1st Smoker Build - 300 gallon Reverse Flow

Discussion in 'Reverse Flow' started by mschilling57, Sep 17, 2017.

  1. Well I am excited to have finally started my first smoker build. I haven't been much of a "forum" guy in the past, but thought SMF looked like a fun and educational tool while building my first smoker! I am excited to be here and look forward to any advice and help along the way. I have been wanting to build a smoker for awhile now, but have shy'ed away due to not being educated in the smoking world. I am ready to dive into it and get started now though!

    Today I picked up a 300 gallon fuel tank and an old pop-up camper frame for my build. That's all the further I have gotten today mechanically. Since arriving at home, I have started to calculate all of the dimensions on my smoker utilizing several forum posts, especially DaveOmak's, thanks Dave! Attached is a picture of my smoker plans, everyone can give it a look and see what they think.

    I will post pictures and keep everyone updated through the entire build as I have found that helpful from others while designing my smoker. I am planning a reverse flow smoker as you can see. 

    I am also trying to put together a budget right now and don't have a ton of money to throw at this smoker (college student, however about to graduate!). My budget is $400, can it be done? I already have access to all of the fabrication tools like a welder etc. I am going to price some materials locally, but if anyone would be willing to share their metal prices (angle iron, square tubing, expanded metal) that would be very helpful to make sure I am getting a decent deal.

    Thanks for all of the help and I hope I can learn as well as help others with this build!
  2. Here is the trailer and fuel barrel. I haven't cut into the barrel yet but I'm guessing it's pretty thin metal. I know a propane tank or something of that sort would have been best, but I didn't want to spend $250+ on the CC itself. Also, Traeger's and other grills get as warm if not warmer than this CC will ever get, and they are made of pretty thin steel (might be off base here, just a thought). Snagged the barrel for $30 and the trailer for $50. I will likely have to move the axle back on the trailer, we'll see after I get things situated on there. I'm going to cut off the outer edges of the frame so the entire trailer sits between the wheels. Also will obviously add fenders and lights. At this point, I'm thinking I'll make a frame and raise the CC up off the trailer floor since the trailer already sits low from the torsion axles. Also that way my firebox won't have to sit below the trailer floor level, I have never been a fan of that design. Thoughts and opinions??

  3. ahumadora

    ahumadora Smoking Fanatic


    Yo may have to watch the height of the cook chamber otherwise unless you are 7' tall you will not be able to open the door all the way.

    When cutting the cc door out you probably will want to reinforce the door as it will be flexible.

    Rotate the tank so you don't have the weld seam in the middle of your door.  

    keep us posted
  4. Yeah, with the torsion axles this trailer sits pretty low so height shouldn't be much of an issue but I will watch it. I was just going to reinforce the door by making a frame out of flat strap iron and welding it around the edge, would you recommend something else? And yeah I'll definitely be placing the seam at either the top or bottom of the CC. Thanks for the feedback!
  5. Here is an example of what I was thinking of doing with the door.

  6. radioguy

    radioguy Smoking Fanatic


    Welcome to SMF. You may want to blind weld your door flange. I think they look better.

    good luck

  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    That should make a very good smoker...   Nice trailer...   Blind welds below...  

  8. Have never thought about blind welds, that's a good idea. My main question right now is how to figure the exhaust stack size. I think I did my calculations right; however, I am unsure how they fit my particular smoker. By this I mean, if the formula is 0.7854 x stack diameter x stack diameter, how is that unique to my build? If you want stack length to come out to around 36", I'm showing that my stack should be around 7" in diameter and about 38.5" tall, but that's just working with the formula and has nothing to do with my 68,500 cubic inch smoker. I guess what I'm asking is how does this formula create the correct exhaust stack volume for different sizes of smokers? Hard to explain what I'm trying to get across, hope it makes sense.

    Something else I thought of today, how many of you have a firebox welded to the main trailer frame? I'm guessing there isn't enough heat to transfer very far onto the frame?

    Thanks for all the help so far, I'm definitely a newb!
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Volume in cubic inches 68,500 X 0.022 0.017 = Exhaust Stack Volume in cubic inches,    1,507 

    ESV in cubic inches  =____1507_________________________ ... = Stack Length in inches (36" +/-) = 39" height

                                         .7854 x  (7")stack diameter x (7")stack diameter

    The adjust the diameter to meet the height of 36" +/-
  10. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    BTW.....   0.7854 is a short cut to......    ¶ r²...    =  0.7854 D²
  11. Ohhhh I gotcha now. I was making it harder than it needed to be, was reading the text formatting incorrectly. Correct me if I'm wrong, but the formula is as follows:

    Stack Length in Inches (36+/-)  x  .7854  x  stack diameter  x  stack diameter

    So the way I understand it, you plug in numbers close to 36" for stack length, and also plug in numbers for stack diameter, and once you get to your ESV you have reached your desired measurements? What is the reasoning behind the 36"?

    Thanks for the help Dave!
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    ESV is already calculated....    CC volume X 0.022 = ESV...   then you calculate for the exhaust stack diameter with a parameter of +/- 36" height..... (30-40")

    Alien and his buddies is where all this started...  In the calculator they put together, which we here at SMF altered, they found that....  

    Enter the diameter of your chimney pipe to find out how long it should be.
       • A chimney that is too short may produce insufficient draft (drawing of air). A chimney that is too long may cause the air to cool before it exits, reducing effective draft and worse, dripping of exhaust materials onto food!
      • Many horizontal smokers have an exhaust between 30-40 inches in length, but there is no hard and fast formula.

    Without going through all the testing they did, I figured they were on to something that is pretty much a given in the industry...  length matters...  and they described the boundaries they limited the builds to....  
  13. Awesome, makes sense! Thanks!
  14. Just ordered my trailer light kit, fenders, safety chains, wheels and tires! Getting excited!
  15. radioguy

    radioguy Smoking Fanatic


    I recommend not welding the firebox to the trailer frame over a long distance. That fire box will want to move with heating and cooling. Overtime welds will fail. If you need to attach it, over a long length bolted, slotted holes. You can weld braces, tie points. Just remember that box has to expand / contract.

    A friend of mine has a Lang where the rear of the Firebox is welded to the trailer frame for the entire width of the FB. The firebox verticle welds are cracking above and below the attach point.

    It will work but you may be repairing it in a few years.

    Last edited: Sep 20, 2017
  16. Thanks for the advice RG, glad to hear some personal experience with the situation. I witnessed another smoker built by a fuel tank the other day and everything seemed to be fairly sturdy, although the door did seem to be rather bowed out from the heat, granted they were burning it out for the first time when I saw it (very hot). Any recommendation on how I could strengthen that lid so it doesn't bow? Leaning towards maybe an "x" frame on the back side. 

    Also, they just used the firebox to burn the whole thing out for the first time. Anyone do it differently like put wood directly in the CC just to burn it out for the first time? 

    Thanks for all the help, my design is getting better! A propane tank would've been ideal obviously, but on a budget and the $30 fuel tank vs $250 propane tank seemed like a no-brainer for me. 
  17. Been making some progress this past week. I have gotten the trailer cut down to the dimensions I want (I think) and also made some great progress on the CC. I picked up a piece of 1/4" steel and have built the reverse flow plate out of that with a piece of angle iron down the middle to act as a grease tray. I cut my door with a plasma cutter and then just used strap steel to make a frame. I also acquired an old water pressure tank (80 gallon I think) to use for a firebox. It may be slightly undersized, but once again, I'm on a budget and it was free and pretty dang close to the size I needed. I will snag a picture of it soon.
    Lid.JPG RF plate 1.JPG RF plate 2.JPG

    One question I have is what are some of you guys using for counterweights or latches to hold your lid up? I can't cut pieces at any more of an angle than 45 degrees so it makes it hard to create a counterweight like I often see.

    I hope this thread may be helping anyone who is looking to build their first smoker as that's what it's purpose is! If anyone has any questions or would like any particular pictures don't hesitate to ask!
  18. Made some pretty good progress today. I got the fenders welded on, cut the hole for the FB to enter the CC, and also fabricated and welded in the guides that the grate will slide on. This way I can pull the grate nearly all the way out and it will still stay relatively flat and not fall forward. Next step will be getting the CC and FB to mesh together and get them mated and welded up!
    . FB to CC opening.JPG Fenders.JPG
    Grate Slides.JPG Grate Slide close up.JPG
  19. ahumadora

    ahumadora Smoking Fanatic

    You will want to get that door sealing better than that. All the calculations go out the window when you can drive a bus between the lid and cooker. breal out the chain and bottle jack

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