When it’s 110 F (43.3 C) outside, older houses will likely feel at least 10 F (5.6 C) warmer inside, even with the same air temperature. Why?
The answer has to do with radiant heat. Radiant heat is what keeps you toasty warm at a campfire on a cold winter night. The fire doesn’t warm the air much; rather, like the Sun, most of the fire’s heat moves through invisible waves directly from the campfire to your body.