Depending on the pressure class of the duct, there will be a corresponding seal class (#2) from c to a. All return, relief and outside air ductwork located upstream of the air handling unit or between the return fan and the ahu should be sealed in accordance with seal class a or b, depending on the operating pressure specified Defined as joining of two longitudinally (in the direction of airflow) oriented edges of duct surface material occurring between two joints
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Duct sealing, air leakage criteria, and air leakage tests
Ducts shall be sealed as per duct sealing requirements of smacna hvac air duct leakage test manual for duct pressure classes shown on the drawings.
But smacna also states that “the designer is responsible for determining the pressure class or classes required for duct construction and for evaluating the amount of sealing necessary” Smacna breaks down the sealing of commercial ductwork into three classes Understanding the different classes in ductwork based on smacna standards is essential for hvac professionals and contractors to select the appropriate type of ductwork for specific. 1) the document outlines duct sealing requirements for different duct construction classes based on applicable static pressure
Class a requires sealing of all transverse joints, longitudinal seams, and duct wall penetrations Class b requires sealing of all transverse joints and longitudinal seams Class c requires sealing of only transverse.
