How do I know if my dryer vent is clogged? Dryer duct cleaner Cape Coral. The first place to begin is by checking for airflow restriction. Some of the key indicators of a blocked or low airflow system are moisture buildup on the dryer door, lint buildup under the lint screen, and longer than usual drying times (45 minutes or more for most systems). So basically, if your dryer is taking more than 40 minutes to dry a load of clothes, you might need to have your vent system cleaned or possibly repaired.