Every now and then I run across a scene that is &quotin a sauna", but without exception it is always obvious that the action takes place at normal temperature and the performers have just been sprayed with water before starting (no sweat rolls down their forehead at any point in the action, her makeup stays flawless, etc.). I'm guessing it is bad for the video camera to film a scene in a room that's at 150+ degrees Fahrenheit, and if so that's a shame.
Still, can anyone think of examples of scenes where the people fucking are sweating profusely from the conditions in the room? Perhaps an infrared sauna might work (particularly if the camera was covered in reflective foil). I remember a scene from Digital Playground where Bruce Venture was fucking August Ames on an airplane set, where the lights were so hot that both of them were a complete mess halfway through (he was constantly dripping sweat on her tits, and it looked awesome), but obviously that wasn't intentional.