Well after seeing some condensation in the chimney, I am going to get a liner. We have a exterior masonary chimney thats a 7x11 or 8x12 flue. We never had any issues with condensation on the old woodfurnace because of the extra heat going up the flue. We haven't seen alot of buildup with the new furnace, and it drafts fine (Verified with Manometer), but the gasses are cool causing condensation. We need a 30' liner, and I think I'm going to use vermiculite as insulation for the liner. What I can't get in my head is if I need a cleanout, or not. The current chimney has one below the thimble. In the past I have removed buckets full of creasote with the old furnace. With the new furnace its been nothing. So with that said, could I just cap the base of the tee and not have a cleanout, or run a section of liner off the bottom of the tee for a cleanout below? I'm afraid of the connection at the thimble clogging, because I am used to the old furnace. Maybe i'm being paranoid.