Which of the following is not approved for sealing duct board?

Duct board requires a specific type of sealing material to ensure proper insulation and air quality. Duct tape, while commonly used in various applications, is not an appropriate choice for sealing duct board joints. This is primarily due to its tendency to degrade over time, especially in environments that may experience temperature fluctuations or moisture. The adhesive on duct tape can lose its effectiveness, leading to potential leaks in the ductwork, which can compromise the efficiency of the HVAC system.

On the other hand, foil tape, mastic sealant, and weatherstripping tape are designed for better durability and performance in HVAC applications. Foil tape provides a strong bond and can resist high temperatures, making it suitable for sealing metal ducts. Mastic sealant is a viscous material that adheres well to various surfaces and remains flexible, which helps maintain an effective seal over time. Weatherstripping tape is typically used to seal gaps and can be applied effectively to improve the air-tightness of ducts.

Thus, the designation of duct tape as not approved for sealing duct board highlights the importance of selecting appropriate sealing materials to maintain the integrity and efficiency of HVAC systems.