Updated refrigerant designations

The April 2026 fact sheet provides an update on ASHRAE standards for refrigerants, and introduces the new refrigerants that have been awarded an “R”.

ASHRAE standard 34, Designation and Safety Classification of Refrigerants, establishes a common system for referring to refrigerants. It uses assigned numbers rather than chemical names, formulas or trade names; which are based on toxicity and flammability.

Refrigerants are numbered with an “R”, followed by the assigned number. As the fact sheet explains, isomers (a molecule with the same chemical formula as another molecule but with a different chemical structure) are identified with a lower case letter after the number (for example, R-134a). Refrigerant blends having the same pure components but with different compositions are identified with an upper case letter after the number (for example, R-401A and R-401B or R-4101A and R-4101B).

Refrigerants having the form R-4xxx or R-4xxxx are zeotropic (blends of two or more refrigerants whose liquid phase and vapor phase always have different composition), while those with the form R-5xxx are azeotropes (blends of refrigerants whose liquid phase and vapor phase have the same compositions at a specific pressure).

Standard 34 assigns an identifying reference letter and number to each refrigerant to classify it according to the hazard involved in its use.

The fact sheet also refers to ASHRAE standard 15, Safety Standard for Refrigeration Systems, which puts requirements in place to help protect people and property where refrigeration facilities are located.

There is also a detailed table outlining a list of the approved refrigerant numbers from the latest edition of Standard 34 and addenda that were assigned from 2010 onward.

The fact sheet is available to download on the ASHRAE website.

The release comes after ASHRAE and UNEP approved a new two-year work plan in February, titled Life Cycle Refrigerant Management (LCRM).

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