• In this video, This Old House general contractor Tom Silva explains how to vent a bathroom fan.


    1. Drive nail through house wall from attic; this will serve as a reference point for positioning the wall cap.
    2. From outside, use 4¼-inch hole saw to cut hole for wall cap.
    3. Apply caulk around the backside of the wall cap.
    4. Slide wall cap and connector duct into hole; secure cap with stainless steel screws.
    5. Wipe away excess caulk.
    6. In attic, seal holes in fan housing with foil duct tape.
    7. Use foil duct tape to attach flexible duct to connector protruding from the wall cap.
    8. Tape 90-degree elbow to opposite end of flexible duct.
    9. Screw elbow to outlet port on side of exhaust fan.
    10. Cut fiberglass insulation to fit tightly around fan housing.
    See products and services from this episode.
    • Difficulty: Easy to moderate
      Crawling around in the attic can be tough, but the rest of the installation is a breeze

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      Tools List

      • hammer
      • drill
      • caulk gun
        Caulking gun
      • keyhole saw
        4 ¼-inch-diameter hole saw

      Shopping List

      1. 16d nail, used as a reference point for drilling vent hole

      2. Wall-cap vent with 4-inch-diameter connector duct

      3. 1½-inch stainless steel screws, for attaching wall-cap vent

      4. Siliconized acrylic latex caulk, for sealing wall-cap vent 5. Cloth, for cleaning off caulk

      6. 4-inch-diameter flexible metal duct

      7. 4-inch-diameter sheet metal elbow

      8. Foil duct tape, for securing duct

      9. Self-tapping sheet metal screw, for attaching elbow to fan