Hello - I'm getting new siding on my house in the fall, and I'm looking to replace my Wall Thimble and vent pipe. Straight out from the back of the stove, "T" with clean-out on the outside, and up 3'. My questions: 1. What brand thimble has a 2" OAK built in? 2. For the straight out section, should it pitch slightly upward from the stove, slightly downward, or level? Thanks.