Determining stack size

[11-Nick]

How do I determine the proper stack size for a new evaporator? I'm assuming it is a function of the volume of air that can flow under the pan, and maybe whether or not forced air will be used in the fire box???
I did a search. Maybe I missed it, but I didn't see a good explanation.
Thanks

[Loch Muller]

If you are building it yourself, I'd look around at some of the commercially manufactured arches to see what size they use. My old 1/2 pint and 2x4 Mason had 6 inch stack, they worked good especially with AOF. The GH Grimm 30x8 I'm using this year has a 10 inch stack, which seems pretty standard.

[bowhunter]

Precise stack sizing is pretty complicated, but I would just follow the advice Loch Muller gave you. You can't go wrong with that approach.

[psparr]

The ideal situation in your case with a 2' evaporator is an 8" stack. The area of an 8" pipe is 52 inches. If you have 2" under your pan that would be 48 sq. Inches. Which closely matches area of the stack. Whereas a 6" stack is only 28". You don't want to restrict your draft with a small diameter pipe. Forced draft would help to overcome that restriction but it would still be better to go 8".
Also the other rule of thumb is to make the stack twice the height of the length of the evaporator.

[billyinvt]

I am working out a similar problem. I am building an arch for a 2 x 5 combo pan from an oil tank and plan to run the stack out the back with an elbow. The barrel stove door kit comes with a collar for a 6" pipe and I have some more laying around so I'd like to use it. Would there be any benefit to getting an adapter to expand the stack to 8" right before the elbow?

[NhShaun]

I am working out a similar problem. I am building an arch for a 2 x 5 combo pan from an oil tank and plan to run the stack out the back with an elbow. The barrel stove door kit comes with a collar for a 6" pipe and I have some more laying around so I'd like to use it. Would there be any benefit to getting an adapter to expand the stack to 8" right before the elbow? I was wondering this as well. It might help a little bit, but the main exit of the stack will still be limiting air flow with the 6". I have come to the conclusion to use 8" pipe on my 2x6 block arch.

[maple flats]

From the piece you cut out to open the top, weld it to the back of the arch to create a base stack . Then weld an 8" heavy gauge steel collar on the top of that. From there you can use galv. smoke pipe, at least 24 ga or heavier. An elbow will restrict flow enough to cause an issue. A short piece of 8" black pipe, fitted to the round top on the part you welded at the rear for a base will make a good starter.