firebox to CC opening for a new build

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Original poster
Apr 21, 2014
  Starting to build a new smoker and want to make sure my figures are we go... the tank is 24" diameter x 83" long...I built a 24"x24"x24" square firebox...I have a 5 1/2" OD pipe for my chimney that says it has to be 27.89" long...I cut 2 openings in the bottom of the side of the firebox closest to the firebox door away from the CC so I have 1 in the front of the firebox and 1 in the back...the holes are 3"x9" for the dampers that I can completely close or open with a sliding door...went bigger than the calculator said just incase I ever needed more air flow...My biggest issue is I can't figure out what size or how to mark my firebox to CC opening...all help would be greatly appreciated from a 1st time pit builder...thx and have a good one
Your FB to CC opening needs to be about 150 sq. in......

Using the link below, click on Radius and Segment Height ED....

Enter 12 for the Radius....... for Segment Height ED, adjust that number (9) until you get close to 150 sq. in. in the box marked "Segment Area" .... Then look at Chord AB... (23.23) is the width of the RF plate

The shape of the cutout will be the circumference of the tank and 9" high from the bottom... Cut into the tank just past the weld ring, if you are using a propane tank, to mount the FB.... Check out Ribwizzads plan for welding those together.... It makes life easy......

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thx for the reply if I get the tank straight with the valves on the bottom for my drain...I then need to measure up 9" from the bottom and cut straight across from side to side for the mouth to weld the firebox into? then weld the firebox up to the tank then cut that same size hole into the firebox or should I leave a 1"lip on the firebox to keep grease from dripping back into the firebox?
should I leave a 1"lip on the firebox to keep grease from dripping back into the firebox?

Good idea on the "grease dam" straight across 1" to 2"... I've also seen additional drains added to the CC for grease and clean out...

I don't know where the link went in post #2.... Links to smoker build have been given Jeff's blessings....
I am late to the party but this is a great post.  This exchange has been extremely helpful as I have been trying to figure this out.  I read this post and the light came on immediately.   It really is a simple solution to a very complex problem.   The lip is important as well.  Now if I can figure out how to make an easy job of installing a baffle. I think this is just going to be a lot of cutting and welding.  Thanks for these great idea.  Go low and slow. is reader supported and as an Amazon Associate, we may earn commissions from qualifying purchases.

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