yardatwork, although you think the wood is dry, you need to be really sure. Split a few splits in half and check the fresh surface of the wood for moisture. If you don't have moisture meter, put it up against your cheek and see if it feels cool and damp. The chimney is too short. With the resistance of 2 90 deg turns it is effectively about half the 12ft height or 6 ft.. As a test, get a 4' length of inexpensive 6" galvanized duct pipe (at Lowes or HD),and use that as your test extension. Try a burn with known dry wood, not too large splits (say 3-6") in the stove and see if you note a real difference.