Which of the following is not a factor in determining proper duct size?

The determination of proper duct size is fundamentally linked to several factors that directly influence airflow efficiency and system performance. Airflow requirement is crucial as it specifies the needed volume of air that the system must deliver, which dictates the size of the duct to ensure adequate supply without hindrance. The velocity of air plays a significant role as well; it helps in calculating the dimensions needed to maintain an efficient balance between airflow and pressure loss.

On the other hand, the temperature difference is not a primary factor when it comes to sizing ducts. While temperature can affect heating and cooling loads and may indirectly influence duct design by impacting overall system capacity, it does not directly determine the required physical dimensions of the duct itself. This stands in contrast to airflow and velocity, which are essential in the direct calculation of duct sizes for optimal system performance. Additionally, the material of the duct may influence aspects like insulation and durability but is not a critical component in the sizing determination process based on airflow dynamics.