People often ask whether I think the current transition to mildly flammable (A2L) refrigerants in comfort cooling equipment will be the last one, and my answer is an emphatic “no.” And the reason for that is nothing in the realm of HVAC technology and environmental regulations remains static; it is always evolving.

As evidence, I point to the last refrigerant transition, which started in 2010 and ended in 2020 with the final phaseout of HCFCs such as R-22. Back then, many believed it would be the final transition, given that HFCs such as R-410A had zero ODP, which is why HCFCs were phased out in the first place. While it was accurate that HFCs like R-410A did not harm the ozone layer, they were soon considered to be contributors to global warming, so another transition started to be contemplated almost immediately.

This time around, most experts agree that the transition in comfort cooling equipment from R-410A to A2Ls such as R-32 and R-454B is an interim solution and that a move to even lower-GWP options is all but certain. In fact, some on the California Air Resources Board (CARB) have already said that they want to get to 0 GWP in air conditioning equipment. To reach that goal, CARB has started developing an assessment report that will specify how to transition away from HFCs to ultra-low GWP and/or no-GWP alternatives no later than 2035.

So what could come after A2Ls in comfort cooling equipment? Many believe that R-290 (propane) could be the next candidate, as this refrigerant features a GWP of 3 and zero ODP. However, it is a flammable (A3) refrigerant, which means codes and standards in the United States would need to be updated before it could be used in residential split systems. This could prove challenging, considering the difficulties encountered in updating codes and standards for the use of mildly flammable (A2L) refrigerants in comfort cooling applications.

But in Europe, the transition to A3 refrigerants is already underway, with numerous manufacturers already introducing R-290 air-to-water heat pumps. Some of the companies that have rolled out R-290 heat pumps in Europe and the United Kingdom (UK) include:

• Bosch, featuring the Compress 5800i AW and Compress 6800i AW air/water heat pumps that use R-290 and are available in seven output ratings, including 10 and 12 kW. The company states that the heat pumps are future-proof, fully electric, quieter than ever, and suitable for almost any application.
• Mitsubishi Electric, whose Ecodan R290 heat pump has a guaranteed operation range down to -25°C ambient temperature and utilizes the refrigerant R-290 to achieve high water temperatures up to 75°C and a low GWP. The company states that the Ecodan R290 heat pump is the perfect renewable alternative to conventional fossil fuel boilers.
• Panasonic, which offers the Aquarea L Series air-to-water heat pumps that utilize R-290 and are designed for home renovations with existing radiators. The company says the units deliver water outlet temperatures ranging from up to 75°C to as low as -10°C and provide domestic hot water up to 65°C without the need for a heater for tank sterilization.
• Samsung’s EHS Mono R290 heat pump provides a consistent supply of high hot water temperature, reaching up to 75°C, making it an ideal candidate for renovations and retrofits. In addition to using R-290, the company states the heat pump can deliver a 100% heating performance in temperatures as low as -10°C.

Granted, the European and UK markets differ from the U.S., where air-to-air heat pumps are predominantly used in the residential market, instead of the air-to-water models prevalent overseas. As such, experts say it would be difficult to use propane in a split system here, as the refrigerant is located in the home instead of staying outside, as in Europe. However, do I believe that some ultra-low-GWP solution will eventually make its way into the U.S.? Almost certainly. We just have to wait and see what that may look like.