This Old House host Kevin O'Connor works with electrician Brian Bergeron to install a ventilation fan in a bathroom
1. Turn off the electrical power to the circuit you'll be working on.
2. Disconnect the existing wall switch and trace the outline of a new metal switch box onto the wall.
3. Use a drywall saw to cut through the wall, expanding the switch-box hole.
4. Remove one side from the existing metal switch box, then remove one side from the new metal switch box.
5. From inside the attic, drill 5/8-inch hole down through top wall plate directly above the switch box.
6. Attach end of nonmetallic electrical cable to the fish tape, then feed tape down the hole to the switch-box location. Use the tape to pull the cable from the attic to the switch box.
7. Secure the cable to the new box with a cable connector. Tighten green grounding wire to grounding screw inside of box.
8. Slip new switch box into the wall and screw it to the old switch box.
9. Connect the wires on the new fan control (switch) to the cable; screw the control to the box.
10. Set fan between two ceiling joists, then use a hammer and screwdriver to tap holes through the ceiling alongside the joist.
11. Hold the fan against the ceiling and trace around it. Cut the ceiling hole with a drywall saw.
12. Screw the fan to ceiling joists from below.
13. Connect the electrical cable to the fan motor, then replace the cover plate.
14. Attach a 90-degree elbow to the exhaust port on the side of the fan.
15. Connect a flexible duct to the elbow; secure all connections with duct tape.
16. Drill a 3/8-inch pilot hole through the sidewall of the attic, then move outside and cut the vent hole using a 4-inch-diameter hole saw.
17. Apply silicone caulk around the vent's flange, then screw the vent to the house.
18. Snap a grille over the vent.
19. From inside the attic, connect the flexible duct to the sidewall vent.
20. Replace the attic insulation around the fan.
21. Install the ceiling grille to the fan.
22. Turn electrical power back on and test fan.