Most People don’t have a clue how long it takes a fan to remove all that moist air you’re creating every time you have a shower. They towel off, brush their teeth or shave, and flip off the fan when they leave the bathroom. I’ve heard experts say the exhaust fan needs to run for at least 20 minutes after you’re finished you shower, but I recommend 30 minutes just to be safe. And make sure you crack the door or a window open while the fan runs. If the bathroom is sealed, it restricts airflow and your fan can’t push warm air outside. Installing a timer makes it easier. This preventive measure helps control moisture and can add years to the life of your bathroom.