Julie, that needs a correction. 1:2:3:6 which means.... 1=system size, in your case 12in. Now plug in to the previous ratio, 1, system size, 2, j tube height 3, burn tunnel length, 6, riser height. Which puts you at 2 ft x 3 ft x 6ft, approximately of
course. So your barrel would be be a hypothetical 6 ft tall 3 ft wide. To make this more accurate.....this is the math for a batch system...
1. Decide what system size you want and name your DIAMETER of chimney flue.
2. Then use equation to calculate the Cross Sectional Area(CSA) of a chimney flue:
The formula to calculate cross sectional area of a cylinder is pi (a constant value, approximately 3.14) multiplied by the radius of the cylinder (half the diameter, so half the distance from on side of the circle to the other) squared (multiplied again by itself) So if the circular end of the cylinder is 12in across then the diameter is 12in and the radius is 6in. The cross sectional area would be calculated as: 3.14 x 6in x 6in = 113in sq.
3. Now solve the following equation (insert CSA of chimney flue and calculate)
Y = square root of (CSA OF CHIMNEY FLUE) * 2 / 3
4.Based on Y you can derive the dimensions of firebox (without slopes - these you will add in the end)
FIREBOX:
WIDTH= 2 * Y
HEIGHT= 3 * Y
DEPTH or LENGTH= 4 * Y
HEAT RISER:
HEIGHT= 6 * Y
CSA: if SQUARE, then one side of a square is the same as the DIAMETER of a chimney flue!
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EXAMPLE:
1. I want the system for a chimney flue with DIAMETER of 12in.
2.
(CSA OF CHIMNEY FLUE) = PI times the square of the radius
(CSA OF CHIMNEY FLUE) = 3.14*6^2
(CSA OF CHIMNEY FLUE) = 113in sq
3.
Y = square root (CSA OF CHIMNEY FLUE) * 2 / 3)
Y = square root ( 113 sq. In * 2 / 3)
Y = square root ( 75in)
Y = 8.5in (roughly)
4.
FIREBOX:
WIDTH= 2 * Y = 2 * 8.5 = 17in
HEIGHT= 3 * Y = 3 * 8.5 = 25.5in
DEPTH or LENGTH= 4 * Y = 4 * 8.5 = 34in
HEAT RISER:
HEIGHT= 6 * Y = 6 * 8.5 = 51in
So with a 12 inch build, the system would top off at 6'4 just as a box and riser.