Sealing a Crack In A Metal Exhaust Duct From A Gas Fired Hot Water Heater ?

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.
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Replace it, thats not a big job.
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Is the Flue double walled. A crack in the outer wall but not the inner may not expose you to fumes.
I wouldn't consider metal tape to be perminant but might use it until the contractor can get to you. Though they may stand up to HVAC ducts, an exhaust flue can get very hot and I don't know of any tape adhesive that will last long like that.

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Just to explain further, a double walled duct combines intake and exhaust in one pipe. If the inner wall cracks, the idea is that the flame will go out as a safety measure. If it is a single wall duct then unless you enjoy carbon monoxide poisoning, replace it.

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What about JB Weld? I don't know if it would work. I don't know if it would be safe. I don't know much ;>0
But, you might investigate and see what you think
.. http://jbweld.net/faq.php#faq001
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wrote:

Assuming you are talking about a 3" dia piece of stovepipe, just replace it. Why are you making a mountain out of a mole hill? Duct tape may start a fire too. Just replace it and be done with it, The stuff costs less than $5 for a section.
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