I recently installed a Quadrafire Castille Insert. I framed around the unit. I am using the new Duravent Pellet Pro pipe (Double walled, 3 " pipe, 1" to combustibles. I have a vertical rise of 5 1/2 feet into a 90 then a 1 foot section into a 45, then 6 feet horizontally to the outside, equivalent pipe distance of 18 1/4 feet). The pellet insert seems to be operating properly as per the instructions in the manual. I understand the quick smoky fire at ignition. This new pipe is supposed to be airtight and no silicone required at the joints. However, I am getting smoke coming out of the cavity between the inner liner and the outer at the stove outlet to vent pipe. I have put two rows of 3/8 beads of silicone where the pipe connects to the stove and have sealed most of the joints in the pipe run. Specially, the elbows and horizontal joints. Again, the smoke comes from the 1/4" cavity and the outside liner,at the stove location. But, it's not the joint to the stove itself. . Any ideas?