Frequently Asked Questions

• What is the difference between duct board, a plenum, and a distribution (tri) box?

  Duct board is fiberglass sheet used to fabricate insulated ducts. A plenum is the supply or return transition box at the air handler. A distribution/tri box is a junction that splits airflow into multiple branches.

• Which thickness or R-value duct board should I choose for my climate or code requirements?

  Follow your local energy code and project specifications. Choose the board thickness and facing needed to meet the required R-value and vapor barrier details for your climate zone.

• Can these plenums and distribution boxes be used for both supply and return air?

  Yes. They are commonly used on both sides of the system when sized correctly and sealed with approved UL 181 closures. Ensure condensation control on supply components.

• What tools and accessories are needed to cut and assemble fiberglass duct board properly?

  Use sharp knives or V-groove tools, a straightedge/square, measuring tape, UL 181 tape and mastic, and a stapler or pins as required. Wear gloves, eye protection, long sleeves, and a dust mask or respirator.

• Are these products suitable for light commercial installations as well as residential?

  Yes. They are widely used in light commercial work when installed per manufacturer instructions and local code. Verify any project-specific fire/smoke and listing requirements.

• How do I size a distribution box and branch takeoffs for proper airflow?

  Base sizing on system CFM, available static pressure, and accepted duct design methods (e.g., Manual D). Keep velocities in target ranges and use balanced takeoffs with smooth airflow paths.

• What safety precautions should I follow when handling fiberglass duct board and wrap?

  Wear PPE, cut in a ventilated area, control dust, and clean with a HEPA vacuum. Avoid skin and eye contact and follow all product safety data guidance.

• Do local codes require specific liner or vapor barrier details when using duct board?

  Many jurisdictions require specific facings, continuous vapor barriers, and UL 181-compliant closures. Seal seams thoroughly and follow any humidity/condensation provisions.

• Are pre-fabricated sizes available or can I build custom dimensions onsite?

  Both. Stock plenums and boxes speed installs, while duct board sheets let you field-fabricate custom sizes to match equipment openings and spacing.

• Can I mix metal duct with duct board and flex duct in one system?

  Yes. Use proper collars, takeoffs, and connectors to transition between materials, support per code, and seal all joints with approved UL 181 closures for an airtight system.