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We converted a wood stove to a propane fireplace. It's a direct vent but we're only using the exhaust insert. The intake air will come from the interior.

Anyways, as such, we have a gap around the new flue insert and the flue. What kind of insulation can I use to plug up that gap at the bottom to prevent cold air from pouring down in the winter?

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up vote 2 down vote accepted

Mineral or rock wool is what it is called, I believe Roxul is a brand of that. Check its properties to make sure it can handle that kind of heat. It is approved for firestopping in framing of homes.

Here is a video of it's benefits

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Thanks! Went to the fireplace shop over the weekend and they had something just like this (a ceramic wool). – DA01 Jun 16 '14 at 22:06

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