Which of the following factors is essential for duct size calculations?

The factor that is essential for duct size calculations is CFM, which stands for cubic feet per minute. CFM measures the airflow rate through the duct system and is crucial for determining the appropriate size of the ducts needed to distribute air effectively within a building.

When calculating duct sizes, it's important to match the CFM requirements of the HVAC system with the duct's ability to supply enough air to each room. If the ducts are too small, they can restrict airflow, leading to inefficiencies in heating or cooling and potentially causing increased energy usage. Conversely, if ducts are too large, it can result in excessive airflow and wasted energy.

While temperature, humidity, and static pressure are important factors in an HVAC system, they influence system performance and comfort rather than directly determining duct size. Temperature and humidity affect the nature of the air being moved, while static pressure relates to the resistance encountered by the airflow, but CFM is the primary measurement used specifically for sizing ducts.