Hello:

Just found a crack/tear in the 3" diameter round sheet metal duct that
funnels the exhaust from a gas fired water heater (the typical cylindrical
type) to the main duct going to the chimney.
Probably about 1 to 2 inches in length.

Looks like it is a big job to replace the duct.

Was wondering -

Is it code permissible to place a conforming metal patch, perhaps held on
with two pop-rivets,
over the cdrack ?

That sure seems to me like a simple approach, but before I get a contractor
in I wanted to ask here. If a good idea, and code allowable, should some
kind of "gunk" be placed under the metal patch also ?

How about that metal duct tape ? It certainly would seal it, but could
this be considered a "permanent" fix ?

Any other suggestions would be most appreciated.

Thanks,
B.