In Manual D, what is the suggested friction (IWC) loss for hand dampers?

In Manual D, which is a guideline for the design of residential duct systems, the suggested friction loss for hand dampers is typically set at 0.03 inches of water column (IWC). This standard is based on the need for minimizing resistance in the airflow while allowing for effective control of the air distribution in a duct system.

Hand dampers are devices used to manually adjust the airflow within a duct, and it’s essential for these dampers to have a low-pressure drop to ensure that they do not create significant back pressure or hinder system performance. The 0.03 IWC value provides a practical balance between control and efficiency, helping maintain a consistent and effective airflow throughout the system.

Using this figure helps HVAC professionals to design systems that are both responsive and efficient, ensuring that air reaches its designated locations without excessive energy loss. The other suggested friction loss values are not aligned with the standards outlined in Manual D for hand dampers, which emphasizes the importance of using the correct specifications in design to achieve optimal system performance.