Turning on the air conditioner can be the difference between a sweltering afternoon and a trip to the emergency room. New research from Yale University has put a precise number on that margin for the first time: household air conditioning prevents an estimated 5,267 heat-related deaths across the contiguous United States every year, cutting heat-attributable mortality by more than half. The Yale air conditioning heat deaths study is the first nationwide analysis to look at cooling use rather than just ownership.
The study, published Aug. 31, 2026, in Nature Health, also delivered a more surprising finding. Once a community reaches a moderate level of air conditioning use, cranking the thermostat lower does not save additional lives. It just costs more money, burns more electricity, and adds more emissions.
“Everyone agrees that air conditioning works, but knowing that it works for one person is not the same as knowing how much death it prevents across an entire population,” said Kai Chen, senior author of the study and an associate professor of epidemiology at the Yale School of Public Health.
The First Study to Measure Real AC Use, Not Just Ownership
Previous research on cooling and mortality relied on a simple proxy: how many households owned an air conditioner. That number tells you very little about who actually uses one or how often. A window unit in a closet does not save anyone from heat stroke.
To fix that, the Yale team matched nearly 30 million death records from 2010 through 2020 against estimates of how much electricity each U.S. county actually spent on cooling. Those electricity estimates came from FusionACS, a machine learning dataset developed by co-author Narasimha Rao’s lab at the Yale School of the Environment that merges U.S. household surveys with American Community Survey data.
“Our dataset enabled us to relate AC use to mortality and temperature at a meaningful spatial scale,” said Rao, a professor of energy systems. “This is one of many studies we are undertaking to understand how low-income households cope with extreme heat. While some choose to turn on their ACs, others make the uncomfortable choice of bearing the heat to save money for food.”
The Numbers: Where Air Conditioning Saves the Most Lives
Across 3,108 counties, the researchers found that air conditioning reduced heat-attributable mortality by an average of 57%. In counties with the lowest cooling usage, the hottest days of the year carried a 2.2% higher risk of death than the mildest, safest days. In counties at the national median for AC use, that excess risk dropped to 0.8%, a difference too small to be statistically meaningful. The findings add to a growing body of research linking rising temperatures to preventable deaths.
The biggest concentrations of averted deaths were in Florida, the Southwest, and along the Gulf Coast, the same regions where summer temperatures now stay dangerous for weeks at a time. The pattern is consistent with broader urban heat risk research showing that the same places facing the worst climate exposure also tend to have the fewest affordable cooling options.
Why “More AC” Does Not Mean “Fewer Deaths”
Here is the twist that makes the study matter for utility companies, city planners, and anyone who worries about their electric bill. Once a county passed the national median for cooling, the line went flat. Heavier use of air conditioning did not translate into measurably lower mortality.
The likely explanation, the authors wrote, is that residents in already-cooled communities are over-using AC on moderate days. They are running the unit to chase comfort instead of safety, and that extra runtime is not buying any extra health benefit.
That ceiling has real consequences. Pushing the same population to cool more aggressively would strain the grid, drive up residential electricity demand, and add to greenhouse gas emissions, all without saving additional lives. The implication for public health spending is sharp: the most lives are saved by expanding access to cooling in the places that still lack it, not by demanding deeper cooling in the places that already have it.
Who Is Still Left Out of Cooling
Air conditioning is nearly universal in American homes today, with about 88% of U.S. households owning some form of AC as of 2020 and the U.S. Census Bureau’s more recent Local Air Conditioning Estimates put that share at roughly 93% by 2023. Two-thirds of households rely on central air or a heat pump as their main cooling equipment.
Regional gaps remain large. About 92% of homes in the Midwest and 93% in the South have air conditioning, but only 73% in the West, where marine climates along the Pacific Coast still register as low as 49% in some tracts. For homes without central air, choosing the right ductless cooling setup can make a measurable difference in comfort and energy use.
Owning an air conditioner is not the same as running it, however. More than a quarter of U.S. households told surveyors they had difficulty affording their energy bills, a barrier that turns the AC into a luxury during the very heat waves it is meant to relieve.
Why Heat Kills So Many People
Heat stress is the leading cause of weather-related deaths worldwide, and exposure to extreme heat keeps growing as the climate warms. The last three years have been the hottest on record, and prolonged high temperatures are linked to heat exhaustion, heat stroke, cardiovascular disease, respiratory disease, and kidney disease. Older adults, outdoor workers, and people with chronic conditions are hit hardest.
The new study focuses only on the lives saved by air conditioning. It does not measure the harms AC itself can cause, including indoor air pollution from combustion-powered electricity, the urban heat island effect that worsens street-level temperatures, and the climate feedback loop created by the very energy sources that power the unit. The researchers also did not attempt to credit cooling centers, heat alerts, and local heat action plans, all of which almost certainly take some of the lives saved.
Key Takeaways From the Yale Study
- Household air conditioning prevents an estimated 5,267 heat-related deaths every year in the contiguous United States.
- On average, AC use cuts heat-attributable mortality by 57%.
- Once a community reaches moderate cooling levels, cranking the AC lower does not save additional lives.
- More than a quarter of U.S. households struggle to afford the energy needed to run their cooling.
- Researcher Robert Dubrow argues landlords should be required to provide cooling, just as they must provide heating.
- Energy assistance programs and weatherization upgrades target the neighborhoods where the next 5,000 lives are most likely to be saved.
What the Findings Mean for Policy and for Your Home
For housing policy, the implications are blunt. “Landlords in the United States are required to provide heating in the winter, and our study contributes to a compelling body of literature that indicates they also should be required to provide cooling in the summer,” said Robert Dubrow, a study co-author and founding faculty director of the Yale Center on Climate Change and Health.
For the average household, the message is more practical. If you have a working air conditioner, use it during heat waves, but understand that setting it to 68°F is not meaningfully better for your health than setting it to 78°F, even though it can double your electricity bill and add to the emissions that drive next summer’s heat in the first place. Homeowners who want to lower their cooling load can also review passive strategies for keeping a house cool without AC, which work well in tandem with moderate thermostat settings. The bigger health lever is making sure friends, neighbors, and renters without affordable AC have somewhere cool to go, because that is where the next 5,000 lives will be saved.
FAQ: Air Conditioning and Heat Risk
Is heat the number one cause of weather-related deaths?
Yes. Extreme heat kills more people in the United States each year than hurricanes, tornadoes, and floods combined, and the World Health Organization considers heat stress the leading cause of weather-related mortality worldwide.
How many Americans actually use air conditioning?
Around 88% of U.S. households owned AC in 2020, and newer Census experimental data put the share at roughly 93% by 2023. Two-thirds of homes rely on central air or a heat pump, and the rest mostly use window or wall units.
Is setting the thermostat lower better for your health?
Not really, according to the Yale data. Once a home is cool enough to take the strain off the heart and lungs, dropping the temperature further does not appear to save additional lives. It does, however, sharply increase energy use and the emissions that come with it.
What can you do if you cannot afford to run the AC?
Public cooling centers, libraries, and shopping malls are the most common fallback. The same neighborhoods that lack affordable cooling are also where local heat action plans, utility bill assistance programs, and weatherization upgrades deliver the largest drop in deaths, which is exactly where the Yale authors say the next wave of investment will save the most lives.
