Change has become commonplace among HVACR contractors – and more change is coming. The industry will once again face disruptions as the EPA enacts the Technology Transition Program beginning Jan. 1, 2025. In this phase of the American Innovation in Manufacturing Act, HVAC manufacturers will be prohibited from producing residential and light commercial unitary equipment that uses refrigerants with a global warming potential (GWP) over 700.

As a result, these new HVAC systems will be designed to use low-GWP, A2L refrigerants such as R-454B. Although the ruling still allows the sell-through of split system condensers, coils and air handlers manufactured in 2024 or earlier as new systems through Dec. 31, 2025, and factory-charged single packaged products manufactured in 2024 through Dec. 31, 2027, contractors can expect to see new equipment using A2L refrigerants hit the market now and into 2025.

The introduction of this new equipment means contractors will need to understand a whole new standard of protocols required for A2L refrigerants.

Understanding RDS

Because A2L refrigerants possess mildly flammable characteristics, ASHRAE Standard 15.2 and 34 as well as UL 60335-2-40 (4th edition) have been updated with requirements that must be followed when installing residential packaged and split HVAC systems.

Within these guidelines is the addition of a refrigerant leak detection system (RDS) to maintain safe operation in the event of an A2L refrigerant leak. If a leak occurs, sensors located in the airstream near the evaporator coil will activate control logic to initiate an alarm sequence that automatically shuts down any active call for heating or cooling and activates the indoor blower to dilute any A2L refrigerant that is present. 

Not all residential applications need an RDS. Determining when the system is necessary requires knowledge of the building envelope, potential ignition sources, size of equipment and refrigerant charge volume vs. free air space – calculations which are the responsibility of the installing contractor.

In general, an RDS is required if the total charge is above four pounds, there is a potential ignition source in close proximity and/or electric heat is installed within the equipment. Alternately, an RDS may not be needed if the charge of the largest circuit is less than four pounds.

Application-specific assessment is critical for proper determination of RDS requirements. For example, even if the job has a charge under four pounds, an RDS and additional venting may be necessary if the equipment is installed within a confined space.

Additionally, gas heating units may require an RDS if the installation doesn’t meet minimum area requirements or charge volumes in the equipment exceed maximum limits. Contractors must also understand any state and local codes that have been adopted and ensure those requirements are also met.  

Determining if an RDS is required places even more importance on the need for HVACR contractors to know their local building codes as well as application and safety standards, but this can leave contractors with a hefty workload when in the field. 

Calculation process

Smart tools like the Johnson Controls Ducted Systems Solutions App can streamline the RDS calculation process and help to ensure compliance with ASHRAE and UL standards. In addition to resources such as installation guides and troubleshooting support, the free app provides contractors with an RDS Calculator tool to save time in the field and ensure accurate calculations are made.

After determining the size of equipment and duct work and performing load calculations, contractors can leverage the RDS Calculator tool as a straightforward approach to work through RDS requirements. Utilizing input from the air discharge height, total area being conditioned, potential individual zone impact and the potential presence of any sustained ignition sources, the calculator provides an instant report including RDS rationale as well as any additional mitigation protocols that may be recommended, such as whether exhaust air is required in the conditioned space.   

As the HVACR industry continues to evolve, it is important to remember that building knowledge and perfecting protocols is a journey taken over time.

Understanding ASHRAE application and UL safety standards as well as being aware of state and municipal requirements are critical first steps. Maintaining proven best practices for evaluating the building envelope and understanding application-specific parameters, including load calculations and duct design, are also crucial – even as installation protocols shift. Smart tools such as RDS calculators can help to streamline new processes and save time in the field as contractors continue to build knowledge and gain experience around these emerging requirements.

Zac Wempe serves as regional technical service manager, North America, for Johnson Controls Ducted Systems. Over the past eight years at Johnson Controls, Zac has progressed through roles including engineering lab technician; dealer technical support, and distributor technical support, before stepping into his current role as an RTSM.