As we mentioned before, duct tape should NOT be used to seal your home's HVAC ducts. Putty or aluminum tape is a better choice for that job. Another thing to clarify here is the difference between “adhesive tape” and “adhesive tape”. Duck Tape is a specific brand of adhesive tape, as are Gorilla Tape, 3M and many others. How do you know that your ducts are leaking in the first place? The first step for homeowners is to inspect duct joints to see if any of the above tactics have been used.
The best person to locate leaks is a qualified professional who checks the fan door and observes the pressure readings on a pressure gauge. Accessible ducts can be sealed with putty or adhesive tape with an aluminum backing, while the injected aerosol sealant serves to seal inaccessible ducts located behind finished walls. The adhesive tape can adhere to even the toughest surfaces and is able to withstand a lot of things. But it does not withstand extreme temperature changes in air ducts well.
Heating cycles can cause the adhesives on the adhesive tape to break. Over time, the adhesive tape weakens and ends up falling right away. In 1998, researchers at the Lawrence Berkeley National Laboratory (LBNL) conducted a 3-month experiment to see if adhesive tape, along with 31 other sealants, could withstand typical conditions which are found in air ducts. But back then, just like people now, the military discovered that duct tape had a variety of other uses, such as quick repairs.
The advantages of an adhesive tape specific to air conditioning systems for applications such as sewing and sealing class 1 flexible ducts include that it adheres to rough or dirty surfaces, is easy to tear and offers high retention capacity. While general-purpose adhesive tape is not suitable for use in HVAC systems, there are some fabric adhesive tapes that are specifically designed to be used in certain HVAC applications.