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# Ductwork - Seal Classes

## Ductwork air leakage classes.

ASHRAE and SMACNA standards specify the duct sealing requirements in terms of seal classes A, B and C.

• Seal Class A - All transverse joints and longitudinal seams and duct wall penetrations shall be sealed. Pressure sensitive tape shall not be used as primary sealant. Max. 2 to 5 percent total system leakage.
• Seal Class B - All transverse joints and longitudinal seams shall be sealed. Pressure sensitive tape shall not be used as primary sealant. Max. 3 to 10 percent total system leakage.
• Seal Class C - All transverse joints shall be sealed. Max. 5 to 20 percent total system leakage.
• Unsealed - 10 to 40 percent total system leakage.

## Related Topics

• ### Ventilation

Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

## Related Documents

• ### Air Duct Components - Minor Dynamic Loss Coefficients

Minor loss (pressure or head loss) coefficients for air duct components.
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A major friction loss diagram for air ducts - Imperial units ranging 10 - 100 000 cfm.
• ### Air Ducts - Major Friction Head Loss, Online Calculator

Head loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - Imperial and SI units.
• ### Duct Velocity

Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator.
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Thickness of sheet metal used in ductwork.
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Recommended distance between ductwork support hangers.
• ### Equivalent Diameter - Rectangular vs. Circular HVAC Ducts

Rectangular equivalent diameter for air flows between 100 - 50000 cfm.
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Recommended air velocities in HVAC ducts.
• ### Noise generated in Air Ducts

Estimate noise generated by air flow in ducts.

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## Citation

• The Engineering ToolBox (2019). Ductwork - Seal Classes . [online] Available at: https://www.engineeringtoolbox.com/ductwork-seal-classes-d_2152.html [Accessed Day Month Year].

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