Air conditioning prevented an estimated 5,267 heat-related deaths each year across the contiguous United States, cutting heat-attributable mortality by 57%. The strongest gains occurred as AC use rose from low to moderate levels. Beyond median usage, additional cooling produced little extra reduction in mortality. Affordability remains a major obstacle. More than a quarter of U.S. households report difficulty paying for energy, limiting their ability to use AC when temperatures become dangerous. Air conditioning can make the difference between surviving dangerous heat and becoming another heat-related death, but simply turning the thermostat lower does not keep adding protection. A nationwide analysis from Yale University estimates that household air conditioning prevented 5,267 heat-related deaths each year across the contiguous United States. That amounts to a 57% reduction in heat-attributable mortality, offering one of the clearest measurements yet of how much residential cooling protects people as temperatures rise. The study, published in Nature Health, examined nearly 30 million death records from 3,108 counties between 2010 and 2020. Unlike previous research that largely measured whether households owned air conditioners, …