The quest to fix the irony at the heart of every heat pump

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.

“The whole industry is going to be transitioning away from R-410A, so that’s good,” said Jeff Stewart, the refrigeration chief engineer for residential heating, ventilation, and air conditioning at Trane Technologies, which makes heat pumps and gas furnaces. “We’re getting lower global warming potential. The problem is, it still has some, right? So there’s concern about ‘OK, is that low enough to really help the environment?’”

To be clear, heat pumps do not release greenhouse gases at anywhere near the scale of burning natural gas to heat homes, so their environmental impact is way smaller. “Even if we lost all the refrigerant, it still actually has a much smaller effect just having a heat pump and not burning gas,” said Matthew Knoll, co-founder and chief technology officer at California-based Quilt, which builds heat pump systems for homes. “I would actually want to make sure that doesn’t hamper the rapid adoption of heat pumps.”

But why does a heat pump need refrigerant? Well, to transfer heat. By changing the state of the liquid to a gas, then compressing it, the appliance absorbs heat from even very cold outdoor air and moves it indoors. Then in the summer, the process reverses to work like a traditional air conditioner.

The potential for refrigerant leaks is much smaller if the heat pump is properly manufactured, installed, and maintained. When a manufacturer switches refrigerants, the basic operation of the heat pump stays the same. But some formulations operate at different pressures, meaning they’ll need slightly different sized components and perhaps stronger materials. “It’s all the same fundamental principles,” said Vince Romanin, CEO of San Francisco-based Gradient, which makes heat pumps that slip over window sills. “But it does take a re-engineering and a recertification of all of these components.”

While Trane has transitioned to R-454B, Gradient and other companies are adopting R-32, which has a global warming potential of 675 and brings it in line with the new regulations. Gradient says that with engineering improvements, like hermetic sealing that makes it harder for refrigerants to escape, and by properly recycling its appliances, it can reduce the climate footprint of heat pumps by 95 percent. “Our math shows R-32, plus good refrigerant management, those two things combined solve almost all of the refrigerant problem,” said Romanin. “Because of that data, Gradient believes the industry should stay on R-32 until we’re ready for natural refrigerants.”

Those include CO2, butane, and propane. CO2 has a global warming potential of just 1, but it works at much higher pressures, which requires thicker tubes and compressors. It’s also less efficient in hot weather, meaning it’s not the best option for a heat pump in cooling mode in the summer.

Propane, on the other hand, excels in different conditions and operates at a lower pressure than the refrigerants it would replace. It also has a global warming potential of just 3. Propane is flammable, of course, but heat pumps can run it safely by separating sources of ignition, like electrical components, from the refrigerant compartments. “It is kind of perfect for heat pumps,” said Richard Gerbe, board member and technical advisor at Italy-based Aermec, another maker of heat pumps.

That’s why Europe is already switching to propane, and why the U.S. may soon follow, Gerbe said. A typical heat pump will run about 10 pounds of propane, less than what’s found in a barbeque tank. Gas furnaces and stoves, by contrast, are constantly fed with flammable natural gas that can leak, potentially leading to explosions or carbon monoxide poisoning. “If you’ve got a comfort level with a gas stove in your house,” Gerbe said, “this is significantly less of a source.”

This story was originally published by Grist with the headline The quest to fix the irony at the heart of every heat pump on Apr 4, 2025.