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# Ductwork - Seal 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

Design of 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.

### Air Ducts - Friction Loss Diagram

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.

### Ducts - Sheet Metal Gauges

Thickness of sheet metal used in ductwork.

### Ductwork - Supports

Recommended distance between ductwork support hangers.

### Equivalent Diameter - Rectangular vs. Circular HVAC Ducts

Rectangular equivalent diameter for air flows between 100 - 50000 cfm.

### HVAC Ducts - Air Velocities

Recommended air velocities in HVAC ducts.

### Noise generated in Air Ducts

Estimate noise generated by air flow in ducts.

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