How to Install Bathroom Fans Outside Your House

Bathroom ventilation fans that install on the exterior of your house are commonly known as wall-mount fans, because the motor unit is mounted onto an outside wall, where it is integrated with its own exhaust vent hood. A duct connects the motor unit to an intake housing installed between the joists above the bathroom ceiling. Wall-mount fans are commonly used when the bathroom is below upper-floor living space, which limits the options for duct runs and makes motor noise in the floor cavity (as you would have with a standard vent fan) undesirable. Installing a wall-mount fan is similar to adding a standard fan and duct system; it’s a reasonable do-it-yourself project that probably will take the better part of a day.

Stud finder or hammer and finish nail
Tape measure
Drill
4 3/8-inch hole saw
Drywall saw
Screws
4-inch vent duct
UL 181-approved foil duct tape

Instructions

- 1
  Turn off the power to the circuit that will supply the fan motor at the home’s service panel (breaker box). Use a stud finder or hammer and finish nail to locate the ceiling/floor joists to either side of the desired location for the intake unit. The vent duct must run straight out from the intake housing, along the joist cavity and out through the exterior wall.
- 2
  Measure the distance from the joist cavity to a window or other point common to both the interior and exterior. Transfer this dimension to the exterior side of the wall, and mark a point near the center of the joist cavity. At this point, drill a 4 3/8-inch-diameter (or as appropriate for the size of your duct/vent exhaust collar) hole through the exterior side of the wall and into the joist cavity, using a hole saw mounted on a standard drill.
- 3
  Cut a hole in the ceiling drywall that matches the diameter of the grille collar on the intake housing, using a drywall saw. If you don’t have access to the joist cavity from above, you may have to remove a portion of the ceiling drywall to gain access to the cavity for installing the vent duct and intake housing.
- 4
  Feed the electrical cable from the power source/wall switch to the motor unit. Apply caulk along the edge of the motor unit, and mount the unit to the exterior wall with screws.
- 5
  Install the intake housing as directed by the manufacturer; typically, the housing is mounted to the side of a joist or is secured between joists with suspension bars.
- 6
  Run 4-inch vent duct between the motor unit and the intake housing. Connect the duct to the collars on the motor unit and housing and secure it with UL 181-approved foil duct tape. Recommendations for duct materials and installation vary by manufacturer; follow the manufacturer’s directions and the requirements of the local building code.
- 7
  Complete the wiring connections at the motor unit and power source/wall switch, following the manufacturer’s wiring diagram.
- 8
  Install the intake grille over the ceiling collar on the intake housing, as directed. Restore power to the source circuit and test the fan operation.

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Ventilation