What is your ducting made of? If sheet metal, I would imagine that
there are tapes at the box stores that would be satisfactory. The main
thing is that the surface MUST be perfectly clean and dry for it to
stick properly. The duct sealing mastics I use dry within a couple of
hours, but then I'm in S.Tx, so it may take longer at your lower temps,
and of course it will also depend on how thick it is put on. Larry