firebox size

[dmike25]

I'm building an offset with tuning plates, my first build.
24"d x 44" long. 1/4" wall pipe, 3/8" plate ends. 4" X 36" chimney already on.
It will have a square firebox, with the door on the end, and the intake in the door. If I make the box a 20" cube, it will be 20% oversize according to Feldon's calculator, which I think would be okay. I don't know why, but I keep thinking that I should make the firebox longer, 20" X 20" X 22". According to the calculator this would be about 33% more than needed. Is 33% too much oversize?
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Mike

[k.a.m.]

The firebox will work at 20" Sq.
It will also work at 20" x 20" x 22".
The difference in one or the other is which ever one you choose you will not know how the other would have worked with the cooker, you will learn how to operate the cooker with the chosen dimensions.
Go with your gut feeling on this, you evidently have some reasons besides being too small for the chamber. To satisfy these reasons and sleep at night build it slightly bigger.
I hope this helps.
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Always remember slow and steady wins the race.

Hybrid Cooker

[dmike25]