Charge Limits for Safety Class A3 Refrigerants

List author as:

Chris Mobley, Senior Regulatory Engineer, Codes and Regulatory Services, UL Solutions

This article provides an overview of the common applications of mechanical refrigeration appliances using safety class A3 (flammable) refrigerants. It covers the charge limits for these systems along with the related requirements of the model mechanical codes.

This information is general in nature and is based on typical scenarios. Always refer to the individual product certifications, the reference standards and the locally adopted codes for specific information.

The refrigerants used in the air conditioning and refrigeration industries continue to evolve due to federal regulations based on the global warming potential (GWP) of refrigerants. Much of the attention has been focused on the new class of A2L refrigerants. However, small systems using class A3 refrigerants are also becoming common.

Class A2L refrigerants have moderate heat of combustion and propagate flame with low burning velocity. By contrast, class A3 refrigerants are highly flammable and explosive.

Refrigerants designated as class A3, along with their formulas and properties, can be located in the tables in the model mechanical codes and ASHRAE 34. The most common class A3 refrigerants are familiar compounds:

• R-290 (propane)
• R-600a (isobutane)
• R-1270 (propylene)

As a point of reference, liquefied petroleum (LP) gas is defined as a mixture of these three hydrocarbon gas compounds. However, readers should be aware of several key differences between a fuel gas and a refrigerant application, namely:

• Class A3 refrigerants do not contain odorants such as mercaptan. The odorant compounds used in fuel gas would be contaminants in a refrigeration system. An electronic detector designed for class A3 refrigerants can be used to detect a leak of these refrigerants.
• Mechanical refrigeration systems using class A3 refrigerants typically operate at pressures ranging from approximately 150 psi to 200 psi (1,000 kPa to1,400 kPa) as compared to low-pressure fuel gas distribution piping and appliance regulators that typically operate less than 1 psig (7 kPa).
• Mechanical refrigeration systems contain much lower quantities of gas compared to fuel-gas systems.

Split systems, with field provided interconnecting piping, are not common and may have additional installation restrictions per the model codes. Some common self-contained systems include the following products:

• Commercial refrigerators, appliances and case coolers (UL 60335-2-89)
• Household refrigerators and ice makers (UL 60335-2-24)
• Commercial ice makers (UL 60335-2-89)
• Household ice cream machines (UL 60335-2-24)
• Commercial ice cream machines (UL 621)
• Room dehumidifiers (UL 60335-2-40)
• Room/window air conditioners (UL 60335-2-40)
• Refrigerated vending machines (UL 541)
• Drinking fountains and bottle filling stations (UL 399)
• Heat pump clothes dryers and laundry stations (UL 2158)

For each of the above applications, the applicable standard sets charge limits for class A3 refrigerants. In most cases, other than commercial refrigeration appliances certified to UL 60335-2-89, the upper charge limit is either 130 g or 150 g (0.29 lb. or 0.33 lb.). For many applications, including any use in a public corridor or lobby (as defined by ASHRAE 15), the charge is further limited to “3 × LFL” (where the LFL is the gram value of the lower flammability limit in kg/m^3.).

Some commercial refrigeration appliances certified in accordance with UL 60335-2-89 can have somewhat higher charge limits.

For open case coolers with no doors or drawers, the charge can be up to “13 × LFL.” Appliances with doors and drawers can have charges up to “8 × LFL” (again, where the LFL is the gram value of the lower flammability limit in kg/m^3.).

Appliances with these higher charge limits have additional installation restrictions per the model codes and/or the manufacturer’s installation instructions:

• Cannot be installed within 20 ft. (6 m) of an open flame source
• Cannot be installed in a public corridor or lobby (as defined by ASHRAE 15)
• Cannot be installed in residential occupancies

As the charge limits in the product standards evolve, in some cases there may be a misalignment between the product standards and the codes.

• The 2024 editions of the model mechanical codes set a limit of 0.331 lb. (150 g) for most indoor applications of class A3 refrigerants, other industrial occupancies or within designated machinery rooms.
• The 2027 editions of the model mechanical codes will allow larger charges for commercial refrigeration equipment certified in accordance with UL 60335-2-89, as previously described.

• International Mechanical Code (IMC)
• Uniform Mechanical Code (UMC)
• ASHRAE 15, Safety Standard for Refrigeration Systems
• ASHRAE 34, Designation and Safety Classification of Refrigerants
• UL 60335-2-24, the Standard for Household and Similar Electrical Appliances – Safety – Part 2-24: Particular Requirements for Refrigerating Appliances, Ice-Cream Appliances and Ice-Makers
• UL 60335-2-89, the Standard for Household and Similar Electrical Appliances – Safety – Part 2-89: Particular Requirements for Commercial Refrigerating Appliances and Ice-Makers with an Incorporated or Remote Refrigerant Unit or Motor-Compressor
• UL 60335-2-40, the Standard for Household and Similar Electrical Appliances – Safety – Part 2-40: Particular Requirements for Electrical Heat Pumps, Air-Conditioners and Dehumidifiers
• UL 541, the Standard for Refrigerated Vending Machines (UL Solutions product category SQMX)
• UL 399, the Standard for Drinking-Water Coolers (UL Solutions product category SRJX)
• UL 621, the Standard for Ice Cream Makers (UL Solutions product category SINX)
• UL 2158, the Standard for Electric Clothes Dryers (UL Solutions product category KMEX)