Smoke Pipe size

[devils11217]

Working on building my cupola and relocating evaporator to new sugarhouse. My evap is only a 2 x 4 with 2 blowers on it... it has a 8 inch dia smoke pipe.. i have a 6 inch dia metalbestos chimney system lying around that i am thinking about using but worry the downsize in diameter may be too severe although it will be fairily straight up and out whats peoples thoughts on this? Whats a cost effective method to do this if i need larger pipe. Pictures would be great. Thanks in advance. P.S. dont want to burn down my shack either.

[maple flats]

6" should be fine. Most older 2x6's came with a 7" or 8" stack, a 6" should handle a 2x4 fine. Make sure it is min. 8', better 10-12' tall. If you need more draft, just add more stack. Above the roof you only need single wall.