# New smoker build

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<snip>When using the Feldon calculator it tells me I should have 51.75 Square inches of area open for the segment opening with a 5.75 radius (bold mine). </snip> The tank is 20” diameter (bold amine again) and Feldon shows the cook chamber size as 18480 cu in. BBQ calculator.com recommends 57 sq in throat opening. So if I have cut the opening too big can I reduce the opening by adding a grease bridge at the bottom so grease won’t leak back in the firebox ? Any advice would be greatly appreciated
As someone who recently went through this, I am not picking nits here. I want to make sure I'm plugging in the right numbers. I believe where you write "radius", you're referring to Segment Height. Since you mention "20-inch diameter", I used 10" for the radius.

Working your numbers backwards since I think you're asking "Which is correct: 51.75 or 75 sq in?" - and - "How high should the segment I'm removing be?"

Using the formulas in this post :

51.75 would be correct if the inside length of your tank is 41.25"
Segment Height = 4.375" (4-3/8")
Chord = 16.5"
to achieve an area of 50.8 sq in... almost 51" (another 1/8" to 4.5" Height with a slightly longer chord puts you at 52.9 sq in).

75 sq.in. would be correct if the inside length of your tank is closer to 60"
Height = 5.75" (a number you already mentioned so I'm guessing this may be the length of your cylinder.)
Chord = 18" (18.1" if you're better with the cutout than I am.)

If you cut too much all I can say is, "No big deal. You're obviously handy and secure enough in your skillset that you even started this project instead of running out to a BigBox store." So two options immediately come to mind:

1. Weld in a piece of flat along the bell to lower the firebox, or

2. Cut the top of the corresponding smiley-face mouth in the back of the firebox down a little lower to make it smaller.

Which option you choose will be based on your desired outcome:
Do you want the firebox higher off the ground but subsequently closer to the grease plate and cooking grate? - or - (cut the firebox opening to the corrected size)
Do you want the firebox further away from the top? (add the flat to the bell).

If I'm way off-base or coming across as anything other than trying to help a brother out, I apologize in advance.

Regards.

JLeonard
SpottedLantern

I agree with Idea #1 ...

#2 Idea has the potential of creating a flow problem... IMO ... A wide flat across the top (more friction) of the opening in the firebox will create blockage for a smooth (less friction) transition of the heat into the Cook Chamber ...

JLeonard
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