150 Gallon Smoker Build.

[Mr. Mohon]

Hi All. I am starting an offset smoker build out of a 150 gallon propane tank for the cook chamber and a 80 gallon propane tank for the firebox. I finally got the second tank today so now it is design time. This is my first smoker build. I am planning on designing this whole build in CAD before I even start building. Got to keep busy during this Shelter-In-Place. Plus I want to make sure that I get a full materials list before I start building so I can order all the material at once and only have one delivery. I really like the one that 45 acp did back in 2013 (here is the link). Post #19 shows the final build. I am also gearing towards an Aaron Franklins style cooker so you will see some stuff that resembles the way he builds.

Cook Chamber 150 Gallon Tank Dimensions:
84" Long X 24" wide

Firebox 80 Gallong Tank Dimensions:
64" Long X 20" wide

Im planning to cut both ends off of both of the tanks and weld flat plate to the ends. Im planning to cut the cook chamber down to 60" long and the firebox down to 30". I am also wanting to make the firebox oblong vertically so I am planning on cutting the firebox horizontally in half and welding 6" flat bar in to make it oval. This would give me a cook chamber of about 15.6 cu.ft. and a firebox of about 7.6 cu.ft. FYI, I am aware of Feldon's BBQ Pit Builder Calculator. I plan on putting it on casters like 45 acp did and not on a trailer like most people do.

I do have quite a bit of questions though. Here are some in no particular order:
1) Why does everyone start with cutting the doors first? I would think to marry the two chambers first and then build the legs before cutting the doors.
2) Gauges mounted on the door or mounted on the chamber itself and why?
3) Tuning Plates. How big should tuning plates be. How far above the firebox opening and below the grill grates should the plates be? Does there need to be a baffle from the firebox to the cook chamber if there are tuning plates. Cant you just push the first tuning plate all the way up against the side of the chamber and that act like a baffle?
4) How big should a firebox door be? I'm not talking about the air intake opening I'm talking about the door itself that you would open to add more wood. Is there such thing as too big of a door?
5) What is a good/average grill height? Im meaning the height from the ground to the bottom grill rack.
6) How big of a shelf do you guys like? How deep? How far below the door is a good location so that the door does not hit something sitting on the shelf?
7) Chimney Size preferences? I was thinking 6" pipe. What do you guys recommend/like?
8) Is there such thing as too big of an opening from the firebox to the cook chamber.

This is what I have in mind so far.

I will likely have a lot more questions so get ready. Thanks for all of the help in advance.

 

[SoutherPawrookie]

The render of your pit looks good. I am building a similar pit with 3/8 " x 24" x 72" cook chamber and a 3/8" x 24" x 24" fire box. I am fairly new to this as well but I do know that 40" grate height from ground is too high. I settled with 37" and because I felt other pits at 32" 34" was too short. I also went with a 5.5" x 40" smoke stack

 

[howyegettinon]

building my own very similar to this, would love to see some of your questions answered

 

[Landiesel]

I just finished mine using 3/8" pipe CC, 1/4" plate, and some Frankensteined parts from a cheapo smoker left on the side of the road and might be able to answer a few of the questions from my digging on here and doing myself:

1) Why does everyone start with cutting the doors first? I would think to marry the two chambers first and then build the legs before cutting the doors.
I think you could certainly do this; out of convenience and lack of real shop tools, I attached CC pipe to legs first and cut the door first so that I'd have access inside the chamber to help in attaching firebox and other cap plate on smoke stack end
2) Gauges mounted on the door or mounted on the chamber itself and why?
I attached to door bc I intended to have probe right where I'd be cooking the meat right above grate, last 1/3or 1/2 of the chamber for standard offset and doing pork/beef. (Made the mistake of laying a brisket right near the door where the probe sits inside the chamber when closed, though, which obviously through off the gauge haha don't make that mistake)
3) Tuning Plates. How big should tuning plates be. How far above the firebox opening and below the grill grates should the plates be? Does there need to be a baffle from the firebox to the cook chamber if there are tuning plates. Cant you just push the first tuning plate all the way up against the side of the chamber and that act like a baffle?
I do not use tuning plates but have an angled baffle welded inside the CC to deflect smoke downward and prevent the direct radiant heat from the fire itself (like sitting next to campfire). You just want the convective heat from the smoke, so should reduce any line-of-sight connection. You're idea about the tuning plat up against the FB should work assuming it's above the opening and below the cook grate
4) How big should a firebox door be? I'm not talking about the air intake opening I'm talking about the door itself that you would open to add more wood. Is there such thing as too big of a door?
Door can be as big as possible I imagine. Because mine's a bit smaller I just needed it to be as large as possible to make putting in logs easier and messing with fire
5) What is a good/average grill height? Im meaning the height from the ground to the bottom grill rack.
As a residential architect, a good operating height for standard counters (think your kitchen counter at home) is 34"-36" above floor, which is what I based mine on. I have welded in angles for a smaller top grate on mine as well, which I haven't fabricated yet, but they can be whatever height I suppose
6) How big of a shelf do you guys like? How deep? How far below the door is a good location so that the door does not hit something sitting on the shelf?
I don't personally have a shelf so may not be able to answer the best, but I'd imagine deep enough to fit a standard baking pan loaded with a monster brisket and not tip over.
7) Chimney Size preferences? I was thinking 6" pipe. What do you guys recommend/like?
Mine's a 4" diam. and height I got through Feldon's but I feel like there's a great deal of back pressure so wish I went with something like 6" like you're saying
8) Is there such thing as too big of an opening from the firebox to the cook chamber.
I think the idea of the throat between is to allow at the same time enough exchange of convective heat from the smoke, while limiting the direct radiant heat given from the flames and any surfaces it heats up. My father-in-law has a smoker with the firebox integrated inside of the cook chamber itself, but it is ripping hot on that end while being deathly cold on the other.

Hope this helps