What is the proper way to vent a clothes dryer?
Here are some facts from the United States Fire Administration.
Dryer exhaust should vent directly outside the home. In some new homes, washers and dryers are placed in non traditional areas of the house, including upstairs bedrooms, hallways and closets. These new sites generally require longer dryer vents in order to reach an outside wall and may contain sharp turns and bends that snake through the home.
Dryer vents should not be longer than the equivalent of 25 feet ( five feet is added to the actual vent length for each 90 degree bend in the vent).
When lint has to pass through an exhaust that is under a floor or through walls and is more than 6 feet long, it is almost impossible for all the lint to be propelled out of the vent.
Lint can also accumulate in pockets along the vent where it is harder to reach and clean.
Smooth walled metal duct is the best choice. In fact, almost all manufacturers now state in their manuals not to use plastic flexible dryer ducts between the vent and the clothes dryer. Many existing homes as well as some new construction, continue to use plastic flexible ducts. The plastic itself can provide additional fuel for a fire. Even flexible foil vents are not the best choice for venting clothes dryers. Flexible vents can sag, allowing lint to build up and catch fire if it comes in contact with a sufficient amount of heat. If a fire starts beneath the dryer when the motor overheats, then the drafts from the dryer can pull that fire up into the duct and venting, allowing a house fire to develop.
To avoid problems, make sure you disconnect, clean and inspect the dryer and venting at least once a year, or hire a professional company to clean the dryer components.