I'm kicking over potential designs for a reverse-flow smoker and I'd like y'all's input. First, the basics: everything will be made of 3/8" plate, the cook chamber is 55" x 24" OD x 3/8." Any framing (mostly in the firebox) will be 1" square tubing. Why these design choices? Because that's what they had at the scrapyard! Yes, it'll be sturdy enough to survive a war, and heavy enough to anchor a battleship.
Definitely going to be reverse-flow. I think I want an insulated firebox (mostly to limit the temperature of the outside of the box--I have an inquisitive four-year-old). I want to have the option of adding a BBQ Guru (or homebrew equivalent, more likely) later.
With the pipe I have, the interior volume is 23,350 cubic inches. That gives a target firebox volume of 7,784 cubic inches. A firebox with interior dimensions of 20" x 20" x 20" is 8,000 cubic inches, or within 3% of target without requiring precision measuring.
I've modeled a firebox design in SketchUp. Please take a look and let me know what you think of it. I've not built a smoker before, so I'm running strictly on theory here.
The door is 20" x 14," and will be framed with the same 1" square tubing. The firebox-to-cooking-chamber opening measures at 75 square inches (according to SketchUp); the target area, according to the calculator (thank you, Tom!) is 64 square inches, so I think everything is fine there. It's a circular section running all the way to the corners of the box, with a radius of 12" to match the pipe. That makes it about 5 3/8" at its widest point.
The recommended air inlet is 24 square inches; I put two 4" x 3" inlets on each side. Either side alone should give me sufficient airflow, but having a second set on on the opposing side lets me use whichever one is more convenient in the prevailing wind.
The attached pictures show the box framed in with interior skins attached (but no exterior skin). I'll provide the SketchUp file to anyone who'd like it, but I don't have permission on the forum to attach files.