Could use some help here. So I have been working on this build, have gotten up to a point where I am mounting the exhaust stack and I just started looking everything over. I stumbled across SMF (Smoking Meat Forums) and have been reading through the pit builds and there is a guy over there (Dave Omak) that frequently gives advice and links to a "Reverse Flow tutorial often". I've gone through the tutorial and recrunched my number (yes, I know kinda late in the game) but I discovered something that is making me sick to my stomach as I think I may have made a crucial error...
I discovered the tutorial and subsequently the "Circle Calculator" (
http://www.1728.org/circsect.htm). According to the tutorial I calculated merely off of diameter which I thought I was good to go according to Feldons Calculator. But once I used this Circle calculator and calculated for "Segment Area" mine came out to only 63.5"!!! When I am supposed to have 123" according to the Circle calculator (mind you the diameter checks out). My AB Chord is: 18" and my Segment ED is: 5"
HERE ARE MY NUMBERS BASED OFF THE TUTORIAL BELOW:
Calculations for a standard design, reverse flow smoker..
Volume of the Cook Chamber.... Use the Inside Diameter of the tank... All smoker calculations are based on the volume of the Cook Chamber....
Diameter X Diameter X 0.7854 X Length (24x24x.7854) = 30,762 Volume in cubic inches / 231 = (133) Volume in gallons
Volume in cubic inches X 0.004 (30,762x.004)= (123) FB/CC opening in square inches
Volume in cubic inches X 0.004 (30,762x.004)= (123) Area under the RF plate in square inches
Volume in cubic inches X 0.004 (30,762x.004)= (123) Area required at the end of the RF plate in square inches
Volume in cubic inches X 0.33 = (10,151) minimum volume of the Fire Box
The above areas are necessary for great air/heat/smoke flow.... using less may cause an overheated FB.... Narrow / Long CC may require an increase in those numbers due to increased surface area friction to volume... Wide/Fat Short CC may use smaller numbers due to reduced surface area friction to volume...
Volume in cubic inches X 0.001 = (30.762) FB air inlets in square inches...
Recommended upper and lower air inlets... Upper air inlet directly across from the FB/CC opening to facilitate moving heat from the FB to the CC, and insuring good air flow through the CC.. The lower air inlet should be situated at or below the fuel grate.... The two air inlets can share the designated square inches of opening.... approx. 20% upper and 80% lower...
Volume in cubic inches X 0.022= (676.76) 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..
.7854x6x6 = (28.27") Stack Length in inches (36" +/-)
0.7854 X Stack Diameter X Stack Diameter
So, in short, I feel like I really really screwed the pooch on this one and didn't make my FB/CC opening big enough. I'm hoping/crossing my fingers that where I am at right now is going to be ok, but I'm just not sure now. And like I said, I have an insulated FB, it's fully welded to the tank, I've started to mount up the exhaust stack and was going to move onto the RF plate next UNTIL I stumbled across this. This is just going to be a nightmare to tear apart if I have too...just lost atm and could use some guidance.
Any help/assistance would be certainly warranted.
Thanks guys.
Dale
ray:
