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How to Vent a Clothes Dryer

Ask This Old House plumbing and heating expert Richard Trethewey travels to Cleveland to reroute a lengthy dryer vent.

Steps for Venting a Clothes Dryer

  1. Measure and mark the correct location for the rigid pipe to vent to the outside.
  2. Drill a pilot hole through the marked location to determine where to drill from outside.
  3. When drilling through vinyl siding, set the drill into reverse and lightly score the hole based on the center of the pilot hole using the hole saw.
  4. Set the drill into the correct direction and drill the hole. Don’t cut all the way through to the other side.
  5. Go back inside and drill the rest of the hole from the inside. This will ensure the cut appears clean on both sides of the hole.
  6. Measure and cut the rigid vent pipes to size. Seal the seams of the vent pipes with the duct tape.
  7. Insert the pipe into the dryer vent cover. Seal the seam with more duct tape.
  8. From the outside, insert the pipe into the hole. Secure the vent cover to the exterior wall with screws. You can add an additional critter cover over the dryer vent cover to prevent pests from coming in.
  9. Insert the other end of the pipe into a dryer vent elbow and seal it with duct tape.
  10. Push the dryer back into position. Connect the dryer vent to the elbow and secure it using a clamp and a screwdriver.
  11. Plug the dryer back in.

Resources:

Richard recommends keeping the dryer vents as short as possible to prevent lint from accumulating and clogging the vent. All of the pieces Richard used to install the vent, including the duct tape, the rigid pipe, elbows, and the duct cover are available at home centers.


Q: Previous owners moved the laundry room to the second floor and terminated the dryer vent in the attic space above, since it’s not near an exterior wall. What’s the best way to vent it to the outside?

Fall 2021 Ask TOH, Richard Trethewey
Richard uses a pair of straight-cut tin snips to slice through this steel dryer duct.
Colleen McQuaid

A: It’s become popular to put laundry rooms on the second floor for the convenience, but venting a clothes dryer into an attic is a big mistake. Warm, moist air from the vent creates a perfect climate for mold to grow on the roof framing, sheathing, and anything you’ve stored in the space. In cooler weather, that damp air will condense on cold surfaces, soaking insulation and possibly damaging the ceiling below. And in snowy climates, all that extra warmth contributes to the formation of ice dams.

To avoid these problems, consider the most direct route to the outside—through the roof. In that case, you’ll need to connect the ductwork to a hooded roof vent that offers minimal resistance to airflow from the dryer.

Installing such a vent, even on an asphalt-shingled roof with a low slope, is best left to a roofing pro with proper fall-protection equipment and who knows how to properly flash around roof penetrations. Once the vent is installed in the roof, you can connect it to the dryer duct from inside the attic. Seal the connection to the vent, and any seams in the duct, with foil tape. Make sure to seal around the duct where it comes into the attic using a fire-stop sealant such as Fire Barrier CP 25WB+ made by 3M. Then wrap the metal with R-8 duct insulation to minimize internal condensation.

You also might be able to run the duct to an exhaust vent on an outside wall at least 3 feet from a window or door. Dryers can operate with straight duct runs as long as 35 feet, but you have to subtract 5 feet from the run for every 90-degree turn the duct takes. If the dryer is still within reach of an outside wall, then have a handyman cut a hole for the duct and connect it to the vent. Whichever direction your duct goes, only use the kind made with 4-inch galvanized steel. Its smooth walls ensure good airflow, keep lint buildup to a minimum, and are fire resistant. The lint-trapping corrugations in flexible plastic or foil-faced flexible ducts are a fire hazard, and slow down airflow, which adds to drying time, and forces the dryer motor to work harder.


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