A Dryer Vent Explained

A dryer vent exhausts hot, moist, linty air (and resultant gasses of combustion if it is a natural gas dryer) from the dryer to the outside of the house. Although I've seen dryers vent into crawl spaces, attics, joist cavities, or just straight into their own laundry room, none of these scenarios are permissible. The dryer must vent to the exterior.

To create the dryer vent, a route must be established from the dryer to either the roof or exterior wall that is within the overall length guidelines and also is able to be efficiently routed. This dryer vent system is comprised of several items:

• Transition duct -- should be rigid metal or semi-rigid metal. This is the duct that connect from the dryer to the main duct.
• Main duct -- should only be heavy gauge rigid duct. This is the duct that connects from the laundry room to the exterior.
• Insulation -- wrapped fiberglass. This is recommended for ductwork in unconditioned spaces.
• Termination hood -- ideally metal without a pest guard. This is what the duct connects to and interacts with the outside world. It's what you see of the dryer vent system from the exterior and it is the actual point where the exhaust leaves the dryer vent.

As the exhaust travels through the dryer vent system, the moisture condenses on the inner wall of the duct. The condensed moisture then pulls the lint out of the exhaust and causes it to accumulate. As this happens, the airway slowly chokes down in size (1/2" of inner wall accumulation restricts the duct by almost 50%). Also, as the velocity of the exhaust stream dissipates over the distance of the ductwork, then further accumulation occurs.

I hope these basic help you understand your house's dryer vent better.