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

Duct tape is not typically an approved method for sealing duct board. While duct tape may have been popular in the past due to its versatility and ease of use, it is not recommended for long-term sealing applications in HVAC systems. This is primarily due to its propensity to lose its adhesive properties over time, especially when exposed to varying temperatures and moisture levels that are common in air distribution systems.

In contrast, mastic, PVC tape, and foil tape are designed specifically for the purpose of sealing duct boards. Mastic is a thick adhesive that can effectively seal ducts, filling in gaps and providing a durable, long-lasting seal. PVC tape is designed for use in HVAC applications and provides a reliable seal because it can withstand the conditions typical of ductwork. Foil tape, often made of aluminum, is also widely used for sealing duct insulation and connections, as it is resilient and adheres well under various environmental factors.

Understanding the appropriate sealing methods is crucial for ensuring energy efficiency and system performance in HVAC applications, making it clear why duct tape does not meet the necessary standards for sealing duct board.