Offset Firebox thoughts

[FoxmanNC]

I have an Old Country Brazos 1/4 steel entry-level offset. It's my first stick burner, and I'm loving it, but if I can maximize its effectiveness within a reasonable amount, I want to. I was watching a video, and the guy in the video was saying that the ideal volume of a firebox is about 1/3 of the cook chamber. (I'm not a builder, and don't understand all the science behind these things) The 1/3 volume thing sent me down a bit of a rabbit hole. I ended up learning that the Brazos firebox is about 1/2 of the cook chamber. So, I went to chat GPT to find the optimal solution.

Two questions. Is 1/3 truly optimal? And secondly, does this solution sound like a good solution

According to AI, the optimal set-up using 4.5" x 9" x 1.5" firebrick would take 28 bricks. It suggested the following:
Floor 12 - 3 rows × 4 bricks; covers floor area
Rear Wall 8 - 2 rows × 4 bricks; vertical placement
Side Wall 8 - 2 rows × 4 bricks; opposite air intake
Why this layout?

• • Floor: Raises coal bed, retains heat, and provides a stable fire base.
  • Rear wall: Radiant heat reflection protects steel and distributes heat evenly.
  • Side wall: Insulates and helps reflect heat, maintains even temperature.

 

[Newglide]

No input here but following along.

 

[Smokin Okie]

This is all greek to me. I don't see how the volume of the firebox has much bearing on anything.

What I want is in a firebox is length, so I have the option of building the fire closer to the firebox door or closer to the cook chamber.

But hey, that's just me.

When I owned a Brazos, I lined the bottom of the firebox with fire brick only to provide some insulation and stop heat loss out the bottom.

 

[JckDanls 07]

Yes... They say 1/3rd is ideal... But a little bigger doesn't affect it one way or the other ... Is what I've been told by some pretty competent builders ...

 

[Dustin Dorsey]

I think that number was kind of an observation by some guys on forums that built pits. You'll see lots of well made pits that violate this rule. There was never some optimal calculation made. Now a guy did make a pit calculator based on those observations. I think people get those things confused. Hopefully, that makes some sense.

Also, the Brazos is a small pit and the larger firebox size helps the combustion gasses cool down before they get to the cook chamber. You wouldn't want to reduce it. Then you just have to build smaller fires.

 

[FoxmanNC]

This is all greek to me. I don't see how the volume of the firebox has much bearing on anything.

What I want is in a firebox is length, so I have the option of building the fire closer to the firebox door or closer to the cook chamber.

But hey, that's just me.

When I owned a Brazos, I lined the bottom of the firebox with fire brick only to provide some insulation and stop heat loss out the bottom.

I make a fire closer to the door for more air, or at least that is my rationale. Heat loss out of the bottom, sides, etc, along with steel integrity, makes sense to me for lining, also fuel efficiency. But, not being an engineer or science-minded, I'm just spitballing. I'm hoping someone in the know can offer an opinion. I do know that both the Franklin Pit and the Solution offset have fireboxes about 50% of the cook chamber, but they compensate for that in different ways. The Franklin is air-gapped insulated, but I'm not sure how the Solution compensates for the size of the firebox. Perhaps it is the scoop baffle that compensates for the size of the firebox; I just don't see that connection.

 

[Smokin Okie]

The calculator was Felton's Calculator

I ran those number for the Brazos and they never agreed. Same with the Franklin.

How they arrive at those dimensions, is as I said, all greek to me.