What is the difference between Duravents "Pellet Vent" and "Pellet Vent Pro" series pipes? I mean the catalog descriptions look the same. The parts have different part numbers, though. I believe the components will interchange between the different styles. Does the Pellet Vent Pro style omit the rope gasket within the sections? I think the pro series costs more, what justifies the price? I ask this because if I ever buy new pipe (new install or replacement parts) would I look toward updating to the pro series? I must have the basic Pellet Vent style because it is over 5 years old.