Residential San Francisco Bay area air conditioners leak less refrigerant than expected

Building electrification, rising living standards, and increasing temperatures are all driving adoption of air conditioners and heat pumps. Many commonly used refrigerants, such as hydrofluorocarbons, are potent greenhouse gasses when they leak and contribute substantially to total anthropogenic radiative forcing, unlike natural refrigerant such as propane. While research and policy attention directed towards refrigerant management have emphasized the commercial sector, few empirical studies have directly quantified refrigerant leakage among the ∼60 million modern residential central air conditioners in the United States alone. We estimate refrigerant leak rates during normal operation from residential central air conditioners using new direct measurements from 126 San Francisco Bay Area homes combined with published datasets. Residential central heating, ventilation, and air conditioning (HVAC) units in our sample geography leak an estimated 1.78% [95% CI: 0.83, 2.73] of their charge annually on average, a value far lower than most current values used in lifecycle assessments or greenhouse gas budgets. Leaks from residential units are extremely long-tailed, more so than in the commercial sector, with the top 1% of residential leaks accounting for 80% of total CO 2 equivalent leakage emissions. Complete loss of refrigerant charge is probably rare; we estimate that roughly one in every 5000 homes (0.02%) and at most 0.09% of residential central HVAC units in our sample geography lose their entire refrigerant charge indoors each year. These results provide a quantitative basis for evaluating refrigerant-related climate impacts of residential HVAC systems. They suggest that, in the residential sector, efforts to mitigate leakage during use may be a lower priority than mitigating refrigerant release elsewhere in the supply chain (for instance, during production and at the end of an AC unit’s life). Our measurements also provide a basis for assessing the flammability risk of natural hydrocarbon refrigerants.