How to Install a Bathroom Exhaust Fan

When you step out of the shower are the walls and other bathroom surfaces covered with condensation? Over time, this moisture and humidity can make paint begin to peel, cabinets and doors can warp and even mold can start to prosper in corners. You can relieve this buildup of moisture in your bathroom by installing an exhaust fan. Keep reading to find out how.

  • Step 1: Mark Fan Location

    Decide where on the ceiling your new exhaust fan will be located. Many exhaust fan models also double as a ceiling fixture, but you don’t have to remove your current ceiling light fixture if you love it. Your fan will most likely be adjacent to the current fixture though as it will require drawing power from the fixture’s wiring.

    If you’re not sure where your ceiling joists are, use a stud finder to determine their location and mark them lightly with a pencil. The exhaust fan unit will be anchored between two joists so they support the fan’s weight. Trace the dimensions of the fan unit on the ceiling with your pencil. Some models may come packaged with a template for marking the unit’s outline.

    Helpful Tip

    Read all manufacturer instructions carefully for your exhaust fan. The following instructions are a general how-to. Different fan models may have varying installation instructions.

  • Step 2: Cut Into the Ceiling

    Next you will need to cut a hole into the ceiling in which the fan will be placed. Before you begin, shut off power to the bathroom at the main electrical panel. If you’re unsure which circuit the bathroom light is on, you may need to turn off power to the whole house to be safe. You don’t want to be making blind cuts into the ceiling not knowing if there is electrical wire or other important structures located there.

    Safety Alert!

    Make sure the bathroom circuit is truly “dead” before touching any wiring or terminals. Check for a current with a high-voltage neon tester in one of the circuit’s electrical outlets. Be sure your tester is functioning by first trying it in a live receptacle.

    Use a drill to make starter holes in each corner of the marked outline and then use a drywall saw to cut the hole for the unit in the ceiling.

    Safety Alert!

    Wear safety glasses and a dust mask when cutting into the ceiling wallboard to avoid getting particles and dust in your eyes and respiratory system.

  • Step 3: Install Ventilation Duct

    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.

  • Step 4: Make Electrical Connections

    To connect power to the fan’s wiring, you’ll need to figure out which circuit to use to provide power to the fan. The simplest way is to take power from any available light fixture or outlet. Most likely this will be your ceiling light fixture.

    Remember, you also need to wire an extra switch to turn the fan on unless you want it to come on with the light all the time. You will need to run 3-wire cable between your new exhaust fan and the existing switch. Then you will need to remove the old switch and replace it with a double switch at that electrical box. Follow all manufacturer instructions carefully.

    Next, you will connect the exhaust fan wiring to the existing ceiling fixture wiring. Take a new piece of 12-2 electrical wire and join one end of it to the black and white wires of the fan unit by twisting the ends of each wire together. Use needle-nose pliers to twist wire ends together for the best connection. Connect the ground wire as instructed, if there is one, and then fasten the wire connections securely by twisting on wire connectors. Now connect the black and white wires at the other end of the cable to the corresponding wires on the light fixture.

    Helpful Tip

    All electrical work must be done in accordance with local codes. If you are not familiar with basic wiring procedures, you should hire a licensed electrician.

  • Step 5: Secure Fan Unit in Place

    Push all wiring into the hole, and then following the fan’s supplied instructions, attach the unit to the joists in the ceiling using the supplied hardware and a screwdriver. Snap the cover into place.

    Good job! Now you know how to install a bathroom exhaust fan, which can easily remove moisture and bad air from your bathroom with the flip of a switch.

Project Shopping List

Here’s what you’ll need to complete this project successfully.