Vertical/ Horrizontal Back Porch RF Smoker Build from 2 100lb propane tanks

Discussion in 'Reverse Flow' started by tim king, Jun 2, 2016.

  1. tim king

    tim king Newbie

    Hello All,

    I'm new to the forum and to smoker building but I'm anxious to get started. I have wanted to build a smoker for several years but have not had the funds. I have about decided that I will never have the extra funds to build the smoker trailer of my dreams, so I'm going to do the best I can on a low budget and still end up with a serviceable reverse flow smoker that should be big enough for my family and friends. I have no aspirations to be a competition pit master, I just love smoked meat and there are no good BBQ places within several hundred of miles of where I live in South Dakota. Therefore I'm taking matters into my own hands and building a smoker. 

    As this is a budget build, I'll be using whatever I can find cheap for the parts. This budget requirement has led me to my design. Form usually follows function but in this case form follows frugality. I came across a free 100lb propane tank and then another one for just $25 so I've decided to make a vertical/ horizontal, reverse-flow, smoker in the shape of a "T" set on its side. I took some time and did the math and I think I have things figured out about right but I've never built a smoker before and could use some advice. 

    Here are my numbers (assuming the volume of a 100lb propane tank is a true 25 gallons)

    1. Cook Chamber volume 8,663 cui ( this is one full tank and half of the other one)

    2. Fire box volume 2,888 cui ( the bottom half of the vertical tank)

    3. FB to CC opening 35 sq in

    4. Vent opening 10 sq in  (top vent 3 sq in bottom 7 sq in)

    5. Exhaust stack volume 191 cu in

    6. Exhaust stack size 3"x 27"

    7. Area under Reverse flow plate ?

    8. Reverse flow opening to upper chamber ?

    I have a question regarding the reverse flow plate and plate opening to cooking grates. The page I referenced to obtain these numbers states that the calculation for the area under the RF plate and the opening are the same as the calculation for the opening between the FB and CC. This yields an area under the RF of only 35 sq in or 5"x7" that seems way too small. Am I confused about what the area under the RF plate is? If I make the RF plate that small the opening to above will be over three feet long... Should I ignore the area under the RF plate and use this calculation for the opening between the RF plate and the cooking surface only? 

    I also have a couple questions regarding the vertical side of the smoker...

    1. Does the opening from the CC on the Horizontal to the CC on the need to equal the FB to CC opening? Or should I just cut the opening the entire size of the upper CC above the RF plate?

    2. I would like to be able to close off the Vertical section, if at all possible, so my thinking is that a smaller opening like that of the FF to CC would be easier to close. 

    3. Does the exhaust stack being centered on top of the vertical tank affect its drafting characteristics and as a result its size?

    4. Should I make two exhaust stacks one on the horizontal and one on the vertical? If I make two I would reduce the size of the stack on the horizontal tank to reflect the smaller CC of the closed off vertical chamber.

    5. Is there a good design for a damper that works on a curved surface like the side of a vertical tank?

    6. Is there a good trick to notch the horizontal tank to fit the vertical tank? I made a cardboard template but tracing it onto the curved tank was difficult. As a result my notch is pretty ugly and has some bad gaps.I might have gone too far already and will have to just keep fitting it up and trimming little by little to get a good fit...

    7. What is the best way to deal with draining off drippings? Should I just let them drain to the bottom and put a drain hole down there? Or should I make a dam on the RF plate and put it on a tilt so that it can drain out the front or back?

    Sorry for the bombardment of questions this is my first smoker build and I'm learning as I go.
    Last edited: Jun 2, 2016
  2. aussiq

    aussiq Smoke Blower

    I can answer the last question for ya coz thats a easy one. Put a dam in your rf plate with a hole so everything has a slight slope to the hole. Then weld a pipe with a threaded end through the bottom of the cook chamber and to the hole you have in the rf plate. Obviously the threaded end is on the outside of the cc where you can screw on a ball valve which you can drain when needed
  3. tim king

    tim king Newbie

    Thanks I have seen a couple designs since my post and have done my best to get things in the right place.
  4. tim king

    tim king Newbie

    Here is my progress so far.
    I notched the horizontal tank and put it on legs.

    I marked out and cut the door on the horizontal portion, welding the hinges on before cutting the whole door loose.

    Next I fitted the vertical tank to the horizontal as best I could.

    I had to cut and scab back in a piece of the notch I had removed.

    I then cut and fitted the reverse flow plate and used it to mark the location for the opening between the firebox and the cook chamber.
    I cut out the opening and set the rf plate in place.

    I then cut the doors on the vertical tank following the same procedure as the horizontal tank. One on the lower half for the fire box and one on the top for the vertical cook chamber.

    I then welded the RF plate in position. It took a long time and about half a box of welding rods because my torch cut was so jagged and there were lots of voids to fill.

    After that I cut a circle of plate steel and welded it in between the fire box and the vertical cook chamber. I rested this plate on the portion of the RF plate that extended into the fire box.

    Next I made a frame for the cooking grate of 1" square tube steel. I welded 1/8" expanded metal to the top of it and clamped it in the spot where I wanted it. I then cut angle iron to fit and welded it into place under the frame of the cooking grate.

    I then cut a few pieces of 1" square tube at a 45 and welded three of them together to make a handle for the horizontal tank. After the handle i added some big box store temp gauges and decided to season it.

    I also cut off the threaded collar on the top of the vertical tank and welded in a short section of 3" pipe I had laying around.

    Unfortunately I ran out of time and, having promised to smoke a brisket for Father's Day, I had to get the smoker operational ASAP. With no time to make a proper vent I just shot some holes through the door of the fire box with the torch, dropped a scrap of expanded metal in the bottom and lit a fire in it.

    So far the smoker is working. I have no latch on the doors and no handles on the vertical doors. I need to trim all of the doors to seal the smoke in. I also need to fashion some latches to keep the vertical doors closed and a counter weight to keep the horizontal door open.
    Last edited: Jun 19, 2016
  5. smokinal

    smokinal Smoking Guru Staff Member Moderator OTBS Member ★ Lifetime Premier ★

    Looks like it's coming along quite well!

  6. tim king

    tim king Newbie

    Here is the progress as of now. It is almost finished, all I need to do is make some supports to hold food grates in the vertical cook chamber, along with a handle for its door, a handle for the fire box door, and add a blower attachment to hook up the flame boss temp controller.
  7. tim king

    tim king Newbie

    Here it is with the doors open, showing the charcoal basket inside the firebox.
    unclebubbas bbq likes this.

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