54 gallon reverse flow

[grant finn]

Hi,
I'm in NZ building a smoker out of an old pressure tank that measures 21.25" id by 35". I followed the calculator as best I could and just want to double check my dimensions before building the firebox. The calculator asked for a box 15x15x20?
Also an opening of 36 inches?
I noticed later on in the calculator post that he reccomends enlarging the opening by 50% on a reverse flow smoker?
Just a little confused as we work in mm and CM rather than inches etc but starting to get my head around it.
Thanks for any help

 

[daveomak]

The 50% enlarged opening is an aside... I was speaking of Aliens build tutorial.. (Feldon's calculator) and the problems it had.... and how we fixed the original problems... Follow the numbers in my tutorial and you will be golden.....

Smoker Calculator reasoning
The concept for the changes is below.... Alien and his associates, did an amazing job putting the original calculator together... 100% of my numbers are based on his original numbers... small changes were made for the improvements due to design changes in smokers.....
The original measurements were taken from SFB smokers with tuning plates I do believe.... The advent of the RF smoker did not make any changes to the calculator... Now the exhaust has to travel twice as far as before, and the original FB/CC opening restricted the air flow from the FB, causing the FB to over heat... Some would get up to 450 deg and higher while the CC wouldn't get over 250.... And then there is the increased friction from the steel.... When using natural draft, any restriction/friction is very detrimental to the flow....
So, on a whim, the FB/CC opening was enlarged, the area under the RF plate was increased and the area at the end of the RF plate was increased... all by 50%.... That solved ALL the problems.... fuel consumption was reduced.... folks were happy....

 

[grant finn]

Thanks. I've got all the numbers from your calculator written down and ready to go. I'll try load a few photos of the build as I go

 

[grant finn]

OK hopefully someone can just double check my numbers for me before I start getting too far ahead.

CC is 54.35 gallons, 12554.8 in3

FB should be 4143 in3, 14x15x20

FB/CC opening 50 in3 ?

Inlet 12.55 in3, 1" x 2" 7 of, 3 high and four low.

Stack 4" x 22" ?

Most of the numbers I'm sure I've done right except maybe the FB/CC size? Another calculator said 33.6 inches for the opening. Just a little concerned as 50 inches seems big?

 

[daveomak]

FB/CC opening is actually 50 sq. in. .. I took liberties with the math to reflect the actual opening...

Those are the numbers I would use... because of the smaller smoker...

125544 x .022 = 276 / 0.7854 x 16 = 22" tall...(4" stack) I would change that to 30" due to the size of the smoker... Just one of those things with a smaller smoker......

 

[grant finn]

Thank you for your help. I really appreciate it, we don't have the big sized tanks over here that a lot of people make smokers out of. It was a struggle to find something that would work

 

[daveomak]

Your FB/CC opening is the green area... Follow the circumference of the CC... Measure up 5 1/4" or so... draw a line horizontal and cut... Slide the FB up to the cut out... mark the FB from the inside of the CC.. cut the opening out of the FB.. You can slide the FB into the CC as far as you like... Weld the RF plate to the top of the FB... It will be easy to measure what's needed for the RF plate once you have it welded into the CC... I would leave at least 5" at the end of the RF plate for air flow... Leave about 4-6" above the RF plate for the food rack.. A dam on the end of the RF plate is a good idea.. install a drain that goes through CC to the outside for grease to run out, if needed... You don't want a grease fire.. You may also want a drain on the CC to was it out... Leave a 1" lip on the bottom of the cutout for the FB.. that will be a dam to stop stuff from running into the FB.. Grease mainly... The upper and lower air inlets are awesome for fire control.. They take some getting acclimated to using them but they are worth it...
..

 

[grant finn]

Thanks for all the helpful information. I'm building the firebox at the moment and hope to have it completed today

 

[grant finn]

Smoker all finished. Works really well. Thanks for the all the help with the calculations for sizes etc

 

[daveomak]

Grant, morning.....
Food looks beautiful... Nice clean smoke... I'm glad you were successful with your build.... Good looking smoker....

Dave

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