What is the primary use of Manual D?

The primary use of Manual D is to size the ducts in a heating, ventilation, and air conditioning (HVAC) system. This manual provides guidelines and methods for determining the appropriate duct dimensions needed to ensure optimal airflow and system efficiency. Proper duct sizing is crucial for maintaining comfort levels within a building, as it directly affects the delivery of conditioned air to each room. By adhering to the criteria outlined in Manual D, professionals can avoid issues like insufficient airflow or excessive noise, which can arise from improperly sized ducts.

While the other options involve important aspects of HVAC systems, they are not the main focus of Manual D. Sizing heating equipment is typically addressed in Manual J. Evaluating air quality involves other assessments that focus on indoor environmental conditions, and calculating energy costs pertains more to financial considerations rather than the physical sizing of ducts. Thus, Manual D's specific purpose in defining duct sizes distinguishes it from these other functions.