Newbie with a New offset build, need some help

[Texasbdog]

Hi guys, this is my first post other than the wanted section. Looking forward to leaning from you guys.
I'm building a new smoker, rather having it built, and I want to check my calculations if someone could direct me in the right direction. I've researched until I'm not comfortable with the calculations and don't want to blow this build.
The pipe is 22" in diameter and 48" long. I'm going to have a 40" smoking chamber and an 18x18x18" square firebox.
I looked up the Feldon calculations and have come up with a 23.25" 4" stack, 46.66 sq" firebox opening, and a17.5 sq " intake.
I'm planning on having the stack begin at grate level, so does that calculation hold true?
Also I want to install a baffle and tuning plates, would a 12" long baffle run to 5" from the bottom be right and tuning plates at 5" as well or is there a better way to do it?
I'm adding 2 -1/2" threaded ports on the lid at grate level for thermometers, I do use digitals though, adding an expanded metal shelf on the bottom and a drain hole as well as a slide out grate in the smoking chamber. I have a charcoal basket and will add a grate for the firebox. Would 4-5" be enough room under the FB grate?

Anything I'm missing? Thanks in advance for any help!
Texasbdog

[Wtxsmoker]

Welcome aboard. Your calculations seem in line to me and Feldon calc's. The tuning plates should help with even temps as well. I bet it will work well for you. I build a larger trailer pit and used the Feldon site for the size. You can put the exhaust at grate level or on the top there is not a real big difference just read these forms there is a lot of info here.
Best of luck

[k.a.m.]

Welcome to the forum Texasbdog.
Your firebox is slightly larger than needed I like that.
I'm planning on having the stack begin at grate level, so does that calculation hold true?
Exhaust height is measured top to bottom regardless of placement.
Also I want to install a baffle and tuning plates, would a 12" long baffle run to 5" from the bottom be right and tuning plates at 5" as well or is there a better way to do it?
4.5" to 6" distance from the top of your cooking grate and your plates is fine, I prefer 6" but the lesser measurements work as well. I would decrease the fixed baffle to 6" wide and no more than a 25° angle on it.
Would 4-5" be enough room under the FB grate?
Your 4" to 5" clearance on the charcoal grate is fine.
I hope this helps.