I've been asked to install a pellet stove to replace a wood stove. The existing vent looks like Simpson Duraplus 8" inner and 10" outer. I asked my stove suppliler if they can sell me a transition connector for 3" pellet vent to the 8" Duraplus. He said he could but that his installer recommends sleeving through with all pellet vent but wasn't totally convincing me on why (something about fly ash accumulation). The existing vent is through a chase in the center of the house and runs straight up through two stories to the roof cap. I would think that if the vent is cleaned well it would work to simply connect the pellet stove to it. Anybody know about this or think of a reason not to do it?