fail to feel hot...
Somehow, the way they shoot this movie, just doesn't give me the life threatening of heat as movies like "Lawrence of Arabia", "The Kingdom" or "Tears of the Sun". I know I'm comparing a entirely different class of movies, but those actually gave me that danger of heat like the blast of the sun, the burning heat that flush down your lung, the sweat that constantly run down your chest... In "247°F", characters didn't sweat much until very late in the sauna, and when they sweat they just "wet" and not "dripping sweat", their hair and clothes weren't that wet, and the CG air current just make it look worst.
I think the visual effect would be better if it took place in a steam room rather than sauna.