Perlite, vermiculite or mineral wool?

[Black Jaque Janaviac]

I've got an old stone chase with three terra cotta flues. One flue is occupied by the living room fireplace insert liner. The second flue will soon be occupied by another liner for an NC-30 which will go in the basement. And the third flue is lined with what appears to be galvanized gas vent liner.

I've gone up to there in the winter while the living room insert was burning and noticed that the heat radiates from that flue into the others. This warming of the two unused flues I'm sure causes them to draft. I covered them from inside the house with plastic wrap and you can tell they are drafting by the way the wrap is sucked in.

Anyway, after I get the NC-30 installed I want to fill in the gap between liner and terra cotta to help eliminate extra draft. Doing a little research it looks like the best materials would be either Perlite, Vermiculite, or Mineral Wool. The Perlite and Vermiculite might be the easiest to dump down.

What would be the most economical?

And where would be the best place to find these materials at reasonable costs? Home Depot and Menards has them. My local landscaping place does not.

 

[branchburner]

Perlite is cheap at a good masonry supply store. Be aware that using it will probably not conform to the approved insulation methods listed by the liner manufacturer, meaning your install may not technically be to code (but that didn't stop me).

I plugged my unused flue at the top, as well as the bottom, to reduce draft. I assume you have (will have) a top plate sealing the lined flues.

 

[Prosecond]

I used an insulation wrap on my liner and then filled thfe space with vermiculite.