I have yet to see the formula or how big the firebox has to be for a 55 gallon drum with my searches on the forum. Anyhow, I plan on building one here very shortly and would like some help figuring out the dimensions to build the firebox so it doesn't get too hot, or too cold. Someone else on here had built a similar one and this is kinda what i want to build. http://i.imgur.com/oGrVp.jpg Does anyone know of some good plans to build this correctly? I am just too new at this whole thing to even know how big of a hole to make between the firebox and the drum. Anything would be helpful! Thanks all!