How much of the fire box is air?

[BigButzBBQ]

I was putting together the final plans for the construction of my new rig made from a 500lb propane tank I had pretty much planned on doing a lang style offset with it.
I got all my numbers together and was figuring out exactly how big to make the firebox and how it should be attached to the tank and then a thought occurred to me, The tank is 10 feet long. and has a 36 inch diameter with rounded ends on it. The central cylinder is a total of 7 feet in length with each round end sticking out about 18 inches. Basically, I have alot of room to play with, so, the thought occurred to me that if I went 2 feet in on the main cylinder and made half of it the fire box and the upper half a grilling/cooking area, would it work. Now mind you, I want there to be enough room in the smoking chamber to do a whole hog if I need to. But, when I figure out the space that the fire would be taking up, it didn't fit the ratio, however if I counted the cooking area in w/ it, then the numbers work out just fine so, that leads me to the question.

How much of the firebox is just for fire and how much is for air?

Also, as a side question would a reverse flow still work on only 5ft long cooker?

Any help on this would be greatly appreciated.

 

[Divemaster]

I think your basic design for the fire box would work fine. I know on my Lang, the box is roughly 18"x18"x24" with a door that allows me to feed from the end.

As for the cooking chamber, Ben makes them as small as 48" long.

 

[antoant]

How much of the firebox is just for fire and how much is for air?

What do you mean by that?

 

[BigButzBBQ]

What do you mean by that?

The fire box is designed to provide the right mixture of heat and air flow given a smokers size. The fuel needs air to burn, of course but, the volume of air within the fire box is also heated and travels into the smoking chamber. I basically would like to use some "air space" if possible to put grilling racks in, but, I don't want to cause issues with my smoking chamber by doing so.

 

[BigButzBBQ]

This is a sketch at what I'm thinking of for the design.

 

[antoant]

So are the smoking and indirect grill area connected? Do you think you will be able to reach the temps required for grilling using just indirect heat?

 

[BigButzBBQ]

So are the smoking and indirect grill area connected? Do you think you will be able to reach the temps required for grilling using just indirect heat?

The smoking and grilling area would have had a wall between them with only a duct out through the fire box into the smoking chamber. I believed the grill would have gotten hot enough. The design was initially created to save on some materials and trailer space.

This design, along with my last two, has been scrapped and it's been decided to go more with a lang type style. I'll make sure to show the build progression though in later threads.