A ventilation fan for a bathroom typically is wired to a standard lighting/receptacle circuit. Depending on the model, the fan may be controlled by a regular, single-pole wall switch or a timer switch. Some fans include a built-in humidistat switch that automatically turns the fan off when the room air is sufficiently dry. Contact the fan manufacturer to learn about compatible switch options for your model. In a standard installation, a vent fan is connected to the switch with the fan at the end of the cable run, just as with standard light fixture wiring.
Turn off the power to the circuit cable feeding the electrical box for the wall switch at the home’s service panel (breaker box).
Install the fan housing to the ceiling framing, following the manufacturer’s instructions.
Run 14-gauge, 2-wire, non-metallic cable (14/2 NM) from the fan housing to the electrical box for the switch; this is the “fan cable.” Secure the cable every 4 1/2 feet and within 12 inches of the fan housing and electrical box (or as directed by the local building code), using insulated cable staples.
Connect the switch to the source cable and fan cable, following the switch manufacturer’s wiring diagram. Mount the switch to the electrical box, and install the cover plate.
Install the fan’s motor unit, as applicable. (Some fans come with the motor pre-installed.) Connect the fan cable to the motor unit as directed by the manufacturer. Most fans have two wire leads that connect to the matching black and white cable wires with wire nuts (plastic wire connectors), plus a ground screw for connecting the cable’s ground wire to the fan housing.
Complete the fan installation (running duct, installing vent cap, attaching grille) as directed. Restore power to the source circuit, and test the fan operation.
All electrical installations must conform to the local building code. Consult your city’s building department for recommendations and applicable code requirements.