How to Vent a First-Floor Bath

Shut off the electricity to the bathroom at the house’s electrical panel. Drill a hole in the ceiling where you plan to install the bathroom fan, and where a closet is located directly above the bathroom, stopping once the drill penetrates the floor above. Go into the room above the bathroom to see exactly where the drill penetrated, and to adjust the positioning of the fan, if necessary.

Hold the bathroom vent against the ceiling, with the exhaust opening against the hole you drilled. Trace around the perimeter of the fan housing on the ceiling. Remove the fan and cut along the line you traced, using a drywall saw, and remove the drywall.

Cut a hole in the floor above where the drill bit penetrated, using a hole-saw attachment on your drill. The attachment needs to be slightly larger than the duct you plan to connect to the fan’s exhaust port.

Pull the electrical wiring in the subfloor above the bathroom ceiling through the electrical knockout on the side of the fan assembly. Strip 6 inches of the wiring’s insulation off, and then twist the same colored wires from the ceiling wire and the wires in the assembly together. Twist wire nuts onto the wires to hold the connections together, and then tighten the screws where the electrical wiring enters the fan assembly, holding it in place.

Hold the fan assembly inside the cutout you made in the ceiling, while a helper reaches through the hole in the floor above and pulls out the brackets on the sides of the fan assembly until they touch the floor joists. The helper then must drive screws through the ends of the brackets and into the floor joists.

Insert a 6-inch-long metal duct piece into the cutout in the floor and over the exhaust port in the fan assembly. Drive sheet metal screws through the sides of the duct and into the exhaust port’s lip. Dangle a plumb bob from the ceiling above the duct until the plumb bob dangles over the center of the duct opening, and then mark the location of the plumb bob on the ceiling.

Cut a hole in the ceiling with the hole-saw attachment, with the mark you made on the ceiling in the middle of the hole saw. Climb into the attic through the attic-access panel, and lower a second length of metal ducting through the hole in the ceiling. Drive sheet-metal screws through the sides of the new duct piece and into the smaller duct piece, and then wrap foil duct tape around the connection.

Insert a flexible duct over the end of the duct inside the attic and slide an insulation sleeve over the duct. Tighten a hose clamp over the duct, flexible duct and insulation sleeve to secure the connection. Drive a 3-inch wood screw through the roof, from inside the attic, marking where you plan to vent the duct through the roof.

Climb onto the roof using a ladder and locate the screw coming through the roof. Hold the roof cap’s duct piece on the roof, with the screw in the middle, and cut around the perimeter of the duct with a utility knife. Remove the cut shingles, and then cut through the roof with a jigsaw, following the same cut line as the shingles.

Insert the duct piece for the roof cap in the hole, and then drive sheet-metal screws through the sides of the duct and into the roof. Insert the cap over the duct, and cut away any shingles that contact the hood, using the utility knife. Pick up the shingles above the cap and insert the flange below the shingles, and then apply roofing cement to the flange to attach the shingles.

Drive roofing nails through the exposed edges of the cap’s flange. Go back in the attic and attach the flexible duct to the duct piece in the roof using the hose clamp. Restore the electricity to the bathroom, using the electrical panel.