120gallon build....just realized something and have gut wrenching feeling....

Discussion in 'Reverse Flow' started by dalematlock, Jun 27, 2016.

  1. dalematlock

    dalematlock Newbie

    So, I have a link on this build over on BBQ brethren (http://www.bbq-brethren.com/forum/showthread.php?t=229471), but discovered this website along the way, and I was already well along my way on this build. After reading through the tutorial the Dave has made many links to as well as the circle calculator. I think I identified a pretty big problem, but I'm hoping not. So, first off...here are my dimensions, and my calculations from Dave's tutorial.

    Propane Tank: 24" diameter, 68" long

    24 X 24 X 0.7854 X 68 =  (30,762) Volume in cubic inches / 231 = (133) Volume in gallons

    30,762  X 0.004 = (123) FB/CC opening in square inches

    30,762 X 0.004 = (123) Area under the RF plate in square inches

    30,762 X 0.004 = (123) Area required at the end of the RF plate in square inches

    30,762  X 0.33 = (10,151) minimum volume of the Fire Box

    30,762  X 0.001 = (30.762) FB air inlets in square inches

    Exhaust Calculation..

    Volume in cubic inches X 0.022 0.017  = [30,762x.022]=(676.764) Exhaust Stack Volume in cubic inches, above the CC.... (ESV) .. (The increase in volume ~30% shows a dramatic improvement in equalized temperatures across the cooking surface... edit 6/19/15 )

    ESV in cubic inches (.7854x6x6)= (28.27") Stack Length in inches
    0.7854 X Stack Diameter X Stack Diameter

    So, now onto the part that makes me sick somewhat. I was using Feldon's calculator initially and thought I had my Radius and diameter correct when I cut my CC/FB opening on my FB. I then discovered the circle calculator here and then realized that I needed to calculate for "Segment Area" not just merely diameter. As it stands right now my AB Chord is: 18" and the Segment height ED is: 5" giving me a Segment Area of 63.5, which on the above calculations I am supposed to be at 123!!!! Holy cow...Now I'm freaking out as I have already welded everything up thinking I was on the right track.

    It's an insulated FB, was a nightmare for me to fabricate, and now am dreading "Have I made a fatal error?". I could really use some advise on how to proceed forward.

    I have the Exhaust stack all mocked up ready for welding, the FB is fully welded up...the next step for me was to weld in the RF plate. But I want to hold off until y'all could lend some friendly advice. I'm crossing my fingers that everything should be fine and I can move forward.

    Please reference the above link for all of the pictures of my build thus far. If you need more pictures please let me know and I'll be happy to upload.

    Thanks again (It's my first build ever) So, go easy please, lol.

  2. jcbigler

    jcbigler Smoking Fanatic

    Judging from the pics you posted on the BBQ Brethren forum, it looks like your firebox to cook chamber opening may be too small. And the area of the cut out is about 50% of the recommended size.

    Not sure there is much good news here. I'll have to wait until I get home to check the numbers in the spread sheet. Maybe Dave will reply with some suggestions.
  3. socalcooker

    socalcooker Meat Mopper

    That's alot of cutting to change it. But if you weld the RF plate in and find out it doesn't work, it won't be worth it to try and fix it then. Personally I'd make the correction before you get so far you can't fix it. I've been reading so much about smokers before I start my build because I don't want to make a mistake. I picked this forum basically because of Dave's calculators and ribwizards builds. There's multiple guys on here that have multiple successful builds. I trust what these guys say. There's also some amazing fabricators here that could guide you through the best possible way to correct it.

    Good luck

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