Turn off the power on the circuit breaker to the electricity in the bathroom. Use the template that comes with the unit to trace the shape you need to cut on the ceiling where the electrician has installed the wiring between the ceiling joists. Use a small jigsaw with a drywall blade or a drywall saw to cut the hole. To prevent cutting any wires, make the cut as shallow as possible. If the fan is already installed, be sure your cuts don’t disturb the unit or ducts attached to it.
Attach the electrical box supports to the most conveniently located joist with the screws provided with the box, ensuring the box is deep enough in the ceiling to leave room for the housing of the light fixture. The number of joists and screws needed to secure the box depends on the size of the fixture.
Before connecting the wiring, study the manufacturer’s diagrams and instructions to determine which color wires go where. Most units advise connecting the white fixture wire to the white house wire and connecting the remaining two red wires. If you are attaching the light to an existing fan or are unfamiliar with electrical wiring connection techniques, have a licensed electrician install the wiring.
After the wires are connected, line up the holes in the housing with the holes in the body of the light fixture and securely screw them into place. Install a light bulb into the recessed light with the wattage recommended by the manufacturer. Cover the light with the moisture-resistant cover supplied with the light. The cover may snap into place or require screws to keep it in place.
If the existing fan in the bathroom is several years old, it may be more practical to install a fan-light combination unit so you don’t have to remove the light to replace the fan in the future. Consult your local building code to determine if a ground fault circuit interrupter (GFCI) outlet is required for the light fixture and fan.