We have a “pretty good house” that is sealed to 0.8ACH50.  We are having a horizontally vented pellet stove installed with an air intake kit.  My questions is, how should we require the through-the-wall exhaust and intake penetrations to be sealed based on our wall design?  see attached image

I’m guessing that to seal it properly and keep our house “tight”, it should be sealed at our air barriers, which are at the drywall and at the exterior of the 7/16″ OSB sheathing, correct?

The horizontally vented pellet stoves wall thimbles that I have seen are just one ring, or two concentric rings, with the double wall stove pipe going through the middle of it and no insulation in the air gap around the thimble.  Does anyone make anything that is insulated?  I’m sure there is high temperature insulation that would work in this location, but I don’t want to do anything that isn’t safe.

Any input would be appreciated.