A dryer vent pipe is typically 4 inches in diameter and no more than 25 feet in length. The vent pipe connects the exhaust port on the dryer to a vent cap installed through the outside wall. Caulk seals the vent cap into the wall to prevent leakage and drafts.
The calculation to determine the appropriate length of vent pipe begins with 25 feet. Five feet is subtracted for each 90-degree elbow required, and 2.5 feet is subtracted for each 45-degree elbow required. This provides the minimum recommended length for the vent pipe. The installation of the shortest length that does not produce tension at the connection points to the dryer and vent cap simplifies the process of cleaning lint and debris from the vent pipe when necessary.