Finally Going to Start

Discussion in 'Reverse Flow' started by smokingdreams, Sep 25, 2013.

  1. Cant Seem to find the calculator to do some figuring, So if anyone can post a link to the calculator that would be helpful. The old tank I picked up is 52" on the weld centers, and has an O.D of 24".(feel free to help with calculations especially being a reverse flow) Don't plan on putting this thing on a trailer more of a post mount swivel, swivel will be a simple pipe, inside pipe, so that I can turn the firebox into the wind if needed, Single Door, hopefully I have room to mount a top rack. Also if anyone remembers a post with a smoker with hatchets as handles that could post a link would be nice as well.

    Last edited: Sep 25, 2013
  2. radioguy

    radioguy Smoking Fanatic


    Find a post by Dave Omak.....calculator link is in his Sig line. You can Google feldons pit calculator also. Do your homework'll save you time.

  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Here you go......
  4. Quick question using this calculator, Do I need to take into consideration of the space of the tanks end caps as cooking area, rather than just weld centers.
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Measure the length of the domed end, add about 60-70% of the straight walled volume and double it to take into account of the other end....  It's not that critical for an exact measurement...   
  6. Thanks for the reply didn't think it would matter to much, but I addend 2" each cap runs 24" Dia. for about an inch before it makes its radius.

    Using the Calculator This is what I came up with.

    Using 54" and 23.5 I.D

    CC = 23409.88

    Recommended Firebox 7803.29 Cu in.

    Actual Firebox 20"H X 20"W X 22" L = 8800.00 Cu In  112%

    Stack 4" x 35"L

    Air inlet to firebox, 3" x 3" Sq. = 3 needed, Most likely will do 3 on each side of the Box

    Firebox to CC area Recommended. is 13.39 Recommended Dia. with 70.40 Sq in.

    Playing with the Circle Calculator I came up with a radius of 13.5 with a segment height of 5" = 73.003 Segment area

    (hopefully this is right the segment area)

    Will post some pictures soon. Going to shear some 1/4" tomorrow or Friday.

    Thanks for all your help with this build.
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Those numbers seem a little off.....  Dave
  8. Dave,

    All the calculations or just the firebox to cc cutout?
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    SD, morning.....  I wouldn't use Feldon's for all the numbers...  there are some inherent problems with it...  Use the circle calculator for the FB/CC opening....  That will give you more room for cooking in the CC....  If you are building a reverse flow smoker, take the FB/CC opening X 1.5...  When figuring all the smoker parts, use the recommended FB size for all the calculations, keep those numbers, then make adjustments to parts.... ...
  10. Maybe I am not thinking this just right, Feldon's calculator came up with 70 cu in,  So 70 x 1.5 = 105 cu in

    Using a radius of 12", and a Segment height of 7 in Came up with this on the circle calc

    Chord AB 21.817 with a segment area of 109.76

    If this is the way I should go, Then I must change my firebox design to match the width of the segment.
  11. Those still seem off to me given the chord is almost 22" that would put the RF plate pretty much dead cent inside the tank
  12. Dave thanks for all your help, Your input is greatly appreciated, I promise I won't have anymore questions once I have these numbers figured out, The actual welding/fabrication part is my specialty,
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    SD, afternoon......

    FB/CC opening...... 62.4 sq. in.   x 1.5  =  approx 92 sq. in.    

    radius              = 11.75"

    Segment Area = 87.35

    seg. ht.            = 6"

    chord AB         = 20.49"

    Opening at the end of the RF plate 7" plus for extra room and reduced friction...

    I think where we screwed up is......   I use the size of the CC as the primary for doing all the other calculations.....  The CC has no idea if the FB is made larger... Same with the exhaust stack and FB air inlets......   

    Sooooooo... I enter the CC size and note the recommended sizes for the other variables....   Calculate the FB/CC opening, Exhaust stack, FB air inlets all from the recommended numbers for the size CC entered into the calculation...  That includes the recommended FB size.... 

    Since the CC works well with the recommended sizes, making them larger won't affect the cooking ability.....  Raising the RF plate and enlarging the FB/CC opening won't affect the cooking ability of the CC...  It will affect how the smoker breathes and reduces the over temp problems with the FB thus reducing fuel consumption, especially if an additional air inlet is installed directly across from the FB/CC opening...

    taken from Feldon's calc....   I used the recommended FB size from the original calc. using the CC volume to plug in the equation below...

    Recommended Firebox-to-Cooker
    Opening Area

    (firebox volume * .008)

    square in.

    Below is how I determine what sizes are appropriate for a smoker.....    Then change the FB size if you want, change anything you want...   but the CC can't be changed and the numbers below are what's necessary for the CC to work....   I changed the RF plate number some time back, and added an additional "above the fire grate" air inlet to help cool the FB and improve fuel consumption......

    Link to BBQ Pit Calculator

    You think reading my ideas, put in print, is confusing....  Try pulling it out of my head and putting it onto paper.... That's the tough part....  

    Let me know how bad I confused you and I will do my best to straighten out what I screwed up.....   

  14. Dave,

    Thanks for explaining those things to me, I failed to realize in the calculator that changing the firebox dimensions, also changed the recommended cc/fb sq in. Have enough info to shear some plate now, glad I didn't go and do it today. Will get started cutting this weekend and will start posting some pics of the build
    Last edited: Sep 26, 2013
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Does it make sense the size of the FB shouldn't change all the other dimensions.......    Dave
  16. Dave yes I do understand what you are saying, CC remains the same. Changing part dimensions should will not affect CC.
  17. Well I finally got to do some things to the smoker this weekend Here are some pics

    Tank I picked up from a friend for free, Has a good amount of pitting but for free I can't complain

  18. Cutout for the Firebox

    Door Layout, Ready to cut

    Door Cutout ready for some hinges and welding, Will use 1/4;" X 2" with some gasket for a nice seal

  19. Cut Stack, Still have to cut to length, but I am going for a two tone look so used stainless

    Stack Damper,

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