Very Small (12.3 gallon) propane tank reverse flow

[MeltedSolid]

Hey all, I was wondering if you'd be able to confirm that I'm not crazy with a smoker design I'm thinking of making. Some background, until now I've only done smoking on a Masterbuilt electric chip smoker, and that thing works great, but it's just a little too small to cook a brisket without hanging it from the top grate for the first half of the cook. Also, I go camping occasionally and I want to be able to bring a smoker camping with me, so I'll eventually be attaching this to a tow hitch. Anyways, all of this has led me to want to build a small and portable offset smoker. I came across a free 30 lb propane tank (12.3"x19.5" chamber) and a few 20 lb propane tanks (12.3"x13.5" chamber), and came up with this design:

Link to Feldon's BBQ Pit Calculator

The dimensions in the CAD are measured from the propane tanks I have, so there's some unevenness which will be real. I've got access to a waterjet cutter at work, which is going to make the build a lot easier. I was thinking a reverse flow makes more sense for a smaller smoker because thermal mass will be a concern, so adding as much steel as I can will be helpful. Everything shown in the CAD should weigh about 70lbs. I also was hearing around that for a smaller smoker you want to oversize all of your airways, so my intake pinwheel at max open is 7.2 sqin, ~2x larger than the calculator, and my firebox outlet is 15 sqin, ~1.5x larger than the calculator. The exhaust is using 2" 16 gauge car exhaust pipe. The wall thickness of the propane tanks is 3/32" (0.09375in), and the waterjet parts are 11 gauge (0.1196in). The firebox is insulated around the diameter, with another propane tank cut and pulled out to make the outer wall around the insulation. The firebox is 12" diameter x 10" long, 120% of the calculator.

Let me know what you think, will this be a worthwhile project, or will this be a nightmare and literal trial by fire for learning how to do fire management? Do I need a larger firebox? Anything else I should probably change? I'm not new to fabrication, but I'm totally new to smoker building so any input would be helpful!

 

[civilsmoker]

I would make your stack 3 inches in diameter (and place it near the top of the tank (like my copper pot built in the thread below), not angled out the side like you have it, ie that will cause too many losses) and I would us a 20lb tank in the vertical direction for the fire box ( so yes bigger FB the fire needs volume to breath), this set up will work very good.

Just sharing this build from a long time ago….
https://www.smokingmeatforums.com/threads/first-build-11-gallon-mini-pig-cooker.206867/

Good luck and post build picks as you go

 

[MeltedSolid]

Thanks! I was searching for a while for examples but didn't see your build, that's exactly what I'm looking for!

 

[civilsmoker]

Thanks! I was searching for a while for examples but didn't see your build, that's exactly what I'm looking for!

The suggestions I gave are based on my builds and will make your build work nicely!

 

[MeltedSolid]

I couldn't figure out how to use the 20lb propane tank vertically for the firebox and keep the firebox the way I wanted it, but instead I decided to cut the propane tank along the length and expand it out in an effort to get to the 1.5x of the calculator number. Side bonus is the top of the firebox should be able to be used as a small stove.

 

[MeltedSolid]

Posting an update, I've started assembling the frame and the hitch mount for the smoker and welded the two propane tanks for the cook chamber together. This is a picture of a mock up of it on the car.

Final form will look like this with legs and adjustable hitch mount:

I probably won't get the chance to go camping with it until next year, but that'll give me the winter to dial it in before a trip. I'm getting excited to try it out.