New smoker build

[maineman]

Hi all, I’ve been lurking for a while trying to learn and come up with a good, functional design. I want to build a small smoker/cooker from a 130 gallon fuel oil tank. It measures 26”wide x 33” long x 42” high. I would like to use a rotisserie rack in it with a firebox and reverse flow set up. I figure I need about a 40 gallon FB. That’s about as far as I’ve gotten, going to get cranking this week. Any input, thought, or suggestions are greatly appropriated.

 

[mike243]

I have a 250 gal smoker almost completed, I layed it down and cut a door from center to center, right now I have a 55gal drum as a fire box, I used self tapping screws to secure it, I wanted a 30 gal and they didn't have 1 but will replace it after I finish and start cooking with it. I would rather have to big a firebox vs too small imo I know the firebox wont last long so that's why I screwed instead of welded.

 

[maineman]

So I have been thinking long and hard about this build before doing anything. I think I am now going to use a 275 gallon tank. I figured I might as well build one that can do a whole hog. I have two different 275 gallon tanks available to me. One is vertical and the other is horizontal.. the horizontal seems like it would be nicer because it would not be too high but I'm not sure there is enough room in it to make a whole hog reverser flow smoker/cooker.
Has anyone made a whole hog reverser flow cooker that could share some pictures or suggestions? Would I be better off using the vertical tank? Lastly, what is the best door cutout design? Will the tank shape change when I cut the door opening, if so how do I prevent it? I’m sure I’m going to have many more questions as the build gets going so I’ll say thanks much in advance for any direction or advice!

 

[maineman]

Bump with a dumb question. What is the minimum size needed to cook a whole, butterflied hog no bigger than about 100-120 pounds(length, width, height). We might do a whole hog once a year but will use the cooker for other things more often. I’d like to keep as small as possible but still have room for the whole pig. Thanks much

 

[kmmamm]

40 years ago I thought it would be smart to go against conventionality and build a horizontal hog roaster out of a 275 gal fuel oil tank. My reasoning was that the lower, horizontal design would be easier to load/unload 240 hogs. Additionall, replacing the rotisserie with a stationary grate would provide more real estate for larger cooks. The result was a pretty sleek looking unit that loaded easily and could hold a lot of stuff. It only took one hole hog cook to realize as a rotisserie hog roaster the design would work, just not very well. The shallow wide cooking chamber didn’t heat as efficiently as the tall narrow verticals I had built previously. As a result, cooking time was longer, it used more fuel and flare-ups were pretty interesting. On the other hand, with the large stationary cooking grate installed, it was perfect for roasting turkeys, chicken, and cut meats. Even though it never performed well as a whole hog cooke, I ended up making a lot of money with the grate configuration.
While my experience was with conventional rotisserie roaster designs, the basic lessons would also apply to a reverse flow. I seriously doubt the horizontal configuration would provide enough space to properly install the rf plate and still have room above the grate for a full sized hog. I also am skeptical the wide, shallow cc would allow for the airflow necessary to prevent hotspots across the grate.
Going with a vertical design provides real estate necessary to get you around most of the clearance and airflow issues, but it does limit total size of the cooking grate.
Good luck, keep us updated.

 

[maineman]

Thanks much! I just found a supplier of 30” dia 1/4” walled steel pipe. Im Now thinking about using that both as a cook chamber and building a firebox from it. The price is good but am I on to something or should I stick with vertical oil tank?

 

[kmmamm]

Personally, I would go with the pipe. 1/4” is much easier to weld and far more durable than the thin walled fuel tank. If you could find a used 230-250 gallon lpg tank, you would have the start of a very nice unit. Where are you located?

 

[maineman]

I was just visiting with a guy today about an LP tank. He is going to get back to me about price and availability. I’m in central PA, about halfway between Harrisburg and state college. Thanks for the advice.

 

[kmmamm]

Good luck! I have always had pretty good luck working with the local lpg co-op. They are always bringing tanks back in that have missing data plates or fail hydrostatic testing and have to be scrapped.

 

[maineman]

My biggest fear is cutting the LPG tanks. I know they steam the tanks to inspect them but I still don’t feel comfortable taking a torch or plasma cutter to them...... if I can find someone to make the initial cut I’d be ok after that.

 

[kmmamm]

Understandable, but it really is pretty easy to purge them safely. If your tank is condemned and coming from an LPG supplier, the valves should be removed. If not, they will need to be removed (pipe wrench and cheater pipe are usually all it takes). Then simply fill the upright tank with water until it is overflowing out the valves. The water is heavier and denser than residual lpg vapors and will simply push them out of the tank. Keep in mind even though the gas has been displaced, there will still be residual mercaptan...it will stink to high heaven, but it is not explosive. The mercaptan can be neutralized by adding bleach to the tank as you are filling it with water. (Some guys will also add some dawn dish soap as well). To be safe, after the tank has been filled with water, tip the tank, drain and repeat. Some guys will leave the tank filled when they make the first cut....a messy process at best. Once the tank is cut opened, a quick burn out will remove any remaining mercaptan.
Personally, I purge every used tank before the first cut, regardless. If the tank is 250 gallons or smaller and I am pressed for time, I will occasionally skip the water and simply fill the tank with C02 to displace the lpg and create an environment unable to sustain explosion. However, I don’t recommend inert gas purging for the average backyard builder as there is a real risk of asphyxiation if not done correctly.

 

[maineman]

That sounds like some sound advice. I know the tank supplier has a local welder come in and replace some of the fittings. If the tank price is fair I may see if he will just cut the opening for me. I can then start the building.
My next thought is that a 250 gallon tank is too long. Maybe cut about 3’ out of it and weld the end back on? I could then use the 3’ fire a fire box maybe?
I looked at the 30” 1/4” walled pipe today, it’s more massive than I pictured. About 100lbs a foot. That seems like a lot of overkill but I’m not sure a LPG tank would weigh much less. The pipe would then require ends cut out and welded on so a tank might be a bit easier in the end? I need to just pick one and go with it, thanks for any and all advice!

 

[kmmamm]

Personally, I wouldn’t cut the 250 gallon tank down. 230-250 tanks are right in a sweet spot where there is enough real estate to do the occasional serious cook, but not so big they take a small forest to heat if you only want to do a few ribs and brats for dinner. Yes, .25“ wall pipe is heavy, but it will match well with the thick walls of the tank. The finished cooker and firebox will be north of 1500 lbs, something to keep in mind as you consider how you will handle the project further down the build. Good luck.

 

[maineman]

I finally made a decision. Picked up a 230 gallon lpg tank yesterday. I couldn’t get past thinking the 30” diameter is much better than the 24” 120 gallon. This thing appears to have been sitting empty without fittings in it a while. I can’t even smell any additive it. Next is figuring out firebox. I’m thinking a 30” dia by 36” long piece of 1/4” walled pipe if I can find a cheap steel wood stove big enough. Any thoughts about either?

 

[kmmamm]

You will be very happy with your choice. If you haven’t already, plug the tank dimensions into a calculator (Dave has one posted up in the sticky’s) to determine firebox, and other critical dimensions.
I would recommend building the firebox rather than trying to adapt an old stove. Better to make it right the first time than spending a lot of time chasing issues trying to make something ”work”.

 

[maineman]

Are there any opinions about a round firebox or a square one? I can get a very reasonable price on a piece of 30” 1/4” thick pipe.

 

[maineman]

First cut made to start building FB. Quick question, is there a certain area that should be under the reverse flow plate? I know the end gap of the plate must be at least as big as the throat between the FB and CC. It seems like the area under the reverse flow plate is dictated by the FB to CC opening size. Am I on track?