Insulating Clay Flue Liner

[ultrasport]

Just finishing up on my Clay flue liner and I left about a 3/4" space between the brickwork and liner. What's best to insulate the area with a Vermiculite/portland mixture or just use some of my left over ceramic blanket?

[david s]

You could use either but stuffing blanket into a 3/4” space is difficult and the blanket tends to compress which reduces insulating capacity. It is easier to pour in loose perlite or vermiculite no need to mix cement and water with it, but top the space with about an inch of 5:1 vermicrete to prevent water or animal entry at the top. This technique also works well to fill the space between a double stainless flue pipe system.