What’s the best temp for when nobody is in the house? What’s the best A/C temperature for sleeping? According to the report, you should set your thermostat to 78 degrees Fahrenheit when you’re home, 85 degrees when you’re at work or away, and 82 degrees when you’re sleeping. When we surveyed my Popular Mechanics colleagues, many were in agreement that 82 degrees is indeed an insane sleeping temperature. If you’re trying to keep your energy costs down, here’s the best way to cool down a room without blasting A/C .