Installing a bathroom fan is the solution you need for spaces that never seem to get dry. Moisture-laden air is the enemy of bathroom paint, windows, doors, window sills, and fabrics such as towels and curtains. Expelling bathroom moisture and odors makes for a far more pleasant bathroom experience for all.
While bathroom exhaust fan installation is not the easiest home improvement project, the bulk of the work is centered around the physical rigors of standing on a ladder and working above your head, along with the more taxing work of crouching in your attic while wearing a dust mask or respirator. Aside from the physical work, bathroom vent fan installation is not difficult to understand, as it involves only one 120V power source and one run of flexible ducting that extends no more than 6 feet.
According to many building codes, bathroom exhaust fans are not required. A bathroom window that is at least 3 feet square in area and which opens halfway can substitute for exhaust fans in many municipalities. Section R303 of the International Residential Code discusses light and ventilation regulations. If you wish to use a window in place of a fan, verify this plan with your local permit office.
Before You Begin
Two issues often concern homeowners taking on this project: power and venting to the outside. Most residential bathroom fans use AC 120V electrical lines. These instructions offer tips for finding live electrical cables and running them to the correct location.
Venting means that after air from the bathroom is drawn into the exhaust fan, it is blown through a connected flexible duct and out of the house through a hole in the side of the house or roof. Since this is a new installation, not a replacement, your bathroom will not have ducts in place. However, as long as you can access the attic area above the bathroom ceiling, you will be able to route the flexible tubing outside.
Turn off the electricity to the existing ceiling light by flipping off the circuit breaker at the service panel. Locate your attic access door and enter it via the ladder, bringing your respirator and your portable light with you.
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Source: The Spruce