I recently bought 2 us stove company king 5502m pellet stoves. One is for our old house that we rent out. I'm taking out a hearthstone wood stove and putting in one of the pellet stoves. Can I use the 3" pipe? It will be coming out of the stove and up about 6' into an existing 8" metalbestest pipe. The other stove will be in our basement and coming out of the stove up 5' 90 elbow into an existing 6" stainless chimney. The 8" chimney is 18' tall and the 6" is about the same. This is our first time with pellet stoves so trying to install right to not have problems thanks for the help