I would add hex drive, sharp tipped sheet metal screws - three per
joint. Gray cloth duck tape (original name) was never meant for
HVAC install. You need real metal duct tape. Example:
http://www.pplmotorhomes.com/parts/caulks-sealants/388521.htm

After screwing and taping you can also apply duct sealant. Here
is one we use:
http://www.fosterproducts.com/Images/childers_tds/cp-10-11.pdf
It is quite easy to apply with a throw away paint brush. If the
holes or gaps are huge, add fiberglass reinforcing mesh.


(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"peter" wrote in message
news:CDy%e.2738$kl3.322@trnddc08...
Some of the air duct from the furnace to the registers are
several shorter ducts joint together. A while ago I found some
of those joints failed and separated in the crawlspace. The
ducts look to be 8 to 12 inches in diameter, and they want to
pull away from each other at the joints, perhaps the ducts were
taut when installed. I duct taped them back. Although they hold,
they seem to be leaking air.

What is the best way to seal the joints?