How should I fasten air exchanger ducts to unit?
I agree with Michael, and add that you could also use large HVAC zip ties. If the lines seem to come loose easily, then you would be better off using a tape. Now, "Duct" tape and "Duck" tape are not the same. "Duck" tape is what most people see as the old fashion silver/gray colored roll of tape that now comes in wild designs and colors and can be bought at every store that sells tape. "Duct" tape is designed for duct lines, HVAC, and is usually an aluminum foil type tape, and a common brand is 3M.