Newbie 120 Gal Trailer Build (Advice Sought)

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Original poster
Oct 24, 2016
Hey all,

New to the forum after lurking countless hours for the past few days. Tried to take as much as I could from other threads as an attempt to not clutter with yet another thread with questions asked a thousand times but in the long run this may just be easier. haha

I was able to rescue 4 almost brand new compressor tanks from the local ingersoll rand warehouse before they were given to scrap guys. So naturally I have to make a smoker out of atleast a couple of them. I own a welding/fabrication shop so I have all the means necessary to do this type of project, just not the knowledge which brings me here. Some pictures of one with the trailer I built.

I'm about 95% positive these are 120 Gal. tanks. (Dont see anything specified on the plate only going by what i see on their site) 

Diameter= ~24"   and the tip to tip length is ~68"

Now to the number crunching using the Feldon's calc and the formulas posted by DaveOmak ...

 CC Volume= 29,426.95 cubic inches(ci) (got this by using Dave's formulas which I think are more geared towards cylinders and not tanks. But figured going by the bigger number wouldn't hurt for this.)

FB Volume= 9,710.89 ci   (using the formulas again)

  - 23"L x 23"W x 20"H should give me about 10,580 ci (Feldon's Calc)

CC/FB Opening= 117.71 si (Formulas)

  -21" Length x 7.5" Arc Height = 119.54si (using a sweet simple calc I found online)

Inlets= 29.43 si (Formulas) (Haven't decided on square or round yet and placement)

Exhaust= 647.39 ci (6" pipe x 28.27") (Formulas) Feldon's gives 529 ci which is 18.72" for 6" pipe

The plan is to do the RF plate right on top of the FB on the inside. Haven't seen any specifics on the location of this though. In my sketchup drawing it'll put the RF plate at about 8.18" from the bottom of the tank. 

I haven't cut into the tank yet so anything can be changed.


1) How do the numbers look? Just kinda looking for a second opinion/double check.

2) We're dabbling in the idea of a removable RF plate so we can put a grate in for grilling as well. Thoughts?

3) What are some of the "if I could do another one, I would do this..." type things do you guys have?

4) What do you guys recommend for the intakes? I would like to do one (or more) above and below the fire grate.

5) Will people in Southern California even know what a smoker is? People around here don't even seem to have the time to wait for their coffee maker. And it shows when they expect ridiculous time frames on projects.

Thanks for your time.  I appreciate anyone who's made it this far and welcome any input into this project. I'm sure I'll have more questions soon but that's all I can think of currently.
Hi, my build is similar to yours,but a propane tank. You need to use the inside dimensions of the tank for your calves. I used Dave's calculator. If you use a removable baffle, how will you attach a drain pipe? There are tons of smokers in SoCal and lots of competitions. Check the KCBS roster. I am in Baja and smoke for a couple of restaurants.
I cut one end off the tank flat so that I can add a warming cabinet on top of the fire box. According to Dave, you use 1/2 the column of the domed.end. for part of your cook chamber column calc
Finally got some progress on my build. We are trying to do most of the welding outside on the tank before cutting the door to prevent it from getting too bent out of shape. 

Biggest fear I have right now is that I put the bottom vents on the firebox too low. There's about 1.5" from the bottom of the fb to the bottom of the vents. Didn't take into account ash build up but if worse comes worse I can cut a portion of the fb out and make it lower. 

Working on the plenum and stack right now, just waiting for the plenum to cool before I put it on the tank.

Now for the pics...

Biggest fear I have right now is that I put the bottom vents on the firebox too low. There's about 1.5" from the bottom of the fb to the bottom of the vents.

Hi BraveSirRobin. I really think it'll be fine. In mine, my fire doesn't even come close to the sides of the FB. No ash should collect that far to the side. And this way your air is coming in from under the fire. Looks great so far!
I have the same tank.. I am about 90% complete on my build.... I too have removable RF plates... I like your idea of removing the RF plate and using it as a grill ... I'm just hoping the heat at the FB end doesn't warp the plates ...
Finally got the cc door cut open and hinged. Just need to add the rest of the flat stock and a handle. Just need to figure out what to do with the handle. With this being on the trailer and me being 6'1" it's perfect for my reach when the door is open. For my 5'7" neighbor, not so much. Haha. And of course we made the storage boxes on the side an inconvenient heigh. But that's a battle for another day.

An update since its been a while... Its done! (Pretty much)

After doing a inaugural smoke a few things I need to do:
-Need to add a second cooking rack, if I feel like it.

-Need to figure out the gauges, 20° difference from one side to the other. Catch is, it was hotter on the side furthest from the firebox. Leads me to believe its the gauges.

- Need to install a gasket around the door. (Bought it, just haven't put it on.)

-Need to make a firebox grate to use more coal and less wood. And keep things a little more organized in there.

-I actually had fun with the whole process of smoking. Got some pork ribs the night before, applied the rub, let em sit over night, threw them in the smoker, made a pen while periodically checking. Enjoyed with a couple close friends. Even if the ribs were a little under cooked.

Finished Product-

Ribs on-

The pen I did because why not? Haha
I do not believe they are adjustable but I'll double check. I used a digital thermometer in the cook chamber while it warming up to see how close they were. It seemed to be +-10° with that if I recall correctly. I have a feeling I'll be shoveling out more cash if/when I get more serious for finer instruments.
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I bought these thermometers off amazon and looked them up, they're not adjustable. I'll have to look into the ones you suggested. I bought a wireless probe from wal-mart for $15 and it seems to work well for the time being but as most things from wal-mart, I question its longevity.

I do plan on selling this smoker since I have the tanks to make more. Perhaps on the next one I'll go all out, at least as far as my budget will let me. is reader supported and as an Amazon Associate, we may earn commissions from qualifying purchases.

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