Guidance on A2L Refrigerant Systems and Retrofits in Legacy Air Handlers

As the industry transitions to lower-GWP refrigerants under the AIM Act technology transition, many new residential and light commercial systems will utilize A2L refrigerants (such as R-454B/R-32). These refrigerants introduce additional safety requirements that directly impact how HVAC equipment must be designed and installed.

We have recently seen questions from contractors about installing third-party evaporator coils, metering devices, and aftermarket A2L leak detection sensors into older air handlers that were originally designed for A1 refrigerants (such as R-410A).

It is important that our teams understand and communicate the following:

1. A2L Systems Must Be Designed and Certified as a Complete Appliance

Equipment using A2L refrigerants must comply with UL 60335-2-40, the safety standard governing HVAC appliances containing flammable refrigerants.

Under this standard:

A Refrigerant Detection System (RDS) is required for many indoor units.
The sensor location and mitigation controls are part of the appliance safety design.
The sensor placement is determined during manufacturer testing and certification.

Because of this, the sensor location must be defined by the manufacturer and installed according to the manufacturer’s instructions.

2. Equipment Must Be Installed According to Its Listing

The International Mechanical Code (IMC) requires mechanical equipment to be installed in accordance with the manufacturer’s installation instructions and the conditions of the product listing.

This means:

HVAC equipment must be installed as tested and certified by the manufacturer.
Modifying equipment outside of that tested configuration creates an unlisted appliance.

3. Field-Engineering an A2L Appliance Is Not Permitted

Installing a combination such as:

a third-party evaporator coil
a new metering device
a third-party A2L leak sensor
inside an older air handler cabinet

creates a configuration that has not been tested or listed under UL 60335-2-40.

Because the air handler was not originally designed and certified for A2L refrigerants, adding aftermarket components does not make the equipment compliant.

4. Why Manufacturers Specify Sensor Locations

A2L sensors are typically installed near the evaporator coil and lower areas of the cabinet, where refrigerant is most likely to accumulate during a leak.

These locations are determined through leak dispersion and safety testing during product certification. As a result, manufacturers must specify the sensor mounting location as part of the equipment design.

5. Sales Guidance

When asking about converting or retrofitting older air handlers for A2L refrigerants, the correct guidance is:

A2L systems must be installed in equipment designed and listed for that refrigerant.
Legacy air handlers cannot be converted into compliant A2L appliances through aftermarket components.
The proper solution is to install equipment designed and certified for A2L refrigerants.

Key Takeaway

A2L refrigerant systems are not simply a refrigerant change. They involve specific safety controls, detection systems, and certified equipment configurations. Installing aftermarket components into legacy air handlers does not meet the UL safety standard or mechanical code requirements.

If there are questions about specific installations or equipment compatibility, please reach out to the Technical Support team.