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What is an A2L? A guide to the switch from HFC to HFO

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What is an A2L?

A2L is a refrigerant safety classification assigned by (American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).  ASHRAE Standard 34 assigns an identifying reference letter and number to each refrigerant, which classifies the refrigerant according to the hazard involved in its use.  The capital letter (A) designates a toxicity class.  Refrigerants assigned an A have lower toxicity, while refrigerants assigned a B have higher toxicity. 

The second and third digits of the ASHRAE safety classification (2L) represent the flammability classification of the refrigerant as assigned by ASHRAE Standard 34.  There are three ASHRAE flammability classifications and one subclass.  Those classifications are 1 (no flame propagation), 2 (lower flammability), and 3 (higher flammability).  The subclass is 2L, mildly flammable.

An A2L refrigerant has a lower toxicity and has a low burning velocity.  While an A2L does show a small amount more flame propagation than an A1 refrigerant, it shows substantially less than an A3 refrigerant. 

Forane® R-32, a replacement for R410A, is an A2L.

Read more about working safely with A2Ls.

What do you mean when you talk about “Flammability”?

It is a reference to ASHRAE Standard 34 flammability classifications, which take into account flammability limits, burning velocities, and other flammability properties of refrigerants.  
A1 refrigerants, including R-410A and R-22, will burn under the right conditions.  However, when tested according to ASHRAE’s  test methodology for flammable refrigerants, R-410A shows no flame propagation whereas R-32 and R-454B does.  Read more about flammability here.

What are the safety classification assigned by ASHRAE for flammability?

ASHRAE has three flammability classifications and one subclass for refrigerants:

  1. 1= No flame propagation refrigerants.  Some HFC’s and some HFO’s fall into this category including: Forane® R-22, Forane® R-134a, Forane® R-410A, and Forane® HTS 1233ZD.
  2. 2L = Mildly flammable refrigerants. Some HFC’s, and some HFO’s fall into this category including: Forane® R-32, R-1234yf and Forane® R-516A.
  3. 2 = Lower Flammability. Some HFC’s like R-152a are class 2.
  4. 3= Higher flammability. Hydrocarbons such as propane, Iso Butane, R-600, etc., would be considered class 3.

Are all refrigerants tested for flammability under ASHRAE Standard 34

All refrigerants are tested for flammability, and toxicity under ASHRAE Standard 34

Why do we need A2Ls? Why are we moving from HFCs to HFOs?

Historically, the refrigerants industry has used A1, or no flame propagation refrigerants. With the issuance of the EPA’s Allowance Allocation Rule and the October 2021 petition, a limit has been placed on refrigerants with a Global Warming Potential (GWP) over 700 for gases used in new residential and light commercial air conditioners as of 01/01/2025.

In order to meet these GWP requirements, the industry is moving to A2Ls, like Forane® R-32, because of their superior efficiency and lower GWP. Forane® R-32 has a GWP of 675 as well as higher capacity and better efficiency over R-410A.

To learn more about the replacement for R-410A, check out the benefits of R-32 over R-410A.


Our A2Ls FAQ guide covers everything from the basics, to cylinder changes, and the AIM Act. 

Download The Guide