Which factor is most significant in determining duct size?

The required airflow rate is crucial in determining duct size because it directly influences how much air needs to be transported to achieve the desired heating or cooling capacity in a space. Properly sized ducts ensure that the HVAC system operates efficiently while providing adequate air distribution throughout the building.

When the airflow rate, measured in cubic feet per minute (CFM), is identified based on the heating and cooling load calculations for the space, it dictates the size of the ducts required to transport that amount of air. If the ducts are too small, the system will struggle to deliver the necessary air volume, leading to decreased efficiency and comfort levels. On the other hand, oversized ducts can lead to increased material costs and may affect system performance and air quality.

While factors like the length of duct runs, type of insulation, and location of the HVAC system can impact other aspects of ductwork design, they do not fundamentally determine the required duct size as directly as the specified airflow rate does. Understanding the airflow needs is essential for ensuring that the HVAC system functions effectively and delivers the desired thermal comfort.