Arch build stack question

[Someclown]

Just wondering if this opening is going to be big enough for a 2x3 arch convertable to a 2x4 if needed in the future. I am going to use a 6 inch chimney and the hole I cut out for the stack to chimney is 2 x18 inches.
The square opening in the picture is what I'm questioning.21440
I will be using a flat pan and wood fired
Thanks for any feedback

[Bucket Head]

The width of it is good. You want the heat to flow evenly underneath your entire pan and then up and out. A narrow opening forces the heat to "funnel" inwards towards the smaller opening, causing the rear corners of the pan to be cooler- with a noticeable lack of boiling.

You will have to do the math. Is the square surface area of that opening the same (or pretty close to it) as the 6" round pipe?

I'd say by looking at it that it's a good start. Better than the simple 6" hole my first arch had originally...,lol.

Steve

[Someclown]

Thanks BH
The area of a 6" circle is 28.27sq" and the area of this opening I have is 36sq". Would it be an advantage or disadvantage to make it 52sq" for an 8 inch pipe also for future upgrades
I figured that would be plenty but wanted to be sure I dont have to calculate some crazy thing like volumes. I'm hoping the opening will create enough draft for non fan and future fan
I dont want to go big right now because I dont have the resources and I will not be doing umm much more than 50 taps for a while, lol that's what we all say! right

[maple flats]

I think you'd be better off making it 4x18 now. The 6" stack (or later an 8" ) stack is up a few feet, typically minimum 3 up to 6' above the base opening. The transition then allows the exhaust flow to concentrate to the pipe diameter. As small as a 2x18 gives you the sq. in. needed but it still chokes off the flow. In fact I had my base opening on my 3x8' rig made 32" wide, you will get better results if you widen it to 20 or even better 21" wide. That will help you get the best heat distribution near the back of the pan.

[Bucket Head]

I agree on upsizing. You'll be very happy down the road when you add a few taps and realize you don't have to modify your arch. I have a few "redo's" under my belt so I can speak from experience, lol.

[Someclown]

Thanks for the suggestion maple flats and bucket head.
I am going to make that opening bigger as suggested, I know from past experience with a lot of things, and I always say "better to do it right than do it again"
Back to the grinder. Lol
Thanks again