Hello Hoosier_j and welcome aboard!
So your tank being oval - or oblong - makes these calculations a little more challenging but still not to complicated. So first off, it's important to calculate the volume of your cook chamber tank. All other calculations can be made from that number. Using the dimensions you gave above, I calculate the volume of your tank to be about 238 gallons. Is that what you get?
Next, a good practice is to run your numbers through a pit calculator - there are several good ones online. Here's the one I like to use:
The SmokerBuilder® Official BBQ Pit Calculator will help you design and build your smoker according SmokerBuilder's proven design calculations. Ensure that your smoker is sized appropriately and save time and money on your build.
www.bbqpitcalculator.com
Using 238 gallons for the CC tank, the calculator says your fire box should have a volume of 18,326 cubic inches. The dimensions you gave above put the actual volume of your FB at about 118% of that target...which might be a little too big. If possible, you might think about reducing the size of the FB until your actual number is between 100 and 110% of the recommended volume. A professional pitbuilder whose advice I trust told me that's the "sweet spot" for FB to CC volume ratios.
Then next is the stack/chimney. Are you planning a round or a square stack? The calculator says that if you went with a 6" round stack, it should be 38" tall. The calculator won't advise you on where to place it. My best advice would be to locate the opening from CC to the stack at or just above the level of your upper cooking rack. I built a RF smoker last year. Here's a couple pics that show where I placed that opening on mine. My CC was round instead of oval, but you can still get an idea of where to place yours.
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I you want to browse through it, the link to that build is here:
Howdy SMF Brothers and Sisters! I started a RF patio smoker build several months ago...and kept meaning to start a build thread here. So I'm finally getting around to doing that! I started with this propane tank. It's 5/16" thick, and 24" diameter by almost 11 feet long. I plasma-cut the...
www.smokingmeatforums.com
Your throat opening - the FB/CC opening - can be calculated too. According to all the other numbers, the area of your throat opening should be about 173 sq. inches.
The only other important number to calculate is the area of your intake vent on the FB. That calculator says yours should be about 65 sq. inches.
I hope any of that helps, and I apologize if I'm sharing information you already know. One of the first and most important things to do when designing a new build is to get those dimensional numbers close. It's the best way to be sure your new smoker will draw properly. Air flow is the key to a pit that performs as it should.
Good luck with the build! I'm looking forward to following!
Red
