AUSTIN — A research team at the University of Texas at Austin conducted a citywide study simulating indoor heat risks during power outages, finding that 85% of single-family homes in Austin would reach deadly temperatures for elderly occupants during a three-day heat wave above 110°F without air conditioning. The study simulated indoor temperatures for each of Austin's 213,000 single-family homes during these conditions.

The research combined Austin’s tax appraisal records with U.S. Department of Energy building energy simulation models. Under current climate conditions in Austin, about 15% of homes could reach temperatures posing serious heat risks to healthy adults without air conditioning. Newer, well-insulated homes maintained survivable temperature and humidity conditions for elderly occupants during the simulated blackout.

Indoor heat can exceed outdoor temperatures during a heat wave. When power fails and air conditioning stops, a house can function like a greenhouse, trapping heat entering through windows and walls. Indoor temperatures can rise above outdoor temperatures within hours, particularly on upper floors and in rooms with south-facing windows. Most heat-related deaths occur indoors.

During the 2021 Pacific Northwest heat dome, 98% of more than 600 deaths in British Columbia occurred inside homes. Washington and Oregon also recorded high numbers of heat-related deaths in homes lacking air conditioning during that 2021 heat wave. Poorly insulated homes release absorbed heat slowly, keeping indoor temperatures elevated overnight, and after two or three nights of elevated indoor temperatures, healthy people face serious risk for heat-related illnesses.

Human core temperature is approximately 98.6 degrees Fahrenheit (37 degrees Celsius). High air temperature weakens convective cooling of the human body, and high humidity prevents sweat from evaporating, reducing the body's ability to release heat. Human thermoregulation begins to fail when core temperature exceeds approximately 104 F (40 C), and death becomes likely when human core temperature exceeds 109 F (42.8 C).

Why It Matters

This study highlights the potential for widespread heat-related fatalities in Austin due to power outages during extreme heat events, particularly impacting vulnerable populations like the elderly. The findings indicate that the majority of single-family homes could become dangerous. The study utilized comprehensive local data and established simulation models to assess heat risk in residential buildings.

According to climate projections for Austin, the frequency of heat waves is expected to double by the end of the century. Under future warming scenarios where average summer highs reach 104 F (40 C), up to 65% of homes in Austin could pose serious heat risks to healthy adults. This projection suggests an increasing threat to public health in the region over time.