I’ve seen this goo a few times on vent connectors. My guess it’s regular duct tape that the adhesive has melted. Would you agree? I’ll probably write something like “improper tape used…”. What do you say?
Thanks
Yes, it looks like adhesive from some type of tape, also by looking at the solder joints it looks like a non-professional installation. We will have to ask @mwilles about the tape, but I have never heard of taping vent pipes.
Scott that tape residue is a mystery to me. The things people come up with instead of installing appliances correctly 
1 Like
I googled tape on vent pipes and it said it is a fire hazard?
I’m sure it is Scott. Flue pipe guts cut, crimped and screwed together with no less than 3 screws.
2 Likes
Thank you Scott and Martin!
2 Likes
I am seeing a fiberglass patch job on that vent. The goo is excess resin.
4 Likes
It does look like that! Thanks Duane.
That’s what I thought I saw. Either way (Fiberglass or duct tape) it is wrong. Fix it.