gap between chimney and wall

This past weekend I was up in the attic getting ready to lay down some insulation when I noticed that there was a pretty big gap between the chimney and the adjoining wall running pretty much the whole lenght of the chimney. I wasn't able to get close enough to measure it, but I'd say it's close to an inch pretty much the whole way.
Is this something I can seal with a can of the spray foam sealant or do I need something else?
TIA, tmo
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That's supposed to be there. It keeps the chimney away things that burn, so that your chimney fire doesn't cook off the rest of the house. I don't think you should seal it at all, but if you do, use something that's both non-flamable, and which doesn't conduct heat well.
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You can't seal it with anything flammable. If you want to stop the cold air from flowing down along the space, you can use metal flashing.
HTH,
Paul
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