Fiberglas insulation directly against chimney flue?

I'm trying to solve an insulation problem. I've got a zero-cleatance wood fireplace, with the metal flue (10" round?) going through the roof inside of a rectangular 2 foot by 4 foot plywood chase. I discovered that there is no insulation in the chase, and indoor heated air is virtually free to flow up the chase and out the top. (The chase is interior, not on an exterior wall, and the interior sides of the chase were not insulated. With the essentially open chimney top, this seems equivalent to an uninsulated exterior wall on the inside of the house). I'd like to interrupt the air flow somwhow. Code says you can't put wood (or other combustables, I assume) within 2" of the flue. I'd like to pack the chase at the rafter level with fiberglas insulation, which means the fiberglas will be in direct contact with the metal flue. Is this a potential problem? I don't consider fiberglas combustable, but what do I know. If it is a problem, any other solutions come to mind?
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No expert here by any means. IMO best action is to check with your local code enforcement people. In my experience the reqs are different from place to place and unless it was a neighbor responding, they wouldn't be able to give you a very high confidence rating that the answer was accurate for you specifically.
Also, the situation you are in might, depending, be an invitation to create moisture problems either for your wall or for the chimney material itself.
In my case, I installed a double-walled pipe to get thru the wall and then insulated around that. Inspector said it looked fine. Then he wanted to look inside the chimney opening - that scared me, but he said it was OK.

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Check into something called ROXUL. http://199.202.236.133/usa/why_roxul.asp It is insulation made from granite. It is rated for no combustion at higher than 1800F. I found it at a local lumber store. I believe it cost me $8 for a 2ft x 4ft x 3" chunk. I used it to insulate the back of my fireplace insert.
Bob
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Oops. It's really made from basalt.
Bob
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Actually, it's mining slag.
Better to use Roxul than fiberglass for this application, because the binders in fiberglass are flammable and will give off fumes.
It's generally no more expensive than fiberglass insulation [$8 for _one_ batt is okay. But if you're buying it for general insulation, that price is at least triple what it should be.]
But I'd check code first before doing this.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Single or double wall flue???? When it was installed there should have been fire blocking very at a minimum 8 feet. You have fire blocking in your stud walls every 8 feet at a minimum some building codes require every 4 feet. Do not put fiber glass directly in contact with the flue unless it is triple-wall. It really does get that hot. You need to look into some draft protection. There are a bunch of products out there but none are made to cover much more than an couple of inches of space. I suggest that you contact the building department and ask some anonymous questions. like in person...... never over the phone.
The other suggestions were good.
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