I am replacing 20 year old bathroom fans with a new Panasonic fans. I'm starting with the easy fan that vents into the attic crawl space. This fan vents into an aluminum duct that extents about 4 feet towards the roof, missing the attic roof vent by about 18 inches. Also the duct is duct-taped to the attic rafter and not fastened with a hard fastener. I suspect this was done so that the duct could be attached to something. Otherwise, it would extend from the fan exhaust to the roof vent without any support.
Is this acceptable? Should (must) the the exhaust duct extend all the way to the roof vent? If so, how do I fasten it to the vent?
I'll post a pic if I can figure out how. Also, I'm located in mid-Atlantic, near the District of Columbia, so we have moderate winters but brutal hot and humid summers.