A clothes dryer needs a clear airway to vent moist air from the drum as it tumbles clothes dry. Whether the dryer is gas or electric, there must be an exhaust vent to the outside to move the moist air. An improperly installed or poorly maintained exhaust vent increases dry time and is a fire hazard. It can also allow moisture to accumulate inside the duct, causing mold and fungus problems.
Dryer venting should be the shortest distance possible to get the most efficient dryer operation. International Mechanical Code article 504.6 states that appliance standards for dryer vents should be 25 feet or less of straight line vent between the dryer and the outside opening. For each 45 degree angle in the duct the maximum length should be decreased by 2.5 feet. For each 90 degree angle in the duct the maximum length should be decreased by 5 feet.
Lint accumulation is the most common venting problem. Signs that the dryer vent is clogged are long drying times, clothes that are still damp after the cycle, hot clothes at the end of the cycle, excess dryer noise, or the automatic sensors do not shut down the cycle.
Dryer vent ducts should be rigid metal with a smooth interior. The only part of the venting system that should be flexible is the connecting section between the back of the appliance and the duct opening in the wall.
Different types of dryer vent capping systems are available to use on the outside end of the vent. They are well insulated and they seal the duct when the dryer is not in use
Vent Problem Troubleshooting
Remove and clean the lint filter/trap between every load.
At least once a year, move the dryer away from the wall and clean the dryer vent/duct. Disconnect the flexible section from the back of the dryer. Use a long handled brush or vacuum cleaner attachment to reach inside the dryer shell and clean out lint.
Use a vacuum cleaner or vent brush to clean out the exhaust duct. Home centers carry a selection of dryer vent cleaning brushes. One type has a straight but somewhat flexible handle for straight ducts. Another type has an extendable flexible shaft that fits onto any power drill and rotates as it goes through the duct.
The flexible duct section can be cleaned and replaced, but the annual maintenance routine is a good time to simply replace it.
Flexible ribbed ducts are not acceptable for use with dryers. The plastic type is extremely flammable and will not withstand heat from the dryer. The metallic type also contains plastic. Neither can be cleaned with vent cleaning tools, and they trap and hold lint and moisture in the ribs.
Besides the common problems above, a clogged dryer vent can shorten the life of the dryer motor or bearings, and damage the heating element. The thermostat can also fail, causing the dryer to overheat or not heat at all.