Im new to the forum and have done my roll call and I am getting my plans together to build a stump gravity feed clone (Vertical). I understand the operation and all but I was wondering if there was a certain formula or standard that you go by to determine the size of the chute, firebox area, intake opening toward the cc area and ash pan size? I ask because all I could find was Feldon's BBq pit calculator and I know that is for offset smokers and the fire chamber is much smaller on the gravity fed system. Any knowledge is much appreciated.
Gravity Feed Firebox/Chute Sizing?
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Ok, so Ive done some research and figuring and this is what I came up with. The cooking chamber is going to be 23" deep 24" tall and 32"wide. To have the ability to heat this insulated chamber to my max set temperature of 400 degrees it will take about 41000 btu. Since charcoal has a btu rating of 9700 per pound and lump coal has 13000 per pound I will need 4lbs of charcoal burning or 3 lbs of lump coal burning. I am going to design the fire area in the chute to burn around 4 lbs of charcoal and the whole chute to handle 16 lbs total.
I am by no means a mathmetician or into thermal dynamics but from what I have found i beleive this will give me what I want. Hope this helps anyone out there. Ive sort of came up with a formula for different size cooking chambers if anyone wants to try it, and by the way this has not been tested yet. I may be going overboard but I like for my stuff to be right. I will give the dimensions of the fire area when im done designing my chute. If anyone sees something wrong or it does not sound right please correct me on this.
The fire will not burn up the chute because it is sealed so that it is "airtight" and oxygen cannot reach up the chute to burn the coal. The chute is nothing more than a hopper, the placement of the opening from the fire area at the bottom of the chute into the cooking chamber determines how high the coals will burn usually an inch or two above that opening is where it will not have enough oxygen to stay lit. Hope this helps. I am optimistic about what i figured , i guess the only way to know is to just build it which i plan on doing. Thanks for the reply DaveOmak