The Air-Conditioning, Heating, and Refrigeration Technology Institute (AHRTI), the research arm of the AHRI, has been awarded a $1.5 million (€1.26 million) grant to support “essential research on the risk assessment” of residential monobloc air-to-water heat pumps (ATWHPs) using higher charges of A3 (flammable) refrigerants in North America, according to an announcement from AHRI on LinkedIn.
The grant comes from the North American Sustainable Refrigeration Council (NASRC) through its F-gas Reduction Incentive Program (FRIP), which is funded by the California Air Resources Board (CARB). It makes up for funding that had been expected from the U.S. Department of Energy (DOE) but was delayed. Last September NASRC solicited proposals from qualified third-party subcontractors to conduct this risk assessment.
The AHRTI, under the direction of Xudong Wang, Vice President of Research for the AHRI (Air-Conditioning, Heating, and Refrigeration Institute) , will lead the project in collaboration with the Oak Ridge National Laboratory (ORNL). The researchers will conduct a comprehensive flammability risk assessment of A3 refrigerants, particularly propane (R290), in ATWHPs “under different residential installation configurations and lifecycle events,” said AHRI.
Notably, monobloc ATWHPs restrict the propane refrigerant to the outside equipment, reducing the risk to end users. These appliances have been widely used in Europe since 2023 with R290 charges up to (4.94kg/10.9lbs) based on the global standard IEC 60335-2-40.
However, in North America, the Underwriters Laboratories (UL) limits the use of R290 to 114g for all HVAC residential and light-commercial applications under its most recent (fourth) edition of the UL 60335-2-40 standard. The ASHRAE-15 standard also significantly restricts A3 refrigerant use in residential and commercial applications to less than 150g with any larger amount requiring approval by a local jurisdiction’s code officials. These charge limits currently make the adoption of monobloc R290 ATWHPs in North America challenging.
“I’m excited to lead this major research initiative.”
Xudong Wang, Vice President of Research for the AHRI
Findings from the new research will be used to “generate sound technical knowledge” for the safe use of ATWHPs with A3 refrigerants in the North American market and to “inform codes and standards bodies” like UL and ASHRAE as they update safety standards and building codes to protect consumers, technicians and laboratory personnel, added AHRI. The updated standards would allow higher charges of A3 refrigerants like propane, thereby facilitating the rollout of A3-based ATWHPs in North America.
“I’m excited to lead this major research initiative,” said Wang in a LinkedIn post. “I look forward to collaborating with leading experts from AHRI member companies, Oak Ridge National Laboratory and other key stakeholders. Grateful to the California Air Resources Board for its funding support.”
Wang will be providing an update of the A3 research at the Next-Generation Refrigerants Workshop, to be hosted by the Oak Ridge National Laboratory, April 8-9, 2026, in Oak Ridge, Tennessee.
North America catching up
The latest version (edition 7) of IEC 60335-2-40 was approved in 2022 after a decade of research, testing and international cooperation. It allows up to 988g of R290 in HVAC units located indoors or connected to the indoor space, such as ductless split ACs or ducted central systems; these are subject to room size limits and other equipment design requirements. It also allows 4.94kg of R290 in outdoor/indirect systems such as ATWHPs, among other limits. Europe and other regions have fully harmonized with the global IEC standard.
In North America, both UL and ASHRAE have undertaken efforts to raise the charge limit for A3 refrigerants in their standards to be in alignment with the IEC. The UL last year announced formation of a Technical Harmonization Committee (THC), which began meeting in October 2025 to develop the fifth edition of UL 60335-2-40. This committee is expected to consider proposals on a range of topics related to equipment safety, including requirements related to flammable refrigerants.
In 2023 ASHRAE’s SPCC Subcommittee 15.2 began considering a change to the ASHRAE 15 standard that would allow the use of up to 4.9kg of A3 refrigerants in outdoor (indirect) heat pumps and air conditioners (such as ATWHPs) in the U.S. This change would be dependent on research confirming the safety of the higher charge limit; to that end, in 2024 SPCC Subcommittee 15.2 formed a working group, which developed a “work statement” to do computational-fluid-dynamics (CFD) and verification testing under the direction of Wang, who is now leading that research.
If approved by UL and ASHRAE, the higher charge would also need to be endorsed by the U.S. Environmental Protection Agency (EPA); it would also be incorporated in the next model and state building codes. Twenty-three states have already passed legislation that would enable this use of hydrocarbons (in addition to A2Ls), once UL 60335-2-40 and ASHRAE 15 are updated and EPA SNAP (Significant New Alternatives Program) approved.
The U.S. branch of the Environmental Investigation Agency (EIA) said in a 2025 report that it supports full harmonization of U.S. standards on the use of hydrocarbon refrigerants in HVAC equipment with the global standard IEC 60335-2-40. This could enable 78–88% of new air-conditioning and heat-pump equipment in the U.S. to transition to propane between 2030 and 2035, according to the EIA.
