How much air conditioning usage actually prevents heat deaths?

How protective is air conditioning in preventing deaths amid soaring temperatures and record heat levels? Yale researchers found that AC use cut the number of annual heat-related deaths by half in the U.S., saving more than 5,000 lives a year. However, while AC is a highly effective heat adaptation tool, its protective effects level off once use passes a certain point. On days of extreme heat, risk levels tick up even with use.