Question about cc and fb opening

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agonolin

Newbie
Original poster
Jul 19, 2017
25
15
New York
So I'm in the planning phase of my first build. I like to have a step by step plan for everything before I start or I will always miss something. I've been using Feldons calculator because I'm not making a reverse flow. I have an 85 gallon tank and plan on making the fb 20"x20"x20". According to the calculator the fb is plenty big for the cc so I'm not to worried about that. The calculator also said that the half moon opening should be 12.77 inches in diameter which I can do.
My question is, if I use the full 20 inches from the width of the fb as the diameter for the half moon will that be to big? Is there such a thing as having to big of an opening? I just think it would look silly to have the corners of the fb sticking out 3.5 inches out on each side. Any input would be greatly appreciated thanks!
 
Last edited:
Post some pics. You have a 20x20 firebox and a 85 gallon tank which you don't give the diameter of. Then you say the firebox will be sticking out each side 3.5 " ? Am I missing something? So you have a 13" diameter cook chamber?
 
Sorry about the confusion. The diameter of the tank is 24 inches. I drew up a quick sketch to try and get my point across. I apologise about it, I'm rushing and the paper is all I have in arms reach because I'm trying to respond to this before I go to sleep. Hope this helps. IMG_20171010_214037.jpg IMG_20171010_214011.jpg
 
Your numbers sound off to me. I just built a cooker with a 24" dia tank and a 24" square FB it stuck out from the CC a half inch each side at most. Also you said the opening should be 12.77 diameter. But your planning a half moon cutout. Where did you get these numbers? Your FB should end up smaller than the diameter of the tank by quite a bit beings it's already smaller. Check your numbers again.

Kyle
 
It will not look silly in my opinion there are plenty of cookers that the firebox extends past the cooking chamber. I would increase the 12.77 to 13.25" wide x 6"-5 1/8" tall. This will allow for a 1.5" grease bridge at the bottom of the opening.
 
I have been using Feldons calculator. Here is the link to what I have input.

Link to BBQ Pit Calculator

Thanks Kam for your response and I will definitely take that into consideration but I am still curious as to if using the full 20 inches will be detrimental to the cooker? Thanks for your help everybody!
 
You could change your firebox dimensions to be taller and narrower. That way it wouldn't stick out. Also your tank looks like a water pressure tank. It probably has a rubber bladder inside and it's probably pretty thin walled.

Kyle
 
It is a water pressure tank but it's doesn't have a bladder. It has an epoxy coating that I figured I could burn out after I cut the door. I'm not sure of the thickness yet because I haven't cut it open but I bought it from a guy for 10 bucks so I thought I would give it a try. If it's too thin I'll just take it to the scrap yard and try and find a new tank that's thicker.
 
That coating is really hard to get off and will offgas the first time you get it hot enough. Cut it outside. I built a vertical smoker from a tank that had that liner, it makes nasty fumes but only once. Your welder also will not ground through that stuff so you have to grind it off anywhere you plan on welding.

Kyle
 
I have been using Feldons calculator. Here is the link to what I have input.

Link to BBQ Pit Calculator

Thanks Kam for your response and I will definitely take that into consideration but I am still curious as to if using the full 20 inches will be detrimental to the cooker? Thanks for your help everybody!
The calculator is based on a 1/3 rule. It calculates everything needed to build a cooker that works now changing openings and what not will most likely work once you figure the cooker out but I have never found the need to test the water.
Some things to consider is your small cooking chamber. With a huge hole the firebox end will be toasty from all that heat flowing in not to mention intake air will need to be at a premium to create a draft. Keeping left and right remotely close is going to be a challenge. These are things I would think about.
I hope it helps. :)
 
That coating is really hard to get off and will offgas the first time you get it hot enough. Cut it outside. I built a vertical smoker from a tank that had that liner, it makes nasty fumes but only once. Your welder also will not ground through that stuff so you have to grind it off anywhere you plan on welding.

Kyle

Ok thanks for the tips about the fumes and the coating. I'll make sure to grind it before welding!

The calculator is based on a 1/3 rule. It calculates everything needed to build a cooker that works now changing openings and what not will most likely work once you figure the cooker out but I have never found the need to test the water.
Some things to consider is your small cooking chamber. With a huge hole the firebox end will be toasty from all that heat flowing in not to mention intake air will need to be at a premium to create a draft. Keeping left and right remotely close is going to be a challenge. These are things I would think about.
I hope it helps. :)

Sorry Kam I don't think I understand what you mean about keeping left and right?
 
Ok thanks for the tips about the fumes and the coating. I'll make sure to grind it before welding!



Sorry Kam I don't think I understand what you mean about keeping left and right?
Temperatures on the left side of the cooking chamber right side of the cooking chamber.
 
Oh duh that makes sense. Maybe I'll run the numbers changing the height and width and see what I come up with. Thanks again everyone for the help. I'll post some updated numbers later tonight
 
Link to BBQ Pit Calculator

This is all the updated information. What do you guys think? Will it proportionally look ok or do you think it will look silly? I was thinking I would attach the whole 15 inches and just put an inch or two grease bridge. Should it work ok? Thanks guys, I've been digging in old posts all evening trying to learn all I can. Thanks for all the tips!
 
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