Dryer vent pipes are available in various sizes with 4 inches, 4.375 inches and 4.5 inches being the most common sizes. All ducting for a dryer must be at least 4 inches in diameter, and the exit hole in the exterior wall is typically 4.25 inches wide.
Dryer vent piping should not exceed 25 to 35 feet in length, depending on the material used. For piping that includes a 90-degree bend, 5 feet should be deducted from the total. Dryer venting should not be connected to any other exhaust venting, and it should have a hood or roof cap equipped at the exterior of the home.