A2L refrigerants guide

What A2L means

The safety group has two parts. The letter is toxicity: A means lower toxicity (occupational exposure limit of 400 ppm or more), B means higher toxicity (below 400 ppm). The number is flammability: 1 (no flame propagation), 2L, 2 and 3.

Under Addendum g to ASHRAE 34-2016, a single-compound refrigerant is Class 2L when it shows flame propagation at 140°F (60°C) and 14.7 psia, has an LFL above 0.0062 lb/ft³ (0.10 kg/m³), has a heat of combustion below 8,169 Btu/lb (19,000 kJ/kg), and has a maximum burning velocity of 3.9 in/s (10 cm/s) or less. Before that addendum, 2L was an optional subclass of Class 2; Addendum g made it a separate class.

In practice: an A2L will burn if a leak reaches a flammable concentration and meets an ignition source, but it is much harder to ignite and burns far more slowly than propane (A3). The full criteria and the blend rules are on the flammability safety classes page.

Which refrigerants are A2L

Classes below are from Table 1103.1 in the ICC 2024 I-Code A2L change document, which reclassifies these from A2 to A2L. GWP is the IPCC AR4 100-year value, the basis EPA uses under the AIM Act.

Ammonia (R-717) is also a 2L, but it is B2L because of its toxicity. R-410A, R-22 and R-134a are A1.

None of these is a drop-in for an existing system. Rheem’s R-454B installation instructions say R-454B “cannot be retrofitted into R-410A and R-22 heat pumps,” and that R-410A or R-22 indoor coils have not been evaluated for R-454B and “may lack a refrigerant detection system necessary for safe operation.” The R-410A vs R-454B comparison covers the field differences.

What changes for techs

Tools and service equipment

Carrier’s 50FE R-454B instructions say it plainly: “All service equipment or components must be A2L refrigerant rated. Do not use non-A2L rated equipment or components on R-454B refrigerant equipment.” Rheem says to verify that service equipment and instruments are certified for use with group A2L refrigerants, and in particular with R-454B.

Rheem’s tool list for R-454B models: manifold sets rated to 800 psig high side and 250 psig low side (550 psig low-side retard), hoses with an 800 psig service pressure rating, and recovery cylinders rated 400 psig (DOT 4BA400 or 4BW400). Recovery machines must be certified for flammable refrigerants; see recovery machine compatibility.

Brazing and ignition sources

Rheem’s A2L service section requires checking the area with a suitable refrigerant detector before and during work, keeping ignition sources away, having a dry powder or CO2 extinguisher at hand for hot work, and making sure the area is open or ventilated before breaking into the system. Nitrogen must be flowing while brazing.

If a leak needs brazing, Rheem says all refrigerant must be recovered, or isolated with shutoff valves away from the leak, and the circuit purged with oxygen-free nitrogen. Compressed air or oxygen must not be used for purging, and the vacuum pump exhaust must not be near an ignition source.

Leak detection

Rheem: “A halide torch (or any other detector using a naked flame) shall NOT be used.” Electronic detectors are allowed if they are not an ignition source and suit the refrigerant; they must be set at a percentage of the refrigerant’s LFL (25% maximum) and calibrated in a refrigerant-free area. Bubble and fluorescent methods are acceptable, but avoid detergents containing chlorine. Rheem also asks that field-made line-set joints be leak tested with an A2L-compatible detector with a sensitivity of 0.2 oz/year (5 g/year) or better.

Refrigerant detection systems in the equipment

Above a charge-to-room-area threshold, the equipment needs a refrigerant detection system that runs the blower on a leak. Rheem’s charge table marks where a leak detection sensor becomes required; Carrier’s 50FE ships with a sensor and a dissipation board. Details are on the refrigerant detection systems page.

Labeling and cylinders

Under IRC M1411.5 in the ICC required changes to the 2021 IRC, each A2L system must carry a manufacturer-supplied label marked with the installing company’s contact information, the system charge and the refrigerant number.

R-454B cylinders are light green-gray with a red band on the shoulder or top to show flammability (Rheem). Rheem also lists the cylinder fittings: CGA 164 for R-454B cylinders under 50 lb and CGA 670 for cylinders over 50 lb. See refrigerant cylinder colors.

Charging and charge limits

Rheem says R-454B must be charged as liquid, with the cylinder inverted. Under IRC M1411.6 (2024 A2L text), the charge must follow the manufacturer’s instructions and the listing, and the A2L charge for an individual refrigeration system “shall not exceed 34.5 pounds (15.7 kg).” For target pressures, use the bubble and dew columns in the PT calculator, never a single-column chart.

Codes and where A2Ls are allowed

The 2024 I-Codes carry the A2L provisions. In the ICC’s required changes to the 2021 IRC:

• M1411.2: A2L systems must be listed and labeled to UL/CSA 60335-2-40 and installed per the listing.
• M1411.3: install per the manufacturer’s instructions, then leave the manuals attached to the indoor unit or with the homeowner.
• M1411.4: field-installed accessories go in per the accessory and equipment manufacturers’ instructions, and accessories installed in the ductwork of A2L systems must not contain electric heating elements, open flames, or devices switching electrical loads greater than 2.5 kVA.
• M1411.7: A2L piping is tested per the manufacturer’s instructions and the listing.

The referenced standards are ASHRAE 34-2022 and UL/CSA 60335-2-40 (2022 edition). For commercial work, IMC 1104.3.1 in the same ICC document says high-probability systems used for human comfort must use Group A1 or A2L refrigerant.

State and local adoption varies. In February 2024, HARDI, citing AHRI, reported that A2Ls could be used in 44 states. Check AHRI’s building code map and the local building official for the current status.

Why the switch happened

Under 40 CFR 84.54, new residential and light commercial AC and heat pump systems using refrigerants with a GWP of 700 or more cannot be installed from January 1, 2025, unless all specified components were made or imported before that date. R-410A (GWP 2,088) is over the limit; R-32 and R-454B are under it. Existing R-410A equipment can still be serviced. See AIM Act refrigerant rules and R-410A phase-out.