Most of us don’t pay attention to the fan in our bathroom ceiling until it fails and starts making noise, but the bathroom fan plays a very important part in keeping moisture out of your bathroom. An improperly installed bathroom fan can do more harm than good.
You should check the fan for dust build-up which can hinder airflow
If you have insufficient ventilation in your bathroom you might notice moisture stains, mold, peeling wallpaper or high levels of humidity.
The duct for the exhaust must terminate outdoors, and not anywhere inside the building. If not, you might experience problems with condensation and mold where the warm, moist air meets cold building materials.
Condensation from fan exhaust can also reduce the effectiveness of your insulation material.
The ducts themselves must also be made from the correct materials to ensure proper airflow.
The termination to outside the house also needs to be shielded from rodent entry into the house.