HVAC Ductwork Systems Flashcards

What is the standard duct sealant class designation system used in SMACNA?

Answer: Seal Class A (all seams and joints), B (transverse joints and seams), and C (transverse joints only)

SMACNA defines Seal Class A (most stringent — all seams, joints, and wall penetrations), B (transverse joints and seams), and C (least stringent — transverse joints only). Higher-pressure systems require more sealing.

What is a 'take-off' fitting in HVAC ductwork?

Answer: A branch connection fitting that diverts a portion of airflow from a main duct to a branch duct

A take-off is a branch fitting that connects a smaller branch duct to a larger main duct, diverting a portion of the airflow. Common types include conical, straight, and 45-degree take-offs.

What is the recommended hanger spacing for rectangular ductwork up to 48 inches wide?

Answer: Every 8 to 10 feet maximum

SMACNA recommends maximum hanger spacing of 8 to 10 feet for rectangular duct up to 48 inches wide. Larger or heavier ducts require closer spacing and stronger hanger materials.

What is the purpose of a 'volume damper' versus a 'splitter damper' in a duct system?

Answer: A volume damper restricts total airflow in a single duct, while a splitter damper divides airflow between two branches

Volume dampers (butterfly or opposed blade) regulate total airflow through a single duct section. Splitter dampers are positioned at branch take-offs to proportionally divide airflow between the main and branch ducts.

What is the effect of a duct system having too many sharp 90-degree elbows?

Answer: Increased pressure drop, reduced airflow, higher energy costs, and potential noise problems

Sharp 90-degree elbows create significant turbulence and pressure drop. Each adds equivalent length to the system, reducing total airflow capacity, increasing fan energy consumption, and generating noise.

What is the ASHRAE recommended outdoor air ventilation rate for general office space?

Answer: 15 to 20 CFM per person

ASHRAE Standard 62.1 recommends approximately 15 to 20 CFM of outdoor air per person for general office space. This provides adequate dilution ventilation for acceptable indoor air quality.