This HAS to be sweatiest movie since Cool Hand Luke--but that was set in a Depression-era prison in the South. Body Heat was set in modern-day Florida--they DID have air-conditioning by then. Yes, it's humid down there--but not indoors in commercial establishments and upscale homes.
shareThe bonus features include interviews with the director and main actors.
It seems that the movie was supposed to be set and filmed in New Jersey. Then, when filming could begin, it was winter, so they moved the locale to Florida.
Sounds good, except that Florida had one of their coldest winters on record.
Those actors were freezing, and not sweating, they had to be sprayed down with water all the time. Plus, in order to not let their breaths "steam up" outside when they were talking, they had to put ice in their mouths and spit it out just before dialog, ---otherwise, you'd see how cold it really was.
Anyway, since it was supposed to be set up north, probably they didn't have as much air conditioning as Florida, but who knows.
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It worked, all the sweat made the film hugely atmospheric! Like "Vertigo", where as you watch you can feel the chill of the late afternoon fog as it wafts in from the sea and covers San Francisco, in "Body Heat" your imagination tells you that you feel hot and sticky, and that you can smell the moisture in the air and the lukewarm sea, the smog from the traffic and the greenery and garbage of the town, because that air isn't moving.
As for the William Hurt character not having air conditioning in his office, it was a good way to establish him as low-rent, unsuccessful, and literally itching with the need for more money. If you're in Florida and can't afford air conditioning, or fixing your air conditioner, you are both physically and socially uncomfortable.