First 120 gallon smoker build

Discussion in 'Reverse Flow' started by navarre, May 17, 2013.

  1. I now have 2 120 gallon tanks for smokers. I am thinking of building the first one as a permanent installation, and the second as a trailer mount. 

    I live in Navarre, FL near Pensacola. It is hot and very humid most of the year, and I am essentially at sea level. We smoke wild hogs, brisket, turkeys, chicken, game hens, sausage, most anything that will fit in the smoker. We also do seafood boils, and grill oysters, fish, etc. 

    I have been doing some more thinking about the smoker. I plan on using charcoal for consistency instead of wood for the most part. A coworker does some amateur comps, and he recommended using the DigiQ and two 25cfm fans. I am thinking of using the A-MAZE-N smoker of some type for flavor. 

    Have some questions about the firebox, water, etc. Where would the best place be to put the water pan? I am thinking of a permanent pan of some sort with a fill tube and a small drain at the top that would tell me when it is full.

    How much charcoal would I be looking at using for boston butts or large pieces of hog. We often quarter them, or if they are small toss them whole on the smoker. How would I refill the charcoal, if you want to burn from top down?

    I may build the firebox from scratch and not cut the end off the tank to make one. I would like to have a warming box with rails/shelves to put standard steam table pans in. I just acquired another 120Gal tank, so I am thinking of making this one permanent in the back yard. Could I make a firebox from block and firebrick and pipe the heat to the tank?


    I have a trailer to for the second smoker already,We go camping with a large group (20+) frequently, so this will be the ticket. 
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I would build both exactly the same...  Standard firebox, sliding shelves....  If you build an external block FB, there will be significant heat loss...  Use the calculators to determine dimensions.... I recommend building the firebox a couple inches wider than the reverse flow plate for easy fitment and build....   The circle calculator will tell you the FB / CC opening, RF plate width and how far above the bottom of the smoker to place it.....  If you need help, I am here.......    Dave

             /Pit Calc/Circle Calc/
    Last edited: May 17, 2013
  3. circle calc is interesting. Not sure how I would use them. I saw something on one of the forums on how to make a pattern on a pipe so that the resulting cut matches the tank. Cant find it now. How do I determine the width of the RF plate? Wouldn't it be just above the inlet to the smoker? 

    Why would a block firebox cause excessive loss? It would be ducted in to the smoker and insulated. 
  4. radioguy

    radioguy Smoking Fanatic

    The pit calculator will give you the area of the FB to CC opening, based upon your tank size and firebox size.  Since you are dealing with a round "D" half-moon opening then use the circle calc to find the right size opening.  Input your tank radius and then move the segment height until it is the same as the FB to CC opening area.  This will give you the dimensions of the FB to CC.  Your RF plate is determined by making its height 1.5 times the FB to CC area. 

    Here is a link to one of my many questions on the RF plate and firebox opening, Dave did a great explanation here:

    I hope this helps you. 
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    A block FB has a lot of thermal mass..... it will take a long time and lots of wood to get up to temperature.... then the ductwork going to the CC will lose heat....  also sealing up the block firebox for proper air flow will be a bugger....   a proper RF smoker needs to be air tight to work properly, or close to it.... 

    In the circle calculator, click on Radius and Segment Height ED

    Enter the radius in the box....   adjust the segment height until segment area matches the CC to FB opening from the Feldon Calculator...   That segment height is how far above the bottom of the CC the cut needs to be made for a proper sized opening  that matches the circumference of the tank (cook chamber)... then adjust the segment height again until the segment area you get is 1.5 times the area of the CC to FB opening... that is the height above the bottom of the tank the RF plate should be installed.... Then, chord AB is the width of the RF plate...  It is important to have fairly accurate measurements for this stuff, as you can probably tell..... 

    All of this is confusing....  practice using the calculators until you think you have a number that is correct.... Post your findings and we will help....  When you figure all this out, you will be a Smoker Building GURU and impress your friends explaining how you figured it all out....  

    If you need help, I and others are here to help....  It is rewarding knowing how all this stuff fits together....  PM me anytime.....    


  6. DaveOmak    is very correct, My advise is....if you want a brick smoke house , build a brick smoke house. They are some great designs out there and they are the bomb to cook on. But if you want a reverse flow smoker, build a reverse flow smoker. You can insulate the firebox and the cooking chamber, but I would not recomend trying to build a cross between the two. The reverse flow needs to be very air tight and steel and brick expand at different levels when heated, and I believe this would be a constant fight keeping it sealed.

    Easy way to match the firebox to the cooking chamber is just build the firbox 1/2 inch or so larger than the cooking chamber, now all your worried about it cutting striaght lines at a 45* angle to each other.

    You know, I have a 36" wide' 32" deep 42" tall cooking chamber with 6 racks just sitting in my garage. ( 3/16" thick) I always though it would be perfect to set inside of a fire brick build. let me know if your interested. Get it to you real cheap.
  7. I agree with Dave and Ribwizzard.  I am just finishing twin smokers.  You might think of building an insulated firebox to conserve feul.  I'm not into a fixed firebox, it limits your options, not to mention points brought up by RibWiz.

    Hvae more questions, be sure to ask.

  8. Got pics?
  9. [​IMG]
    My crappy attempt at drawing. Thinking I will have the chimney welded to the warming box, and a small opening to the warming chamber for a bit of smoke to season some foods without total immersion in the cook chamber. Your thoughts?
  10. Nice pics urbotrimm. Still getting things/ideas together for my smoker. I attached a pdf that sort of shows what I am thinking of doing. I think I will leave the tank intact and just cut holes for air intake and exhaust, and of course doors. I still need some ideas on where to locate the water pans, and a smoke chip pan if necessary. I think I will install a propane burner in the cook chamber to preheat and provide additional heat if necessary. Don't need to use it as a grill, since I have one already. For vents in the firebox I will make some manual ones the proper size, and an additional one for a DigiQ or similar that will be plugged when not in use. 

    I picked up a heavy duty trailer with a mobile home axle on it for $200 yesterday. It is 6x8. 

    Gotta pick up the second tank this weekend, and go look for steel at the local scrap yard. 
  11. [​IMG]
    Trailer was $200. One tank $70, other free. Materials for smoker about $100.

    Cut for firebox took 9 harbor freight cut-off wheels. 3 broke when I got close to finishing cut. 

    1 pair of shorts and 3 cuts on leg when grinder took off out of my hand when wheel got stuck... priceless.

    I am going to attach firebox directly under smoker, and have it overhang the side of the trailer a few inches to facilitate cleaning ash, reloading, etc. I am building a 10x10 box to connect the two that will have a damper installed. 
    I have some 1/8 inch steel (the upside down table on the trailer) that will be enough to make a warming box. A little thin, but it is available. 
  12. Don't forget pics.  Anxiously awaiting your build.
  13. oldschoolbbq

    oldschoolbbq Smoking Guru OTBS Member

    Don't know why I stop on these Post, I know Trish won't let me have anymore big toys. I guess it's the old Welder in me , but I love to look.

    I'll be in for the ride [​IMG].

    Remember one cut , no do overs.

    Have fun and as always. . .
  14. Going to light the torch this week. 

  15. picked up some bar stock, and flat stock. 

    Have some questions for you. I am thinking of making the top cut for the lid, weld the hinges on, and then weld flat stock for the seal. Second make the side cuts, and weld the flat stock, then the bottom. Will this be a good idea?
  16. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    A good idea is to draw everything before you start....  Welding up mistakes is fairly easy, but why do it...  plan out the entire smoker on paper... doors, air inlets, grates, stack and plenum.. etc.... erasers and new lines beats rewelding a mistake by TONS...

    Build the firebox the width of the CC... 24" in your case.... build it 25% bigger if you want...  than Feldon's says to and don't worry about adjusting for the larger size... extra size is for more wood and ash storage and doesn't enter in the equation of heat management....  build the door to the FB on the front side where you will be cooking.... add the air intakes on the end... Feldon's recommended air inlet 5" up from the bottom, or so.(horizontal pie vents)....  a second air inlet across from the opening to the cook chamber for moving heat into the CC from the FB and make the area of that  opening 10% of the lower opening, using a horizontal pie vent... (looks like a bow tie).....

    The firebox to cook chamber opening should be 5.5" segment height and the curve should be a 12" radius....  same as the tank... 

    The RF plate has a segment height of 7"... a width of 21.5"....   and 7"+  should be left open at the end of it for air, smoke, heat flow...  

    Removed the info....  PM me if you would like a copy of it......    Dave
    Last edited: Jun 2, 2013
  17. I have it sketched out with dimensions. My thought about the firebox to CC connection was to cut a 10x10 hole in each, and join them with a box a couple of inches tall with a damper installed. It matches up with Feldons calcs. I want to make rectangular vents for the firebox vice round ones. Easier cutting. I have an ashbox door from an old stove to install on the end of the FB.  
  18. jubilee847

    jubilee847 Newbie

  19. On my build I took and had everything planned and had door laid out on cc. Marked where I wanted my hinges. Went ahead and speedy cut those areas then welded hinges on which ensures that door won't shift any when you finish cutting. After that I cut the rest of door out leaving just an inch or so on each side. Next I tacked bottom flat bar on to keep door from falling in. Finished cutting door and then tacked the rest of flat bar. Made sure it all worked right and welded it up

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