How to Wire a Ventilation Fan & Light
By Chris Deziel
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The warm temperatures and high humidity in a bathroom create ideal growing conditions for mold, and they also deteriorate wooden and metal fixtures. You can keep humidity down by installing a ventilation fan. To be effective, the fan should be more or less centered in the ceiling, which is also a good place for a light, so many fans come with a light fixture. You often have the option of wiring the fan and light to separate switches, but you can also choose to use the same switch so that they come on at the same time.
Cut a hole for the electrical box for the switch in the drywall near the door or in some other convenient location, using a drywall saw. Use a remodeling box for the switch. It anchors directly to the drywall so you don't have to worry about attaching it to a stud.
Pull electrical cable between the fan/light and the switch. If the fan has a pair of black wires and a pair of white ones, you can wire the light separately from the fan. If you choose to do this, pull 3-conductor cable, with a white, black, red and bare wire. Otherwise, use 2-conductor cable, which doesn't have a red wire.
Connect the fan and light to the cable. If there is only one hot wire, twist it together with the black cable from the switch with pliers. If there are two hot wires, and you want the switch and light to be operated by the same switch, twist both of them together with the black wire.
Use the red wire in the 3-conductor cable to put the light and fan on different switches. Connect the hot wire from the fan to the black wire from the switch and the hot wire from the light to the red wire from the switch. The hot wires in the unit may be colored differently. If so, check the installation instructions to determine which is which.
Twist all the white wires together, and then twist together all the bare wires. Cap each wire set with a screw-on wire connector.
Feed a circuit cable into the switch box after first making sure the power to the circuit is off. Strip all the the cables in the box with a utility knife, and expose all the wire ends with wire strippers.
Wire the hot circuit wire to the top brass terminal of a switch. If you are using two switches, use a short length of black wire to join their top terminals so they'll both be hot when you connect the circuit wire to one of them. Connect the hot wire from the fan to the bottom terminal of the switch. If there are two hot wires, connect one to the bottom terminal of each switch.
Splice all the white wires in the box together, twisting them clockwise with pliers, and screw on a wire connector. Twist together all the ground wires, and join the end of one to the green ground terminal on the switch.
Screw the switch onto the box with a screwdriver, and screw on a cover plate to finish the wiring procedure.
Lowe's: Install a Bathroom Exhaust Fan
Electrical Online: Wiring a Light Switch
To pull the wire between the fixture and the switch, run it through the attic to the wall on which the switch is located, drill a 1/2-inch hole in the top plate of the wall, and feed the wire through the hole to the switch.
Do not do any wiring until you're sure the power is off. If you aren't sure, test the wires in the circuit cable with a voltage tester. Keep turning off breakers until you get a reading of 0, or the light stays off.
Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.
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How to Wire a Three-Way Wall Switch
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How to Wire an Existing Overhead Light to a New Wall Switch
How to Install a Switch on an Outdoor Light Post
How to Wire a Ceiling Fan to an Existing Outlet Wire
How to Wire a Timer Switch with No Neutral Connection
How to Install Switch Controlled Light Fixtures
How to Make Electrical Connections for a Ceiling Fan
1 How to Know When to Replace a Dryer Filter
2 How to Wire a Three-Way Wall Switch
3 Leviton Three-Way Switch Replacement
4 How to Wire an Existing Overhead Light to a New Wall Switch