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Discussion in 'Reverse Flow' started by newsite smokers, Nov 1, 2013.

  1. Ok here is the problem Somehow I got my figures mixed up and made my firebox to big! According to Feldon's pit calculator now I cant get the FB to CC opening big enough. It recommends 110.59"sq and for me to have 5" between cook surface and RF plate I can only get around 76" sq. Even if I move RF plate up to only 3" below cook surface I still only bump opening up to about 100" sq. But would you want RF plate that close?

    Here are my numbers.. any help would be greatly appreciated. 

    All I have done so far is cut door in tank ( bottom of door is at widest point of tank) and built firebox (all but door piece is welded in place with grate and ash box in bottom)

    It being a RF is not set in stone 

    80 gal tank 24"X46"

    Firebox - 24"X24"X24" 
  2. Hello NewSite Smokers.  [​IMG]   I am not understanding your problem.  Please excuse me for being dense.  The fire box is too big yet you can not get a big enough opening into the smoke chamber and enough space between rf plate and cook surface?  So if the fire box were smaller you could get the opening bigger?  Can you not drop the fire box down; or raise it up?  I am struggling to see where your restriction lies.  I think 3" might just be a little too tight to achieve the full  benefit of a RF smoker.  Just my opinion.   A little more info please.

    Last edited: Nov 1, 2013
  3. lendecatural

    lendecatural Smoking Fanatic

    Greetings New Site,

    I don't think you don't have a problem, it's the way the calculator is set up, it doesn't give you a CC to FB opening until you put in the firebox size but it is tied back to the CC volume to give you the % required to support the CC. It's OK to have a firebox that is too big, you are really worried about how air flows through the cook chamber. Therefore, if you adjust some artificial FB numbers (ex. 20x24x15) you put into the calculator to assure you have more than 100% of the recommended size for your CC you get about 60 sq-in for 116% to support your CC. Does this make sense?

    You will be fine and in the long term, I'm sure you will appreciate the extra room, you could even add fire brick inside like one of the other builders did with room to spare.

    I'm sure someone will come along and correct me if I'm wrong, but it appears that is how the calculator is set up.

    Last edited: Nov 2, 2013
  5. foamheart

    foamheart Epic Pitmaster OTBS Member SMF Premier Member

    You need to talk to DaveOmak, he's the master wizard at construction and calculations. Drop him a /PM
  6. alaska

    alaska Meat Mopper

    Hello NewSitee.... I am also working on my first and let me tell you , If it wasn't for the folks on this forum especially DaveI would have build the coolest looking boat anchor a guy could have. PM Dave and I'm sure he will get you node up. Oh...its nice to meet you and please post photos....
    steve4christ likes this.
  7. Hello.  The guys are correct.  Dave knows his stuff.  It did FINALLY click for me what your problem is.  I agree with Len it is the calculator thing IMHO.  Make your opening the same size as it should be if the fire box was the correct size.  The calculator is designed so that you build the fire box large enough to supply a CC of X size with the correct heat and air flow.  Being yours is larger than needed, should be no problem.  Also.  PM DaveOmak and ask him to take a look.  As stated, he knows his stuff.

  8. Yeah maybe I didn't word my question right.I'm worried about air flow and draw . What us the min space you would put between RF plate and cook surface?
  9. According to the calculator smaller FB required smaller opening.tank it's limiting factor not FB
  10. lendecatural

    lendecatural Smoking Fanatic

    Understand what you have and working with the circle calculator, you need a cord of 19 inches to get an area of about 60 square inches from my example above. Therefore, the height above the bottom of your CC for the firebox cut should be 4.6". If you put your RF plate a couple of inches above that, it will give you 5.4" above the the RF plate for your cooking grate if the grate is in the middle of your tank. Select Radius and Chord AB, use the area of your tank with radius of 12" and a Cord AB of 19 and you will see the OE length of 4.6". http://www.1728.org/circsect.htm

    Hope this helps. Good Luck and nice looking tank!

  11. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    NNS, Morning..... You are in good shape and ready to move forward with this build.....  The parts you have ready are excellent and will build a great smoker.....  

    Below are some drawings I put together for Alaska... the same size smoker you are building....    

    Your firebox is oversize but that is perfect... You do not need to adjust any dimensions in the build because of the over sized FB...  

    The Cook Chamber can only use so many BTU's for adequate heat and you have that covered nicely.... 

    Take your time and understand the drawings before you cut anything, to save having to redo stuff...  The number of food grates is personal preference.....   I would put the charging door for the FB on the front of the smoker...   the air inlets go on the end...   the lower air inlet can go on the bottom of the FB if you wish....   See Ribwizzards smokers for ideas of placement and design of air inlet adjuster (pie vents)....  

    I recommend inserting the FB to the welds on the CC... Set the top of the FB at 5.5" up from the bottom of the CC....  Connect the RF plate to the top of the FB....  extend the RF plate to 6" from the end of the CC...

    These drawings may seem confusing but take your time to understand them... I'm here for any questions as are others...    Dave

    ......Click on drawings to enlarge.....


  12. The calculator calls for 3.5 air inlets of 3"x4" .I can fit 3 on the side (see pic).could I make the same style on the bottom right below the others?
  13. On the door hinges.do I out then in the middle of the cut?
  14. where is your flange going to be?  Also, dont put it flat against the metal or any little piece of crud will keep the door from closing all the way.   Use the "tabs" to lift the hinge up, then weld on both sides of the tabs.

    Hard to describe, so tack weld it first and open and close the door, you will soon see what I am talking about.