Austin Home Simulations Show Indoor Heat Exceeds 100°F for Healthy Adults After 48 Hours Without AC

The University of Texas study merged county tax-appraisal records with U.S. Department of Energy building archetypes to run three-day heat-wave simulations. Older single-pane homes retained heat through the night while newer double-pane units delayed but did not prevent peak indoor temperatures above 100 °F. These modeled trajectories match the 2021 Pacific Northwest event in which 98 % of British Columbia’s 600-plus fatalities occurred indoors.

European data provide scale: an estimated 107,000 heat deaths occurred across the continent in 2022–2023, the large majority inside dwellings never designed for sustained 95 °F-plus conditions. The Austin results add granularity by showing that two adjacent homes on the same street can differ by 12–15 °F indoors solely because of vintage and insulation, a disparity the original reporting under-emphasized.

Nighttime radiative cooling from walls and ceilings keeps core body temperature elevated, pushing healthy adults toward the 104 °F thermoregulatory failure threshold after 48–72 hours. Passive measures such as cool roofs and targeted mechanical ventilation were absent from the original coverage yet could lower indoor peaks 4–6 °F according to separate DOE field trials.

Next-step research must pair these archetype models with distributed indoor sensors across multiple climates and test whether city-level retrofit mandates reduce heat-related emergency visits by the 20 % threshold projected in recent Lancet Planetary Health scenarios.