Yeah, bathroom vents can be sneaky culprits for sure. Have you checked if the ducting is insulated properly? Had a similar issue myself—thought it was...

You're not alone—most folks don't even realize there's supposed to be a "schedule" until something goes wrong. I've been in my house for about 8 years...

I've thought about the frosted film too, but does it hold up well over time? I've seen some windows where it starts peeling at the corners or bubbling...