firebox opening vs RF plate not working out

[chaser_2332]

With using all the calcs here im showing i need a firebox opening of 193.55sq". With a radius of 14.625, around 6" up from the bottom put me all over 1/2 of that with the overlapping firebox of the same radius being the same. That being said that puts me at 12" up from the bottom of my cooking chamber, the area calc for my reverse flow plate shows it needs to be around 10" up to hit the correct volume. If i start the plate right at the top of the 12" which is well over the valume at 259.61,that only leaving me 2.625" below the first cooking grate if i wanting it at the center of the cooking chamber. A little insight would be greatly appreciated.

 

[daveomak]

What are the dimensions of your CC ?? and gallons...

 

[chaser_2332]

my cooking chamber has an internal diameter of 29.25" and a length of 72". The pipe im using for the firebox is the same diameter.

 

[daveomak]

48,381 cu in X 0.004 = 193 etc..
1/2 the football shape at 6" high gives 99 sq. in. .... A 12" wide football gives 198 sq. in....
Your RF plate at 12" above the bottom of the CC gives you an area of 260 sq. in... More is better than not enough...
29.25 - 12" = 17.25" between the RF plate and the top of the CC....

You have calculated everything correctly .... The discrepancy arises when you use a round FB over a rectangle... because of the football shape needed for the opening between the FB and CC...

You chose a round FB... that elevates the RF plate... and leaves dead space on the sides, as shown below....
If you can't live with the RF plate at 12" above the bottom of the FB, instead of 10"...
1... Cut off the top of the football....
2... Cut off the top of the FB and weld in a flat cooking surface plate...
3... Build a rectangular FB...
4... Throw out all the numbers and build it to fit your plans...

Blue is "normal" round to round connection.
Purple is Round to Round RF plate location..
Green is square FB to round CC, RF plate location..
Red is a square FB...

 

[chaser_2332]

Thank you, that’s precisely where i am at with it. I think I’ll be better off with a square firebox after running all the numbers. But i wanted a second opinion.

 

[daveomak]

Ahumadora builds some awesome smokers... He has chosen to cut down round FBs and make flat tops out of them to get them lowered... He normally has upper air inlets in the FB... Selling in Argentina, he says some folks can't grasp the concept of the upper air inlet, which he really likes BTW, so to accommodate folks, he deletes the upper air inlet on some home models....