Those fans suck "conditioned air" out from the house interior and send to the outside. That air is replaced by outside warm, humid, air that leaks into the house.

Get it?

Which is why you should have a fresh air make up air system that is tied into your home’s HVAC. If your hood is over 400 CFM, its a code requirement. And it needs to be a lot bigger.

I see. Tha makes sense. I actually thought it was helping, to remove the warm humid from those rooms. Didn’t realize it was also removing conditioned air. Thanks.

Joseph, I think our 22+ year old Kenmore hood is 350 cfm, and our 60-year-old windows are kind of leaky, so I think we are good there. (except for the windows that have 3M insulating film on them.)

Huh?

Film on windows doesn't have any effect on air leakage around or through the frames.

Exhaust fans (whether in the kitchen or a bathroom) can only exhaust the amount of air that enters the home to replace it. In a tight home, with no means for outside air to enter, a fan will turn but little will be exhausted.

We always crack a window nearby the exhaust fan (in the same room or an adjacent room), when showering or using the one over the range. You'd be surprised what a big difference it makes.

"and what about bathroom exhaust fans?"

It would be true for them too. I guess the definition of "excessively" is for the home owner to determine.