I am going to install a 27' exterior exposed class A chimney. I look forward to burning bagged anthrcite coal, in a vermont castings vigilant II stove. the stove comes standard with a 6" collar, with an 8" being an option. the price of the chimney pipe is obviously cheaper for 6" but which one will provide the proper draft as I will spend more to get the 8" if that would give me a more appropriate draft. also if there are any obvious problems with the vigilant II stove that I should know. (although any time someone asks "what is the best stove" everyone praises the one they have and dismisses all others; which is in the end ok because that means the majority of people are satisfied with their purchases; boy what a ramble).