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

[MikeFromTexas]

Finished my reverse flow build about 1 month ago. Not wanting to reveal my nerdy innards by performing a flow analysis through engineering software, I decided to follow the recommendations in this thread/tutorial. All I can say is that my pit is a great flowin machine. Great temperature control, temperature distribution and doesn’t seem to use that much fuel (about 12” log per hour).

specs:
45” cookin chamber
18” OD x 1/4 wall.

i’ll say this though, I spent a lot more money than I thought I would. Kinda like when I build ARs..

 

[daveomak]

Mike From Texas, thanks for the revue of our tutorial... Most folks have found the same...

 

[Trus]

Hello Im new to the site and getting ready to build my first smoker. Been smoking on a few types of smokers at academy and such. Anyways, I am looking to build a squared CC Reverse Flow. I started to calculate the dimensions as stated in the thread but im not sure if im doing it correctly. Here is what i have. Please correct me if im wrong.

Cooking Chamber: H= 36" (3ft) W=42" (3.5ft) L=30" (2.5ft)
Ive looked up the conversion for a square box to gallons and this what I have.
cu ft = (3ft) (3.5ft) (2.5ft) = 26.25cu ft
gal = cu ft * 7.48 = 26.25cu ft * 7.48 = 196.35 gal

Volume in cu in = Gallons * 231 = 196.35gal * 231 = 45,3656.9 cu in

Volume of CC (Used Inner Diameter)
H=35 1/2" (2.95833ft) W= 41 1/2" (3.45833ft) L= 29 1/2" (2.45833ft)
Volume of CC in cu in = (35.5)(41.5)(29.5)(0.7854) = 34134.2 cu in
FB/CC Opening in sq in = Volume in cu in * 0.004 = 34134.2 cu in * .004 = 136.537sq in
Area under RF Plate sq in = 136.537 sq in
Area required at the end of the RF Plate = 136.537 sq in
FB Volume Minimum = Volume in cu in * 0.33 = 34134.2 cu in *0.33 = 11264.3 cu in
FB Air Inlet = Volume in cu in * 0.001 = 34134.2 * 0.001 = 34.1342 sq in
Exhaust Stack Volume (ESV) = 34134.2 * 0.022 = 750.952cu in
Stack Length = ESV / 0.7854 (Stack Diameter)(Stack Diameter)
Stack Length = 750.952cu in / 0.7854(6)(6) = 26.5594

Okay im done, Im not sure if the calculations are correct please help me out. THank you

 

[daveomak]

Refigure the numbers using length of the cylinder, diameter of the cylinder... That's all you need...

Height, width, length are confusing and there are only 2 dimensions to a tank...

 

[Trus]

Refigure the numbers using length of the cylinder, diameter of the cylinder... That's all you need...

Height, width, length are confusing and there are only 2 dimensions to a tank...

Thanks for the reply,, if the depth of the cc is 30 in, would that be my diameter?

 

[daveomak]

Look up diameter, length etc...

 

[Blwaz23]

Wanting to build a reverse flow smoker for the first time. CC is going to be 24" in diameter and 40" in length. The FB is going to be 20" diameter and 20" length. Both are going to be made out of .250" steel. Using the calculations from the first page this is what I came up with

Volume of the Cook Chamber.... Use the Inside Diameter of the tank...
23.5" X 23.5" X 0.7854 X 40" = 17,350 cubic inches
17,350 X 0.004 = (69.4) FB/CC opening in square inches
17,350 X 0.004 = (69.4) Area under the RF plate in square inches
17,350 X 0.004 = (69.4) Area required at the end of the RF plate in square inches
17,350 X 0.33 =(5,725) minimum volume of the Fire Box

Using that minimum volume of the fire box I based my firebox measurements off it and came up with a firebox 20" long and 20" diameter (5,972 cubic inches) its slightly over the minimum. Should I go slightly bigger or that is slightly oversized enough?

Can someone double check my math on the CC/FB opening? I came up with an opening that is 6.5" tall and 15.5" wide. Brain had a tough time understanding that calculator fully. Using the height of this opening the baffle will go slightly above the opening for the air to flow? Also how high should the cooking rack sit above the baffle? I'm thinking 5" above, and advice from experience is appreciated.

What kinda pipe would ya'll recommend for the stack and the length? Does the plenum sit at cooking grate level or and inch or two above it and should it be as wide as the cooking grate? I'm sure all of these questions has been asked and answered before but I just wanna make sure I'm doing it the right way.

 

[dacolson]

PM sent.

 

[rez667]

Evening folks...... Please try this calculator out to help find errors..... This thing was a PITA to put together.... cut and paste... and other stuff I don't know about...
DO NOT COPY until we have all the errors straightened away..... then have at it...


HAVE AT IT !!!!! any problems... I'm here.....

I know this is a super old thread, but is this calculator still around? My head is starting to hurt from doing all the math :-(

 

[dacolson]

I made a spreadsheet for it. It's not perfect but if you don't mind messing around a bit it does all the math for you.

 

[rez667]

I made a spreadsheet for it. It's not perfect but if you don't mind messing around a bit it does all the math for you.

Thank you. I will give it a shot

 

[daveomak]

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

 

[rez667]

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

I think I misunderstood the post. I saw the the circle calculator spreadsheet , I thought there was one for the firebox etc. Than kyou for the reply though! Also, thank you for all the quality posts. I am learning a lot from this site

 

[dacolson]

I think I misunderstood the post. I saw the the circle calculator spreadsheet , I thought there was one for the firebox etc. Than kyou for the reply though! Also, thank you for all the quality posts. I am learning a lot from this site

I will PM you.

 

[physicthing]

hello all,
Not a smoker myself, but amateur welder with best friend wanting smoker. Been reading and following forums here for a bit and find alot of folks really like the reverse flow. I have calculated most of the different parts but have a few dimensions that I am not seeing. height and size of door?
height of meat racks? and what height does the exhaust stack leaving cc. I am dealing with .25 plate rolled into 48"x 30.55" diameter cc. or should be that is what a 4'x8' should roll to. I know alot of guys use ac tanks and propane. But I'm a commercial electrician and have a fabshop that will roll my cc chamber as a favor. I just had to by the sheet.

any discussion help is mucho appreciated.

 

[daveomak]

 

[slidinstar]

I've skimmed over the thread, and I don't believe this has been discussed as it relates to the calculations....
If I have a vertical box at the end of my horizontal with an additional stack/exhaust, does this add to the volume of the exhaust?

 

[daveomak]

I don't think so.... What the calculator tries to do is get a great flow and even temps in the primary cooking chamber... Anything "down stream" is using the waste heat and CC air flow.....
As long as you do not try and adjust temps, of the vertical chamber, using the primary temp controls..
The inlets should be used to adjust the temps in the CC... AND do not adjust those 2 stack caps to adjust the CC temps..

 

[MiNi]

Hello all and greetings from Finland.
I´m new here and recently started to think about building a smoker myself, and these instructions here has given me a lot, thank you for those.
I have one question regarding the RF plate. I designed an RF plate with perforated holes (attached photo) in it and did some flow simulations for it. Based on those simulations, the smoke in the chamber looks more evenly distributed than in the RF plate where the opening is only on the other end of the plate. Are there some drawbacks or something to consider in a plate like this? Thanks.

 

[daveomak]

If you don't like it, you can always throw a non perforated plate on it and go with the original design....