Most commonly used refrigerants, such as hydrofluorocarbons, are potent greenhouse gases when they leak. Pound for pound, these refrigerants warm the atmosphere thousands of times more than carbon dioxide; it is critical to measure and understand their impact, especially as the use of heat pumps and air conditioners intensifies. Direct measurements from 126 San Francisco Bay Area homes show that residential central air conditioners leak about 1.8% of their refrigerant per year during operation, a fraction of the 4–10% assumed in most climate accounting. While these values come from pilot data in only one location, if they hold more broadly, they can help us prioritize where in the refrigerant lifecycle to intervene to stop leaks, develop more accurate greenhouse gas inventories, and better assess the safety of flammable natural refrigerants. 

PSE Healthy Energy, in collaboration with Stanford University, published a new peer-reviewed study in Environmental Research Letters that provides insight into quantifying refrigerant leakage in residential central air conditioners.

Residential central air conditioners leak about 1.8% of their refrigerant per year during normal use. 

The largest 1% of residential leaks account for 80% of total climate emissions from leakage.

At most, roughly 0.02% of residential central AC units lose their entire charge each year, a prerequisite for potentially flammable conditions to form when flammable refrigerants are used. Even among units that lost their entire charge, many additional things need to go wrong for dangerous conditions to form. Thus, if the loss frequencies we measured with units using non-flammable refrigerants hold for units abroad using flammable refrigerants, the true danger of switching to flammable refrigerants appears very low.

Using a 20-year global warming potential, researchers scaled the warming potential of leakage across the 2.15 million central AC units in mild-climate California and found that the annual leakage emissions are equivalent to about 160,000 gasoline-car emissions. It is important to note that this doesn’t mean that overall refrigerant leakage is a smaller problem than thought; it means that more of the leakage is occurring elsewhere in the lifecycle, such as during production and at end-of-life.

There are roughly 60 million modern residential central AC units in the U.S., yet almost no direct field data on how much they actually leak. This is one of the first studies to address this issue.

Air conditioners and heat pumps run on refrigerants, which, when leaked, can warm the planet substantially more than the same amount of carbon dioxide. For decades, no one had directly measured how much refrigerant actually leaks from the systems in individual homes during everyday use and had relied on old data from commercial spaces for their climate calculations. This is one of the first regional studies to measure leakage in residential spaces and shows that much less is being released during the regular operation of residential units than previously thought. As a result, this study provides a more accurate foundation for updated climate calculations, suggests the safety of environmentally benign natural refrigerants, and demonstrates that we should shift the focus toward production and end-of-life recovery of these refrigerants.