Extreme Heat

When the temperature is at or above 150 degrees a creature exposed to the heat must succeed on a Constitution saving throw every 15 minutes or gain one level of exhaustion. The DC is 10 for the first hour and increases by 2 for each 15 minutes. Creatures wearing medium or heavy armor, or who are clad in heavy clothing, automatically fail.
Creatures with resistance or creatures naturally adapted to hot climates must succeed on a Constitution saving throw at the end of each hour or gain one level of exhaustion. The DC is 5 for the first hour and increases by 1 for each additional hour. Creatures wearing medium or heavy armor, or who are clad in heavy clothing, are at disadvantage.
Creatures immunity to fire damage automatically succeed on the saving throw.