I'm installing 3" double wall pipe through my basement sheetrock wall and out through the concrete foundation. I'm planning on using a Duravent 3" wall thimble and running a couple foot sections of vent pipe through the thimble to get at least 12" away from the outside of the house. My question is this - In the pellet stove manual I'm looking at it, a diagram states a "heat resistant material" is inbetween the two sections of the thimble and around the pipe inside the wall area. Is there a special type of insulation that should go around the 8 inches or so of vent that is located in the walls or should I just ensure the immediate area is clear of anything? To give a better understanding of my setup I will be installing a pellet stove in my basement connected to a stove adapter/coupler - Tee Vent - 5' vertical pipe - 90 degree - 2' horizontal through thimble and outside - horizontal cap. I've attached the picture of the diagram for reference. Granted my installation isn't straight horizontal, but I just wanted to make sure. Thanks!