Air tight sealing poly vapour barrier to Selkirk Supervent 2100 Chimney

Greetings,

I'm about to purchase and install a Selkirk Supervent 2100 chimney in our new home. Going with Supervent 'cause it is affordable and available at the local Canadian Tire. We are aiming to built a very air-tight home, so we are sealing the poly air/vapour barrier as tight as we can at every hole. Our home is 2 stories with the stove on the first floor, so the chimney goes through the ceiling, into a chase through the second level and then through an attic, which is where I need to seal it to the poly.

The Selkirk Installation manual warns several times that the gap around the chimney should NOT be sealed to the attic insulation shield. It suggests that we install "Universal Shielding Insulation" (JUSI) to "stop cold air infiltration", but this is just a piece of fibreglass batt insulation - certainly not an air tight seal.

Just curious if anyone has experience with this - Isn't it fairly common to seal the gap between the chimney and the attic insulation shield with high temp silicon sealant?

I also noticed that EXCEL has an "insulated firestop" that they say allows a fully air-tight seal - anything similar available for the Supervent 2100?

Update - just talked to Selkirk rep. They say that no chimney can be sealed air-tight because the testing codes require a 1/8" gap for thermal expansion.

They also mentioned that high temperature silicon would not hold up through a chimney fire because the chimney surface could reach 1000 deg F.

Comments?