Screw it. After 6+ years of wondering if I should switch to double wall pipe, I'm going to try it. I had a 1/3 full load of wood practically overfire last week with the air completely shut. I'm sick of watching my single wall pipe at 400 while my stove is only at 250. Obviously there is way too much heat leaving the house than heating the room. I'm told this is common with the Hearthstone Heritage. Anyway, I'm going to include a damper with the new pipe. How far up the line do I put it? My set up is approx 24" from stove to elbow, then right angle to thimble in wall. I would look in the manual, but I'm at work and figure you guys know anyway. Also, I'm seeing a lot of the corrugated looking double wall pipe. Besides being ungodly ugly, does it serve any purpose over the old style smooth stuff?