Smoker Calculation question

[benziebbq]

Hi-

This site has a great calculator and calculator discussions. I would think that the CC / FB / Exhaust calculations would be the same whether you were looking at a standard offset or a slightly modified Downdraft style (Jambo-type port into CC). It seems that just raising the FB and lowering the Exhaust would not change the overall calcs.

Do I have that right?

I am very grateful to have found this site.

 

[daveomak]

You want the exhaust stack to be about 36" above the top of the CC..    upper air inlet on the FB is important to move the heat into the CC...   I would use the ....    Volume in cubic inches X 0.022 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV) .. (The increase in volume ~30% shows a dramatic improvement in equalized temperatures across the cooking surface... edit 6/19/15 )

Exhaust Calculation..

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

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..
 

http://www.smokingmeatforums.com/a/reverse-flow-smoker-how-to-calculate-build-tutorial

... Drawing is not to scale........                                                         ... I would use a plenum for improved exhaust flow....

Jambo Design.jpg

• daveomak
• Mar 14, 2017

 ....

Stackideas.jpg

• daveomak
• Mar 14, 2017

 

[benziebbq]

Good info on the stack, Dave. Thanks for that.

Mine won't be RF. Just a standard horizontal offset, but with downdraft porting. Like this thread: http://www.smokingmeatforums.com/t/142517/three-some

I like the bigger round stack idea. Thanks again.

I'm looking at a24" 1/4" pipe, rather than the 20" 1/2" pipe in that build thread. Either 48" or 60" long.

 

[benziebbq]

Dave-

When you refer to a plenum in your groovy pic, you're referring to the angled "scoop-like" aspect of it?

 

[daveomak]

Yep..

 

[benziebbq]

Thank you Dave-

That's really helpful stuff.

 

[daveomak]

And.....   that's why I put this drawing in post #2.....  The numbers are the same...  You could tweak them but....   if it works good for a reverse flow, with more friction than a SFB down draft, what would be the point...

Jambo Design.jpg

• daveomak
• Mar 14, 2017

 

[benziebbq]

No sense tweaking what works

 

[daveomak]

You got it... 

 

[benziebbq]

firebox2Model1.jpg

• benziebbq
• Mar 15, 2017

The calcs are not what I need, since I'm going 24" dia, but the lineup of the vents and stack relative to the grate is what seems good. The vent from the FB to the CC would still have the flair.

Smoker.jpg

• benziebbq
• Mar 15, 2017

The Exhaust:

smokervent1.jpg

• benziebbq
• Mar 15, 2017

So while the vents line up, the flair is tossing the heat up, mixing the air up there, and then downdraft to the stack with damper.