Venting the Fan
The best placing for the bathroom fan is somewhere between the shower and toilet. For the fan to operate at optimal efficiency, it should be no more than six feet from the sidewall where you will be venting the duct.
Before securing the fan to the ceiling joists, attach a 90-degree 4-inch elbow to the vent port, which is located on the side of the bathroom fan housing unit. Secure the elbow with screws and wrap the connection with foil duct tape. Most people use flexible duct because it’s easier to cut and work with, but galvanized steel pipe makes for a more durable job.
It’s essential that you get the venting right, or you could end up with water vapors condensing up in the vent. There are a diverse range of opinions in the remodeling community regarding the best way to vent a bathroom fan. But all experts agree that you should never vent the fan directly into the attic; that will only create moisture problems.
Vent the bathroom fan through the sidewall or the roof. Discuss your project with the local building inspector. Then, it might depend on your comfort level, especially working on the roof. Always follow the manufacturer’s guidelines for the product. Try to position the duct opening that keeps the duct as straight as possible. Turns and bends in the duct reduces the operation efficiency of the fan.
A horizontal installation, such as venting through a side wall, reduces the chance of condensation forming in the vent and rolling down the duct. When venting through a sidewall, position the exit on an exterior wall between two studs. Drill a test hole and stick something through the opening.
Locate the opening on the exterior; make sure that the duct exit won’t be obstructed. Determine if the emission of water vapors in the location will harm anything. Install a wall cap with a damper to keep out back drafts and insects.
If you vent through the roof, you’ll need a roof termination cap with a damper. You’ll need to make sure the roof cap is watertight after you install it.
Once you finalize the duct exit location, use a 4-inch hole saw to make your cut. Attach your cap on the wall or roof. Make any needed repair around the cap and make it watertight. Connect the cap to the duct; wrap all connections with foil duct tape. Insulate the duct with the special insulating product and tape only.