I just purchased a used St croix afton bay and it came with 3 feet of 6 inch chimney pipe that has the cold air built in. However it screws together instead of locks like the duravent pro. I need to purchase more piping does anyone know where I can get more or should I start from scratch? Also I'm using a masonry chimney that was used for a wood stove. Is there anything special I need besides the thimble adapter? I'm pretty new to this stuff so any input is appreciated