, R-452B and R-32 as acceptable in that equipment subject to use conditions, including that the equipment meets UL 60335-2-40, 3rd edition. Comparisons: R-410A vs R-454B, R-454B vs R-32, R-134a vs R-1234yf.
Equipment standards, briefly
These summaries are for orientation only. The standards themselves, the equipment's installation instructions and the codes adopted where you work are what apply.
- UL 60335-2-40 is the safety standard for AC and heat pump equipment. UL Solutions' summary of the 3rd edition (November 2019) says that above a charge limit, typically more than 4 lb, systems need refrigerant leak detectors that sense a leak in the occupied space, activate below 25% of the lower flammable limit, and start the indoor fan to dilute the refrigerant. UL Standards and Engagement published a 4th edition in December 2022, and UL Solutions says its updated detection requirements became mandatory for new certifications from January 1, 2025.
- ASHRAE 15 covers the safe design, construction, installation and operation of refrigeration systems. ASHRAE 15.2 was written to accommodate A2L refrigerants in residential applications.
- Codes. AHRI notes that flammable refrigerants may be used only in systems designed and listed for them, and only where the applicable codes and standards or the authority having jurisdiction (AHJ) allow. Check with the local AHJ.
What changes for techs
- Tools. AHRI's A2L best practices call for an A2L-rated vacuum pump and recovery tools rated for A2L refrigerants. UL 1963 covers recovery and recycling equipment for flammable refrigerants through its Supplement SB. Chemours lists 2L-certified electronic leak detectors and recovery machines, and vacuum pumps with the switch located away from the work zone.
- Cylinders. AHRI Guideline N has called for every refrigerant container to be light green-gray (RAL 7044) since 2020, with a red band on the shoulder or top for flammable refrigerants. Arkema notes that A2L cylinders use a left-hand thread on the valve outlet (CGA 166 instead of CGA 165) to prevent cross-contamination with A1 refrigerants, and a reclosing pressure relief device instead of a rupture disc.
- Jobsite. AHRI's checklist starts with reading the SDS and the equipment manual, ventilating the area and checking for ignition sources and flammable vapors. It also calls for nitrogen during brazing, recovering all refrigerant before opening a system, and never venting.
- Charging. AHRI says a 400-series blend such as R-454B must leave the cylinder as liquid; Arkema says single-component R-32 can be charged as vapor or liquid. Do not exceed the maximum charge in the equipment instructions, and record the charge on the unit label as UL 60335-2-40 requires, per AHRI.
- Leak detection. AHRI notes that the detectors and sensors in UL 60335-2-40 are control systems inside the equipment, not alarms for occupants. The handheld detector you carry is separate; AHRI's task force calls for leak detectors rated for A2L refrigerants.
- Labels. Manufacturer instructions add steps such as labeling decommissioned equipment and making sure flammability labels stay on the unit.
Never retrofit an A2L into A1 equipment
A2L refrigerants go only into equipment designed and listed for them. Copeland states that A2L refrigerants should not be retrofitted into non-A2L compressors or products, and Arkema notes that R-410A systems lack the safety features A2L refrigerants require. EPA's SNAP listings for R-454B and R-32 cover new equipment only.
Where to read the rules
- EPA SNAP listings for residential and light-commercial AC and heat pumps
- UL Solutions summary of UL 60335-2-40
- ASHRAE refrigeration resources (Standards 15, 15.2 and 34)
- AHRI Safe Refrigerant Transition Task Force
EPA's refrigerant sales restriction still applies: with limited exceptions, only technicians certified under Section 608 or Section 609 may buy ozone-depleting or substitute refrigerants. Anyone who services car AC for payment or barter must be certified under Section 609.