Heat pumps are essential for ditching fossil fuels. The appliances are many times more efficient than even the best gas furnaces, and they run on electricity, so they can draw power from renewables like wind and solar.

But the very thing that makes them such an amazing climate solution is also their biggest challenge. A common refrigerant called R-410A pumps through their innards so they can warm and cool homes and offices and anything else. But that refrigerant is also liquid irony, as it can escape as a greenhouse gas over 2,000 times more powerful than carbon dioxide. (This is known as its “global warming potential,” or how much energy a ton of the gas absorbs over a given amount of time compared to the same amount of CO2.) Leaks can happen during the installation, operation, and disposal of heat pumps.

But this year the industry is rolling out alternative refrigerant formulations like R-454B and R-32, which have around 75 percent less global warming potential. That’s in response to Environmental Protection Agency rules mandating that, starting this year, heat pump refrigerants have a global warming potential of no more than 700. Manufacturers are looking even farther ahead at the possibility of using propane, or even CO2, as the next generation of more atmospherically friendly refrigerants.