Duct tape is useful for repairing just about anything, but ironically, not for ducts.
Although the name might be misleading, general purpose duct tape was not designed for use in HVAC ductwork at all. In fact, if you tried using “regular” duct tape on your ductwork, it would more than likely fail. The adhesive used in general purpose duct tape is not built to withstand the conditions that HVAC-specific tapes are tested to perform in. Cold and hot temperatures can cause this type of duct tape to flag and fall off, leaving leaks in the system that can result in energy loss and expensive heating and cooling bills.
In cases where general purpose duct tape is used to seal or repair a leak in an air duct, the tape does not provide a long-term solution, as it often fails within a few months if not a few days. For a true, permanent solution to air leaks, a higher performing, professional grade HVAC duct or foil tape is the best option. This will ensure full system closure, leading to lower energy costs and a better-functioning system.