Firebox Size, 1/3 of cooking chamber or smaller???

[dnomode]

Hello Everyone,

I'm getting ready to build a pit using a custom 610 gallon propane tank and i'm confused about the firebox. I've read that the firebox should be about 1/3 the size of the cooking chamber and I've used the calculator to figure out the size of the firebox and it should be about 34" x 36" x 40".

However Im confused because I took a little tour at franklins bbq and his fireboxes are way smaller. Im estimating about half the size of the Feldon Calculator recommendations (he told me he was using a 250 gallon propane tank cut in half). What the difference between a large firebox and the smaller firebox? Why is Aaron using the smaller size?

Thanks for the info.
Edmond

[k.a.m.]

What the difference between a large firebox and the smaller firebox?

One is larger than the other.

Why is Aaron using the smaller size?

Because he can and wants to.

First let me say that the calculator was created and used as a tool to help folks build a cooker that will work, it should not be considered a bible.
I have been building and fixing folks cookers for over 20 years and in that time I have seen cookers defy every aspect of the calculators numbers for size and proportions. Aaron builds his cookers the way he does because for him they work as he wants them to. Are they the most efficient? I don't know he may think so and that is all that matters.
In my experiences smaller fireboxes consume more wood because of the exchange of heat for fresh air is more frequent than using a larger firebox which can hold a larger volume of heat. In my opinion you can also go too large on the firebox which will change the way the cooker drafts.
Most cookers will work once you get used to operating them. Most of the lack of fuel efficiency on a cooker is not because it is insulated or not it is because the cooker is not sealed well enough and poor design as far as firebox to cooker chamber openings, exhaust size and placement, lack of intake,those sort of things.
The next cause is operator error meaning the person using the cooker does not know how to make the cooker perform to its potential.
I ran your numbers by the gallons given, I prefer working with dimensions over gallons but this is what you gave. I would feel comfortable running a 36" square firebox, it is a bit smaller than recommended but will work.
I hope this helps.