or Connect
SmokingMeatForums.com › Forums › Smoking Supplies & Equipment › Smoker Builds › Reverse Flow › 120 gal smoker build
New Posts  All Forums:Forum Nav:

120 gal smoker build

post #1 of 22
Thread Starter 

Ok folks , i finally found some 120 gallon horizontal propane tanks. So i will be postponing my 250 gal build. I have all the materials. Now i just need tons of technical advice on door dimensions, fire box size, cook chamber cutout, fire box half moon cut out and on and on. I am a welder but i have never attempted a smoker build. Please feel free to advise, comment , criticize as i embark on this build also i beg your indulgence especially when i dont understand things i will ask a million questions on the same topic as i prefer to measure ten times and cut only once. so please if there is anyone who has the time to help i would really appreciate it , i will post pics of what i have accomplishes so far later.

post #2 of 22
Anthony, afternoon...... First we need dimensions of the tank.... length overall, between the welds.... circumference, diameter, wall thickness of the steel and anything else you can provide.... these numbers are important so stuff will fit together properly and the smoker will work as good as good can get.......
post #3 of 22
My Meadowcreek reverse flow is a 120 gallon tank. If you want me to take dimensions off of my firebox smokestack whatever just let me know.

Cooked a rack of ribs on it today just a little over three hours start to finish.
post #4 of 22
Thread Starter 

My friend at the gas company said my tanks have been sitting in their scrap yard for almost 5 years so i stuck my nose in the propane tank fill valve today and inhaled real deeply and there is no propane smell, next im gonna do a flame test with a very long stick and a flaming rag over the valve, seems crazy and risky ,but since  my mother-in-law is out of the country i have to do it myself LOL.  OK Dave please see the tank info you requested below.


The tanks were  made by American Welding & Tank Company and all the info is on a plate welded onto the tank.


Date of manufacture 1999

Weight 260 lbs

Shell thickness 0.140 inches

Volume 38 square feet

Outside diameter 24 inches

Length overall 68 inches

Length between end cap welds 53.5 inches

Circumference  75 inches


For my fire box and baffle plate material i do not have large sheets of steel plate but i have lots of 1/4 inch thick steel plate at 18 x 26 and another set at 18 x 20. they should be just about the right size to make the fire box i hope, please correct me if i am wrong. I almost forgot to say that the build will be mounted on a trailer that is just about 90% finished so i will post pics of that too.


Hey Hdflame any help i can get is appreciated so please go right ahead and hook me up with what you got . Thanks.

post #5 of 22
I'm at the fire station today. I'll try to take some pictures and post some measurements tomorrow after I get home.
post #6 of 22
That tank will work well..... The wall is a little thin BUT..... where you are located.... not a problem....
post #7 of 22
Thread Starter 

Happy to know that it will work.:banana_smiley:.  So this afternoon i decided to play Einstein and play with the circle calculator and it took me 30 mins and one big headache to figure out that i had no idea what the heck i was doing or how the calculator works. Somebody please save me from myself. I will post a sketch to try and explain  what about the cc/fb cutout that is causing me grief and confusion.

post #8 of 22

OK Sly, here are the numbers in the calculator for your smoker. I set the firebox at 100% to get the values for intakes, chimney, and area of the opening. The opening area needs to be 1.5 times what Feldon's requires; therefore, 74 sq-in x 1.5 = 111 sq-in. You need to have about 111 square inches of opening into the cook chamber from the firebox, under the RF plate, and where the RF plate ends at the far end of the cook chamber.


Using the circle calculator, since your radius is 12 inches, and we want an area of ~111 sq-in associated with a given segment height (ED), when I plug in the 12 inches and a segment height of 7, it gives 109 sq-in for the segment area. That's close enough. Now, the chord (AB) is the width of the cut across the tank if you cut at a height of 7" above the bottom of the tank. The chord comes out to be 21.8 inches so the width of your firebox needs to be at least 22 inches so it will cover the width of the hole. Since you have the 1/4" plates for the firebox and you have some that are 26" the firebox can be that wide, or cut three inch strips off and weld them back somewhere else. I've had to cut some strips off for my project and weld them in to make the firebox fit so it isn't that bad.




Hope this helps and keep us posted!

Edited by LenDecaturAL - 8/11/14 at 6:53pm
post #9 of 22
Thread Starter 

Much appreciated Len. I am now in a much better position to start making confident cuts in the tank. I love this site, you guys are genuinely friendly and always will to jump in and help. It amazes me how much knowledge and experience is contained here. :77:

Edited by Sly Anthony - 8/12/14 at 3:15am
post #10 of 22
Thread Starter 

Here are some pics of the main components of the build. Can someone please  tell me what size the CC doors should be on a 120 gal smoker ? also how many racks and spacing and height above the Baffle plate ?  Thanks in advance.




I plan to covert these old aluminum traffic light control cabinets into  warming boxes. I gave the light company manager a suckling pig in exchange for two of them, good deal i think.




This is a 250 gal tank for a future project, a guy at the gas company says i can have as many of these as i like in exchange for a couple of pigs , I cant believe my luck, im gonna raid their scrap yard next week there are all kinds of sizes from 100 gal to 1000 gal tanks all waiting to be scrapped.



My trailer for the project almost finished.



Got two 120 gal tanks to start with

post #11 of 22

Usually, most guys mount the lower grate about 4-6" above the RF plate. If you look on the forum, most of the smokers have the upper grate high enough to clear a butt. Since you have your RF plate mounted at 7" above the bottom of the CC, go up 5 inches and it will put the lower grate at the 3 o'clock position on your tank and then just cut your door somewhere near the top. On the firebox end, don't cut the door over where the firebox is inset since it will be hotter on that end. On the edge is OK since you won't likely have meat hanging off that end. On the end of the RF plate where you left the 111 square inches of opening opposite the firebox, stop before you get to the end of the RF plate since you don't want grease getting into the bottom of the cook chamber. I've seen three racks in a smoker your size, but that would only be good for split chickens or ribs. I doubt you have much brisket in your neighborhood so set it up for pig and chicken. The tanks look great! I would have expected more rust!


Here is a three rack smoker but his is 30" diameter so you can see how it gets crowded quickly.


post #12 of 22
Thread Starter 

Eureka !!!!!!!!  after reading Dave's posts on other threads and using the info from Len I figured out how the circle calculator works and is very simple too :yahoo:Thanks Len thanks Dave , I have even worked out the CC/FB cut out for my 250 Gal build, i will post the figures for critiques just to make sure i got it right anyway. I will  be marking out the cuts today for my 120 gal Build .

Edited by Sly Anthony - 8/13/14 at 4:26am
post #13 of 22
 Thanks Len, i will start marking out the cuts today .

 Good luck Sly and keep us posted on your progress!


Yours is a project I may have to visit when you are done, it would be a good excuse to visit a beautiful island! Feel free to ask questions along the way, we are here to help, it's easier to ask before you go too far down the wrong path.... 



post #14 of 22
Thread Starter 

Sounds like a plan Len You can visit anytime.  Just to make sure i am doing this right i worked out the cut out for my 250 gal build take a look at these figures and tell me i am doing it right or not


Tank volume 250 gal

Diameter 30 in


firebox at 100% is 156 x 1.5 = 234


Radius 15 in

segment height 11 in

Chord (ab) 28.9 in

Arc (ab) 39 in

Segment area 234.8

post #15 of 22

For somebody that has jumped out of a perfectly good airplane that wasn't on fire.... You have done it perfectly! You are now armed and dangerous....PDT_Armataz_01_37.gif 

post #16 of 22
Thread Starter 

 I decided to make the fire box 20h x 20L x24w. Using those figures the cc/fb cut out is now 76.8 sq in x 1.5 = 115.2 sq in as opposed to 74 sq in x 1.5 = 111 sq in from a smaller fire box as previously calculated by Len. My question is will my previous chord of 21.8 inches and my segment height of  7 in from the smaller firebox have to be changed because i have chosen to make the fire box bigger ?  :confused:

post #17 of 22
Short answer is no. Stick with the opening sizes based on a 100% and then build the fire box as big as you want.

Here's the thread that discusses Feldon's in detail and the way it is set up, you will have a better understanding of the calculator and be able to apply it to any of the tanks you take on as a project.

Edited by LenDecaturAL - 8/13/14 at 2:27pm
post #18 of 22
Thread Starter 
Curious question..  do l have to factor in the thickness of the tank wall when making measurements for the CC/FB cutout ?
post #19 of 22
You could, it would add 1/2 inch to the height, but double check the circle calculator to make sure your firebox is still wider than the chord. With 1/4 thk material, it is less than 10 sq-in and shouldn't matter.
post #20 of 22
Thread Starter 

Are redirecting vanes a must ? and if so are there specific measurements for their length and width ?

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Reverse Flow
SmokingMeatForums.com › Forums › Smoking Supplies & Equipment › Smoker Builds › Reverse Flow › 120 gal smoker build