I just replaced the bathroom exhaust fan motor assembly which is the fan motor, squirrel cage, and mounting plate. I did this because the fan is about 25 years old. The bathroom is only 36 square feet with 8 foot ceiling and the new fan motor is rated at 100 cfm. The thing is that the fan does not seem to be working any better with the new motor because the bathroom mirror is still steamed up after I take a shower. After replacing the fan motor I could feel air being forced down into the bathroom along the edge of the mounting plate for the fan. I put a piece of tissue up to the fan and the tissue stays on the fan cover plate. I donot understand why the bathroom mirror stays fogged up after a shower. It would seem that a 100cfm fan would be more tha enough to handle a 36 square foot bathroom. The exhaust fan is located in the ceiling right next to the shower stall. Any help would be greatly appreciated. I did check the fan flapper and it seems not to be binding and opening when the fan motor is turned on.

I have the same situation and it doesn't bother me; I just wipe the mirror off. We have a window in our bathroom and the extra air should help but doesn't. So go figure and live with it. Why does it bother you ?

The fan is working, but you are making more cubic feet of steam than the fan can handle. Since the steam diffuses around the room, it all cannot all go up the vent instantly. What doesn't go up condenses on the mirror because the glass is colder than the moist air in front of it.
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I bet you could install some sort of mirror heater, but my wife has the right idea. She uses the hairdryer to blow warm air against the glass before she uses it on her hair.

Ahbplus, it wasn't intended to be a professional answer. There are some answers here, some opinions, some very professional answers. Mine was intended as an opinion.

ms. tickle

Duce432,
Is the door to the bath open or closed? The fan can't remove any air from the bath unless other air can come into the room.

Harold's entirely correct. You must have air movement throughout the bathroom to remove the moisture. The moisture will be worse in the winter time as in warmer weather the AC will be on to pull the noisture out quicker.
Hope this helps, Tom