What type of duct configuration typically has lower airflow resistance?

Straight ducts are designed to minimize changes in direction, which is a primary factor that contributes to airflow resistance. When air flows through a straight duct, it encounters fewer obstructions and turns, allowing it to move more freely and efficiently. This results in a smoother airflow, which reduces turbulence and overall friction loss within the duct system.

In contrast, duct configurations like S-shaped, curved, and spiral ducts involve changes in direction or shape that can create disruptions in airflow. These configurations tend to increase resistance because they force the air to navigate bends and turns, leading to a greater likelihood of turbulence and pressure drop. Consequently, straight ducts are generally the most efficient in terms of airflow, making them the preferred choice when aiming to reduce airflow resistance in an HVAC system.