A friend saw the same thing in her kid's school.

I read somewhere that a good audit should include a blower door test, which actually measures how leaky your house is instead of just guessing. Sounds like your guy skipped that part and still charged you full price. Might be worth asking the next company if they do that before you hand over any money.

How hot is your cheap hair dryer actually getting? Because that number matters way more than the 90 seconds does. Most of those dryers run 120 to 140 F on low, which is right in the sweet spot for old grease, but a "low" setting on a hot running dryer can hit 170 or more and that is where you start messing with cement and paint. My move is to check it with an infrared gun before it goes anywhere near the glass, point it at the barrel right where the ring meets it, and stop when the metal reads about 110 to 120 F. That gives the grease enough to let go without ever getting the front element warm. Takes an extra ten seconds and you never have to guess.