120 gallon RF build dimension question

[bnew17]

I am planning on starting my 2nd RF build. I built a 250 gal about 5 years ago and really enjoy it.

Our local propane company was scrapping some tanks last year and I have been wanting a smaller cooker to go with my 250, so I decided to pick one up. The tag on the tank says it was built in 1970 and list the dimensions at 24"x67". I'm not sure what that equals to in gallons, but it seems more than 120 , but less than 150 according to the calculator.

I have a sheet of 1/4" plate that is 4ftx8ft I have been saving for this firebox. I was thinking of a 24" square box...which according to the calculator would put me at 136.9%.....would that be ok or too big? I do remember from my readings on here too big is better than too small. I also have some left over 6 3/4" diameter 1/4" pipe I was going to use for a chimney. It tells me 19.33" on that. Doesn't seem like too tall of a chimney to me?

Just wanted to get others opinions before I started. This will be another budget build with recycled materials. I came across some steel roof trusses from a friend of mines shop that was damaged in a recent storm. I have about 120ft of it. They are 2"x2"

 

[weedeater]

The size of the firebox should be fine. Bigger is always better than too small. The 19.33” chimney does sound a little short to me. I think I would stretch it out to 24” or so. Easy to cut off extra later if needed.
Post lots of pics, plan ahead, avoid the big mistake. Lots of good help from lots of good folks on this site.

Weedeater

 

[bnew17]

Question,,,,i have started back on this build. My tank is one of the tanks with the “flatter” end caps, instead of the “semi circle” end caps,,,which just means i have less room for my smoke stack. As with my prior build i try to use what supplies i have on hand. I have a 6 3/4” OD pipe that is about 5/16” thick. The pipe is too wide to so a straight vertical exhaust like i would prefer. It looks like i will have to do a 90 deg elbow. Will this work?

 

[daveomak]

Weld a plenum on the end of the tank for the stack to connect to... mobetta for air flow....

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[daveomak]

An exhaust stack of ~36" is necessary to achieve the pressure drop for good air flow in a smoker....

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

Exhaust Calculation..

ESV in cubic inches_________ ... = Stack Length in inches (36" +/-)
0.7854 X Stack Diameter X Stack Diameter

ESV in c.i. = D2 ... Diameter of the stack squared...
0.7854 x 36
10/3/2019 edit


Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
this is for round stacks only..

 

[daveomak]

Tanks have a dead space volume to accommodate expansion....

 

[bnew17]

Ok. I will have to check but I dont believe i have any other pipe. I do have 36” of this pipe. Would it work just to use it and make it 36”?