Math and FB to CB deminsions

Discussion in 'Reverse Flow' started by svaillan, Mar 21, 2014.

  1. svaillan

    svaillan Newbie

    Hello all. Here is what I have so far for math.

    124gal Tank
    24 1/4" wide
    12 1/8" Radius (or 12.125)

    Cooker Chamber Size 28644.00
    Recommended Firebox Size 9548.00
    Recommended Chimney Volume 494.00
    Recommended Air Inlet Area 29.64
    Recommended Firebox-to-Cooker Opening Area 79.04

    I tried using this excel sheet for figuring out the FB to CC opening. Or the moon cut. of Firebox opening - curved_Simple-1.xlsx

    But I don't get why the 3 sections to it. What I am trying to accomplish is to have the fire box notch on the end of the 124gal tank lower then the center axis and still allow the proper size opening (1/4 moon cut). That way my heat plate across the bottom of the tank has some room between it and the cooking ranks which I would like to be at center axis.

    Once I know how wide that moon cut is I'll know how deep to go with my firebox. From there height and width should be easy. Also I posted the question earlier of does the area in the firebox below the fire crate count toward total volume. I believe it does but I want to make sure. Thanks Steve
  2. pettybilt

    pettybilt Newbie

    I laid mine out on some graph paper like this. Mine required 54 sq in.. By coming up 5 inch I had a little over 60 sq in.. I went 6 to allow room for a baffle plate.

  3. smokejumper

    smokejumper Smoking Fanatic

    I created that spreadsheet.

    All three sections do the same thing: use two of the three dimensions to calculate the third dimension and the resulting area

    Since you know the radius, you would use the top or bottom section.

    If you use the top section, just plug in your radius and then try different widths of the cut (dimension X) until you get the area you want, and it will tell you the height of the cutout (dimension H).
    Last edited: Mar 22, 2014
  4. SmokeJumper,

    Your spread sheet is much easier to understand than others that I have seen links to on this site.  I know that it has already helped a lot of folks and will continue to be an aid to many.  Thanks, Weedeater
  5. smokejumper

    smokejumper Smoking Fanatic

    No problem Weedeater. The math is hard, and it always bugged men when some builders always recommend a half circle (that does not follow the contour of the tank) just because it is easier to calculate. I wanted to make it easier for people to build what they want and not settle for someone else's compromise.

    I may make a simpler version by getting rid of the top two options, since most people already know their radius and just want to try out different heights.

    Perhaps we could start a sticky here for those sorts of tools.


    It only took me about 30 seconds to make it.
    Last edited: Mar 23, 2014
  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    svaillain, morinng...... I would use 115 sq. in. for the FB/CC opening..... The numbers you have are based on Feldon's calculator and have inherent problems.... Those numbers cause an overheated FB....
    For the semi-circle opening between the FB/CC, use ...

    For your smoker build, 12" radius of the ID of the CC.... a 7.25" segment height ED.... Chord AB would be the width of the RF plate at 22".... click the Radius and Segment Height ED variables.....

  7. SmokeJumper,

    Taking the top two options out was a good idea and should serve everyone using a round tank very well.  Only draw back may be for some folks who don't have excel.  Apple users in particular may have an issue.  What is the Apple version of Excel.  Think a sticky would be a great idea.
  8. Sorry duplicate post.
    Last edited: Mar 23, 2014

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