Fiberglass Duct Board (Duct Board):
Typically installed where insulated ductwork is required, providing better thermal performance compared to metal ducts in some applications.
Duct board's R-Value is 4.3 per inch of thickness, offering high insulation value.
Although it has a lower fire rating than metal ducts, its advantages include noise reduction and ease of sealing to minimize air leakage.
Newer versions are coated with antimicrobials to resist mold growth, though they shouldn't be installed in high-humidity or wet areas due to mildew risks.
Duct Board Fabrication:
Shipped in 4x8 or 4x10 foot sheets and easily fabricated on-site using duct knives.
Knife Options: Shiplap or V-groove knives are used to cut grooves for folding into a rectangular duct.
Duct boards require only a few tools for cutting, measuring, and sealing, making them lightweight and easy for one person to install.
Airflow and Pressure:
Air resistance in ducts is measured in inches of water column (inch WC).
Duct board can handle up to 24-inch supply ducts and 22-inch return ducts without additional reinforcement.
Support and Installation:
Duct board can be laid directly on ceiling joists or roof trusses in attic spaces, or suspended with support every four feet.
The duct can be supported with 2-inch wide nylon webbing or metal strips.
When transitioning duct sizes, gradual size changes are necessary on supply ducts to avoid turbulence, typically requiring a 12-inch-long transition fitting.
Considerations:
The duct board wall thickness (1 to 2 inches) must be accounted for when preparing hangers or cutting holes for ducts to pass through.
A hole for a 20x8 inch duct, for example, must be at least 22x8 inches.
Branch Run Installation:
Branch run holes should be cut before hanging the duct. A fiberglass duct board hole cutter can make perfect circles.
After the duct is hung, takeoffs like long-tab or spinning takeoffs are used to connect branch ducts, usually flex ducts.
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