140 gallon first build question on cc/fb opening

[ac600]

Good morning,

After months of reading here, Ive decided to finally step up my game and build my own rf. I have a tank, and just have a few questions before i start cutting it up.

My tank is 30" diameter, and 46" length.

Running the numbers, I came up with

140.76 gallons
32,515.56 cu in
130 cc/fb opening
10,730 firebox volume

I have an old wood stove that has inside dimensions of 24"w x27"d x 18"h

• First question is would this make an ok firebox? It is quarter inch steel.
  
• When i run the calculator to get the fb cutout, do I use the radius of the cc? Doing this gives me a AB chord bigger then the width of my planned wood stove firebox. Do I need to just build one? Or am I messing something up with the calculation.
• What exactly is meant by "Area under the rf plate"? I understand all the other measurements needed, but not sure exactly what this one is.

Thanks in advance for your help, have seen many nice looking rigs come out of this forum, and would like to make sure mine does as well.

 

[daveomak]

Your numbers are correct....
The area under the RF plate is the same as the FB/CC opening... it is calculated to "eliminate" friction loss in the air flow so your smoker works well...
Exhaust stack volume...
32,515 X .022 = 715 cu. in .
You want a stack ~35" above the CC to facilitate good air flow...
32,515 / 0.7854 = 911 / 35" = 26 sq. root = 5.1" stack internal diameter... 35" tall above the CC ...

FB/CC opening 130 sq. in .
using the circle calculator... 7.5" ED (Segment Height) returns a segment area (green area) of 138 sq. in. which is perfect...

The area at the end of the RF plate needs to be at least 130 sq. in. + because the air flow takes a 180 turn and there's a lot of friction when that happens... causing a problem with air flow...

Yes, your wood stove doesn't fit the chord AB dimension.. (26") which is also the width of the RF plate...
It's best to build a new FB that is ~27" wide so it fits up to the end of the CC... If you cut out the end of the CC to slide the FB into the CC as far as you like, then the RF plate can be welded up directly to the top of the FB..

 

[ac600]

Thanks for your prompt reply. I apologize if i am being dense here, but just want to clarify. Are you saying this is the same number as the opening, and nothing more then that? Not the area of the rf plate?

 

[daveomak]

What exactly is meant by "Area under the rf plate"? I understand all the other measurements needed, but not sure exactly what this one is

Yes.... under the RF plate... FB/CC opening.... at the end of the RF plate....
It is the "channel" that allows air/heat/smoke to travel to get to the food....


....

 

[ac600]

ok, thanks again. I figured i was overthinking it.