The Texas BBQ Forum

Hi all. So I have a smoker that I have had for years. The more I look at it the more I think it's supposed to be a reverse flow. The box is 36x26x20 inches. The chamber is 23x52 inches. There's a pipe (about 8 inches in diameter) that runs from the firebox to the opposite end. But my problem is - the stack is right by the pipe opening. So I want to move the stack to the firebox side. But with the calculator the round pipe will be really long. So I am wondering about making a square stack. But don't know size or length.

What is your Cook Chamber size, and I will help you ' We did a square stack on the last smoker build

This should help;
http://www.feldoncentral.com/bbqcalculator.html

A 6" ID round exhaust would need to be 33" long.

A 6" ID square exhaust would need to be 26" tall.

Sorry I missed your dimensions, My Bad a 4 x 4 sq. tubing would need to be 28 1/5 inches a 5 x 5 would need to be 18 1/4 inches a 6 x 6 needs to be 12. 6 inches

I would probably go with the 4 x 4 or 5 x 5 just for aesthetics The stack Volume is 453.5 ci. in

Gary

Here are a couple of pics

garyspriggs wrote:Sorry I missed your dimensions, My Bad a 4 x 4 sq. tubing would need to be 28 1/5 inches a 5 x 5 would need to be 18 1/4 inches a 6 x 6 needs to be 12. 6 inches

I would probably go with the 4 x 4 or 5 x 5 just for aesthetics The stack Volume is 453.5 ci. in

Gary

Just curious garyspriggs.
How did you figure the volume at 453.5Cu. in.?
If you use the 1/3 rule for the pit calculator the cooker would need 936. Cu. in. of exhaust according to the cookers dimensions.
Link to BBQ Pit Calculator

Sure , no problem. For Years everyone has used Feldon's Pit Calculator, There are some problems with it when calculating for a Reverse Flow

One problem is Smoke Stake should never be calculated on Fire Box Size EVERYTHING is calculated off Cook Chamber Volume

After quite a few RF builds and conversations with other RF builders if you use .020 or even up to .022 this works much better

Also I agree somewhat with the 1/3 rule for the Fire Box. 1/3 is the Minimum you can go larger with no problem and often
better results

But remember EVERYTHING is based OFF OF COOK CHAMBER VOLUME


Gary

garyspriggs wrote:Sure , no problem. For Years everyone has used Feldon's Pit Calculator, There are some problems with it when calculating for a Reverse Flow

One problem is Smoke Stake should never be calculated on Fire Box Size EVERYTHING is calculated off Cook Chamber Volume

After quite a few RF builds and conversations with other RF builders if you use .020 or even up to .022 this works much better

Also I agree somewhat with the 1/3 rule for the Fire Box. 1/3 is the Minimum you can go larger with no problem and often
better results

But remember EVERYTHING is based OFF OF COOK CHAMBER VOLUME


Gary

A lot of the information on the calculator is based on my knowledge of cooker builds I kinda helped design it years ago. My email is attached to it for folks that have questions. Morgan did not design the calculator, he merely made it web based so others could use it. The original which I still use is in Excel.
I have never had a problem with the calculator building a reverse flow cooker. Every cooker I have built and helped folks build work flawlessly. What do you see as a problem on the calculator?

OK fair enough, Why should the smoke stack size be based on FB size


Gary

According to Feldon's a 4" stack should be about 6ft long to me that wouldn't look right at all and a 6 " stack almost 3 ft.

I'm not trying to cause a problem, I'm just stating what we do and a lot of research. And I sure don't want to step on any ones toes.


Gary

garyspriggs wrote:According to Feldon's a 4" stack should be about 6ft long to me that wouldn't look right at all and a 6 " stack almost 3 ft.

I'm not trying to cause a problem, I'm just stating what we do and a lot of research. And I sure don't want to step on any ones toes.


Gary

I agree on the 4" exhaust on looks and function. This is when common sense comes into play and you increase the ID of the exhaust to compensate. A cooker has to breathe and I would never put a 4" exhaust on a 23" x 52" chamber in my opinion it simply is not large enough.
No problems here but I can tell you the calculator if used properly works but it is just a tool like any other that helps get the job done.
When my Good Friend Paul Shirley of Shirley Fabrication was breaking out into the cooker business I helped him design his cookers. They are all based off the pit calculator and still are today. They sell reverse flow cookers Nation wide with about a 6 month back log on builds.
The calculator must be working for some.
I am sure we will agree to disagree on this it makes good conversation.

Cool, Are you Tom ? at the bottom of Feldon's it give credit to Tom ? Here is what it says

Again I apologize if I stepped on your toes, I started out using that calculator and then started making changes

This calculator is based upon the BBQ pit building ratios and formulas developed by Alien BBQ in his revelatory BBQ pit building guides. One of his best articles is Lessons Learned in Pit Building / Modifying. My starting point for this calculator was the Excel worksheet created by Tom C on TheSmokeRing.com (an excellent BBQ discussion forum and website).


Gary

garyspriggs wrote:Cool, Are you Tom ? at the bottom of Feldon's it give credit to Tom ? Here is what it says

Again I apologize if I stepped on your toes, I started out using that calculator and then started making changes

This calculator is based upon the BBQ pit building ratios and formulas developed by Alien BBQ in his revelatory BBQ pit building guides. One of his best articles is Lessons Learned in Pit Building / Modifying. My starting point for this calculator was the Excel worksheet created by Tom C on TheSmokeRing.com (an excellent BBQ discussion forum and website).


Gary

You have not stepped on any ones toes garyspriggs. We are all adults and have opinions I respect everyone's input
No I am not Tom. That would be Tom C we are members of the Smokering.
Alien BBQ is the original designer of the calculator he is a Professor in I believe Thermal combustion. The original version was very basic Tom C with Aliens permission created the Excel Version. Back then (2008) it was limited to folks that could use it so With Tom C's permission Morgan Feldon ( A web designer who likes to cook) created the online version. My part in all this is mostly additions like the half moon opening sizes and what not. Over the years as folks asked questions we tweaked it. Morgan does not build cookers so he asked me if he could tag my email to his calculator to help folks with questions.
I know the calculator works but you also need to know some basics of what not to do like putting a 72" tall 4" exhaust on a cooker. The smoke will cool and stall causing the chamber to fill with stale smoke. We run into these questions all the time that is why I try to adjust the number to what I know will work.
I hope this explains it.

Thanks for the reply, answers a lot. I do understand about a 6' stack, only used that for an example. Me and My #2 son build a pit or two a year. so I'm pretty familiar with sizing
It needs look good ans well as function properly. A long stack cools too rapidly and will not evacuate properly.

I have my own fill in the blank calculator I have used for quite a while Of course it's based on my calculations.

Maybe we could compare notes sometime.




Gary