Stack size.

[tonka]

I am making my own smock stack, is there a rule of thumb for smoke stack diameter? I made my self 2 21" by 6' long pans that I will be having side by side on one fire (42" by 6' pan) I also plan on either making a flat bottom pan or a raised flue pan next winter that will sit at the smoke stack end of evaporator, that will be either 3' or 4' long by 42" wide. I was planning on making the pipe around that 11". I appreciate any knowledge that you all have!

[bowhunter]

I'm a newbie at maple syrup, but I do have some technical background and industrial experience with furnaces. You need to determine how many square inches of stack is required. To do that you would take the stack size required for each pan and add the cross sectional area of each stack together and then calculate the diameter required. You should be able to get an idea of the stack size required for each pan by looking at some of the manufacturer's catalogs. I'll do some of the math as an example.
4 inch stack = 12.6 square inches of cross sectional area
6 inch stack = 28.3 square inches
8 inch stack = 50.3 square inches
10 inch stack = 78.5 square inches
12 inch stack = 113.1 square inches

So here we go if you had three pans that required a 4 inch stack, a 6 inch stack and a 6 inch stack, you add together the areas for the three stacks.
12.6 + 28.3 +28.3 = 69.2 square inches. Therefore the 10 inch stack is closest to the correct size. I hope this helps also some of the more experienced viewers might be able to critique my calculations.

[tonka]

I don't think anyone could have answered it any better. When I made my stack pipe I figure better too big then too small, I used a couple five gallon buckets to wrap the stainless steel around to get it round so I have about an eleven inch pipe. Thanks for your input and explaining how you figured it all out.