How to Install Bath Fans

A typical bath fan.

A bath fan is installed to vent moist air outside so it doesn’t build up in the bathroom, where it could contribute to the growth of mold and mildew. Some bath fan units are made to be installed in the ceiling, in place of existing ceiling light fixtures. The fan is then controlled by the same wall switch that controlled the light. For this configuration, it’s necessary to have a bathroom with an unfinished attic above it.

Things You'll Need

• Screw gun
• Bath fan kit
• Pencil
• Jigsaw
• Wire nuts
• Electrical tape

Instructions

1. Turn off the electricity to the existing ceiling fixture, at the house circuit box. Remove the existing fixture by unscrewing the screws holding it to the ceiling electrical box and pulling apart the wires.

2. Locate the electrical box on the floor of the attic above the bathroom. Disconnect the bundle of wires that are feeding into it (there will usually be a wire clamp that you can unscrew), and set the wires aside, with the other end still attached to the house system. Unscrew the electrical box from the joists that it’s attached to, revealing the open hole leading down to the bathroom below.

3. Lay the bath fan unit on the attic floor covering the hole with the intake vent of the fan. Use a pencil to trace around the edge of the vent. Take the unit away and cut out the floor and ceiling below it along the traced line.

4. Drop the intake vent of the fan unit in the hole, with the rest of the unit sitting on the attic floor. Attach the unit to the two closest joists on either side, securing the brackets on the sides of the unit to the joists with the screws that came with the fan.

5. Install the bath fan’s exhaust hose, connecting it to the fan unit according to the instructions (they will vary for different units) and pulling the other end to the nearest external wall. Mark the shape of the end of the hose on the wall and cut it out with the jigsaw. Secure the hose over the hole with the screws that came with the fan. Go outside and install the vent cover over the outside of the hole, using the provided screws.

6. Return to the attic. Connect the wires from the old fixture to the new unit using wire nuts. There should be one black and one white wire coming out of the unit, and the same colored wires from the house, in addition to a bare copper ground wire from the house. Twist the wire nuts around the two black wires, then the two white wires. Wrap the ground wire around the green screw and tighten it.

7. Return to the bathroom. Set the ceiling vent cover in place over the hole in the ceiling, attaching it to the fan unit with the built-in wire hooks on the vent. Turn on the power and test the fan unit at the wall switch.

References

• This Old House: Bathroom Exhaust Fan Installation.