Which type of duct tape is prohibited as a sealant on metal ducts?

The prohibition of unlisted tape as a sealant on metal ducts is based on safety and performance standards outlined by the North Carolina Mechanical Code. Unlisted tape lacks the necessary certification and verification for reliability in applications involving ductwork, which requires specific performance characteristics to ensure proper sealing and longevity.

Using listed tape, which meets certain industry standards, ensures that the tape can withstand temperatures and environmental conditions typically found in duct systems. Heat tape is specifically designed for heating applications, and pressure tape is also suited for certain uses but must still be appropriate for the specific materials and conditions. Therefore, relying on unlisted tape can lead to failures such as air leaks, loss of energy efficiency, or even fire hazards due to its lack of proven performance criteria. This is why the use of unlisted tape is prohibited in this context.