The air and moisture that will be removed by the fan needs to vent outside. You will be installing a ventilation duct that connects the exhaust fan to a vent opening you will make in the exterior wall. Exhaust fans are also commonly vented through a roof soffit vent or a roof vent. This is sometimes not feasible depending on where your bathroom is located. Cutting a hole through the exterior wall specifically for venting the fan’s exhaust is the most direct way to vent the air and moisture outside.
Measure the outlet on the exhaust fan with a tape measure. If your fan kit did not include all materials, you will need this measurement to buy the correct size of flexible aluminum hosing to create your vent duct—the same type of hose that is used to vent clothes dryers. You also need these dimensions to know the required size of the vent opening you will be cutting in the exterior wall. Usually the hose is 4" in diameter. The correct dimensions may also be outlined in the manufacturer instructions. Look into the hole in the ceiling and locate the closest outside wall. Measure your wall height. Maneuver the hose into the ceiling hole until the other end is against the outside wall. Use a flashlight to assist you with visibility. Go outside to the other side of the bathroom wall and measure the same height up from where the floor would be in the bathroom to where the ceiling was. Add about 3" vertically and mark the location with a pencil. This is where you will be cutting into the wall. Making the hole can be done a couple of different ways. You can use the mark you made as the center of the hole and then use a combination of a drill and reciprocating saw, or you can use a 4" hole saw to create the opening.
Once you have the vent opening created, reach in and grab the vent hose, and pull it through the hole a few inches. Slide the hose over the stub of the vent wall cap and secure it with a metal clamp. Push the hose back into the hole and then secure the wall cap to the exterior wall with the supplied screws and a drill. Apply exterior silicone caulk with a caulking gun around the outer edge of the cap to create an airtight seal. Let the caulk dry for the time recommended by the manufacturer. Fasten the exhaust vent cover as directed in the vent instructions.
Back inside, be sure that the hose is lying flat against the ceiling inside the hole and trim off any excess hose with a utility knife. Connect the hosing to the exhaust fan outlet and secure it with a metal clamp.