What is the nominal size diameter of domestic clothes dryer exhaust ducts?

The nominal size diameter of domestic clothes dryer exhaust ducts is typically 4 inches. This size is standard because it provides an adequate balance between airflow and the ability to effectively vent moisture and lint from the dryer to the outside. A 4-inch diameter duct helps ensure that the exhaust system can function efficiently, minimizing the risk of lint buildup and potential fire hazards while allowing for sufficient air circulation to facilitate drying.

Using a smaller diameter duct, such as 3 inches, could restrict airflow, leading to longer drying times and increased moisture levels. Larger diameters, like 5 or 6 inches, while they may seem beneficial in terms of airflow, would not be practical or necessary for most residential applications and could create complications with installation and space management. Therefore, the 4-inch size strikes an ideal balance and is thus recognized as the standard in most building codes and manufacturer guidelines for domestic clothes dryer exhaust ducts.