Proper Ductwork for a Bathroom Fan

Plan the location of the bathroom fan. The ductwork from the bathroom fan needs to extend to the exterior of the house through a wall or the roof. If the bathroom is on the main floor of the home, with an attic space above, the fan could be located anywhere in the ceiling of the bathroom. If a living space is located above the bathroom, the fan needs to be placed between joists where the ductwork can access an exterior wall.

Connect the ductwork to the outlet of the bathroom fan assembly. Flexible ductwork is commonly used. This is the same duct material used for dryer vents. Place the ductwork between the ceiling joists from the bathroom fan assembly to the nearest exterior wall. For roof vents, the ductwork extends up from the bathroom fan to the roof of the home.

Install the exterior vent cover. Drill a hole through the wall or roof from the inside at the planned center of the vent opening. Cut a 4-inch-round opening around the center point established by the drilled hole. Cut away the shingles on the roof before cutting the roof sheathing with a reciprocating saw. Also use a reciprocating saw to cut wall materials.

Fit the vent hood through the wall or roof hole. Roof vents have covers to prevent rain or snow infiltration, while wall vents may have louvers or other weatherproofing features. Fit the shingles around the roof vent and seal with roofing tar. Fit the wall vent to the hole and caulk around the vent.

Connect the flexible ductwork to the interior of the wall or roof vent. Place insulation around the ductwork and the interior of the roof or wall vent.