What is the appropriate description for the material used for duct construction that does not need sealant?

The appropriate description for the material used for duct construction that does not need sealant is welded duct. Welded ducts are typically constructed from metal that is joined using welding techniques, which creates a continuous and airtight seam. This quality eliminates the need for additional sealants, as the welds provide a secure and leak-free joint, making them ideal for high-pressure applications or situations where maintaining a specific airflow is critical.

In contrast, flexible ducts are often made from materials that may require sealing at the joints due to their construction, which is typically not designed to be fully airtight without additional measures. Insulated ducts, while they can maintain temperature, still often need sealant to ensure they do not leak air or allow condensation. Riveted ducts can create strong connections but generally require sealant to prevent leaks, especially when used in HVAC systems where air pressure and efficiency are crucial.

Thus, welded construction stands out as the method ensuring an airtight construction without the need for further sealing methods. This quality makes welded ducts a preferred choice in certain HVAC applications.