How do you (personally) figure firebox size?

[DocMorgan]

So, I am starting to plan to build two smokers. One from a 100# bottle that will "mimic" the volume to a smaller scale of the same type of build that I will make the bigger one with. Hoped you were able to follow that... Cause my head spins reading it. Basically... I'm buildin a smaller one with the same ratios that I want to build the bigger one with. For the sake of dealing with larger numbers, I'm throwing the numbers from the bigger tanks for the bigger  smoker out there.


So to calculate the volume of a cylinder, the formula is V = πr2h
π = 3.14
r = radius (of the cylinder, distance from the center of the cylinder to the outside wall on a plane parallel to the top or bottom of the cylinder) in this case r is squared or (r*r)
h = height

The measurements for my large tanks, minus the larger domed end that will get lopped off, are 95 inches circumference and 32 inches for height not considering the somewhat domed end that remains (in this case the bottom of the tank). A circumference of 95 inches = a radius of 15 inches or 1.25 feet. The height of the tank in the areas where the tank is not "domed" is approximately 32 inches or 2.66 feet. Now, plugging all that into the formula above gives me 13 cubic feet in a tank, 26.1  cubic feet if I put them together, without considering the area in the "domed" end of the tank(s).

Now, if you apply that 1/3 size firebox to the 13 cubic foot volume of the one tank... It would require the firebox to be about 4.3 cubic feet, or better than 8.5 for the two combined. 

Of course you want to figure room in the box for a removable ash pan, perhaps some fire brick to hold heat, etc... And then I am sure you have to account for the domed ends (however shallow) and would you figure a warming box with live smoke into the whole scenario as additional volume?

Anyone want to share how they "figure" the size for their firebox?

- Doc

[Frank_Cox]

for the sake of the firebox size, the 30% rule is a real close number. it can be bigger, not smaller.
for the volume of your cookchamber, the best way to do it is to figure the cylinder part of the tank and add it to the volume of the endbells. now, the endbells are the tricky part... it depends on if they are elliptical or spherical. put the 2 endbells together and figure the volume of them and then add the 2 figures together.

[The Czar]

...... ... ......are we talking about?

[GreenSmoker]

http://www.feldoncentral.com/bbqcalculator.html

Easier for most of us.

[DocMorgan]

Thanks GS! You know, I should have Google'd for something like that...