of 4-inch duct, and subtract 5 feet for every 90-degree turn and 2 1/2 feet for every 45-degree turn for dryer vent installation. For example, a dryer with a 90-degree elbow at the exhaust port ...

Remember to include the duct run length and any elbows in your calculations. Adding an elbow connector or an external vent hood with a backdraft preventer will add approximately 10 to 15 feet of ...