330 Gallon First Build Help

Discussion in 'Reverse Flow' started by marlboro, Oct 4, 2014.

  1. I need some help figuring out my numbers for my first build...
    I have a 330 gallon tank which I understand to be 30" diameter and 114" in length... (I haven't actually seen it yet)
    anyway the guy supplying me with the tank has offered to cut the doors and fb/cc opening for us (we don't have a plasma cutter so we jumped on it)
    Just trying to figure out the dimensions and whatnot.


    CC size=80541.00
    FB recommended size=26847.00

    set the FB size so I get 100%

    FB/CC size=203.23

    RF plate area=304.845

    now the circle calculator I am not so sure on...

    with a radius of 15
    and a segment height of 9.9
    I get the segment area of 203.43

    with a segment height of 13.3 (rf height)
    I get the segment area of 302.54
    and a chord ab of 29.807 (rf width)

    This just doesn't seem right... if I use 1/4" for the plate that only leaves me a little less than 1 1/2" between my grate and the plate... I'm assuming I am doing something wrong.

  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Below are the drawings and calculations to make a pretty good smoker....

    ...Click on images to enlarge....

    The green area is the FB to CC opening you are going to calculate... It is also the area under the RF plate... ED is the height of the RF plate and FB CC opening... AB is the width of the RF plate...


  3. Thanks Dave,
    I am still confused though... I keep coming up with an ED of 13.3" or 14" depending on what numbers I run...
    Can someone please run the numbers and tell me what I am doing wrong?
  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Are you using the radius in the calculation.... that is 1/2 of the diameter....

    Click the dot for Radius and Segment height....
    Last edited: Oct 4, 2014
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    FB/CC opening 300 ish square inches.....

    Segment Height of 13" gives a segment area of 294 sq. in. .... chord AB 29 3/4....

    You can cut the segment height down a bit.... no problem in larger smokers..

    I think, maybe, the diameter needs to be checked..... you should be using inside tank diameter... you need to know the metal thickness and exact circumference to make the RF plate dimensions accurate... the tank could be 1/4" to 5/16 or 3/8" depending on age and when/where built....
  6. lendecatural

    lendecatural Smoking Fanatic

    Length is not your friend in this case, your length/diameter ratio adds volume and increases the height of the cutout. I found a post on here where someone sectioned a pipe and welded it back offset using the dropped piece as the firebox, it is not reverse flow, but you get the picture. If you don't need a smoker that big, it may be a way to go allowing for a lower cutout. If you cut 1/3 off the length, you would still have almost 5' of usable cooking surface.

    Last edited: Oct 4, 2014
  7. maple sticks

    maple sticks Smoking Fanatic

    Hi Marlboro, Not sure what your trying for. The calculator says 203.23 sq. in. FB to

    CC opening. Which using a 29" dia. with a 10" ED would give you (199.78) 

    If its a LP tank your using the CC is not 80541 its 76230. The ends are round.

    Good luck with your build.
  8. lendecatural

    lendecatural Smoking Fanatic

    You do need around 300 sq-in for a reverse flow smoker, especially for one that long to get proper flow. The calculator is set up to run numbers for offset as well as reverse flow but the recommendations here for reverse flow is that the calculator result should be multiplied by 1.5 to get good air flow.
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Me thinks you are using Feldon's calculator......
  10. maple sticks

    maple sticks Smoking Fanatic

    Hi Dave, Yes I was using the link from the first post. In my opinion

    if your having trouble with draft you increase the chimney. With that

    said I have never built a reverse flow so I don't know.
  11. I think Len is right with the length working against me...
    I ran the numbers with the end caps cut off roughly 82" in length and I get a segment area needed of 231.825
    The ED comes out to 10.9"
    Would that work?
    What would you guys suggest for the distance between the RF plate and the first cooking rack?
    If I cut my doors at 12 and 3 that would give me just under 4" still seems kinda short.

    Should I just go for a different size tank? I've looked on multiple sites and I've never seen anyone build out of a 330 gallon, aside from the one Len had referred to where they cut a segment out and basically made a 250 out of it.
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Feldon's has some inherent problems that have been well documented on this forum, and improved designs have been proven by many members building great smokers.....

    FB/CC and Area under the RF plate are insufficient, using Feldon's, for a Reverse Flow smoker....

    There are a number of threads, over the years, that document inherent problems and what and why stuff was done to improve on Feldons's... Feldon's was an excellent starting point.... a few tweaks and GREAT improvements were made.....
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    You are absolutely correct on the length causing problems.... The problem is.... increased surface area under the RF plate... that causes friction when trying to move air... especially when you are using "natural draft"... Short and fat is better than long and narrow... When building a smoker....
  14. lendecatural

    lendecatural Smoking Fanatic

    I tried to find a picture of the tank I saw on here that was sectioned, but I wasn't successful. If I had a tank that long, I would cut it at 1/3 of its length, get a piece of plate the width of the tank diameter, and weld the two back with the cut end dropped down using it as the firebox. you would end up with a football shaped FB/CC cutout so you would lose some area along the edges. The benefit for cutting a long tank in this manner is you save the time required to build the complete firebox, you just have to cut a wood door and put in vents. You are up against trying to get the air to flow a very long horizontal distance with the resultant friction losses as Dave pointed out and you don't want to put that much work into something and not have it flow well. Short and fat is a good thing for easy airflow; otherwise, you could consider using a BBQ Guru or similar forced air temperature feedback systems. There are some very reasonable priced systems out there. 
  15. boykjo

    boykjo Sausage maker Staff Member Moderator Group Lead OTBS Member

  16. lendecatural

    lendecatural Smoking Fanatic


    No, the one I saw had the cut off end welded back on and used as the firebox by using a flat plate between the CC and FB. It is hard for me to search the forum if you are looking for a specific smoker since I've forgotten the keywords that were in the post. I ended up with over a thousand posts to go through.....
  17. So I'm thinking I'll just go with a 500 gallon propane tank...

    Here are my new numbers.

    CC = 115500 cu"
    FB = 38500 cu"
    Stack = 1963.5 cu"
    FB Intake = 115.5 cu"
    FB/CC Opening (Area under RF Plate) = 462 cu"

    Diameter = 37"
    Radius =18.5"

    With a Segment Height ED of 16.5
    I get a Segment Area of 463.75
    Chord AB (RF Width)=36.783

    I am guessing from all the diagrams and drawings I have seen that the distance between the RF Plate and the first cooking grate of around 3" should be okay?
    Someone had said that is all a Lang has.  I just want to make sure everything looks right before I give the go ahead to start cutting...
    What is my range on Segment area? As in how much Segment area below 463.75 is safe?

    Thanks for all your help guys.
  18. lendecatural

    lendecatural Smoking Fanatic

    You should be fine with those numbers. The real problems come in when guys use Feldon's and don't factor in the reverse flow multiplier. Like Dave said above, it isn't so much of a problem on larger smokers since with a larger diameter, you have a more favorable length/diameter (read air friction) ratio. You can always add a baffle plate at the firebox entrance if you get a hot spot on the firebox end and you still wouldn't be dropping below 1.4 on the multiplier. The thicker the RF plate, the better...
  19. That's what I would do, go with a 500. Around here where I live, a 500 has not come for a reasonable price, but one of these days. There are problems with too fat of a tank. Access to the inside. Of course this can be over come. Pull out cooking grates and doors on both sides of the cooker. I believe about 30" diameter is more or less optimal for one side access. Less and you lose cooking area. This would be cooking for crowds. And I assume that's why you would go with the 500.   Just my humble opinion.

  20. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    One of our mods. smoker in progress..... boykjo


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