Does the lint that passes through the duct just go straight outside?
Some of it does make it outside, but a considerable amount of lint sticks to the inside of your duct, especially if there are bends in the duct pipe. The dryer’s exhaust air cools as it travels through the duct, causing moisture to condense on the interior surfaces of the duct. Lint and other debris in the exhaust air sticks to the moist surface and builds up over time. Eventually, the buildup reduces required airflow, which in turn accelerates the buildup of lint.
