Good Designs for the Firebox?

I have been thinking of Firebox designs lately, and I really do not know what attributes affect the efficiency.

For one, what angle do you want the back wall at? I have always seen a ramp up to the flue area, but never seen any explanation of what shape this ramp should take.

Also, are their fixes to the front pans running fairly cold? Can the Firebox be built underneath the flue area as pictured? Maybe with the air intake moved from the front of firebox to the back? I know I have seen forced air mounted to the back of fireboxes, but I have not seen the internal design on these models.

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Do some research, try to find the thunderbolt evaporator project. I wish I could find my printed copy, it explains many of the ideas that you are trying to figure out. Air under fire and Air over fire work, fire box design can vary depending on what you are trying to accomplish. Control mechanisms for the above mentioned AUF,AOF are highly recommended.