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.

 

[BigW.]

I do not have an offset, therefore my my opinion is not worth much. I'm not sure you gain much with the fire bricks other than weight and maybe wait. Waiting for the fire bricks to heat up may delay cooking start. I'm sure once they are hot, they'll retain heat.

Do you have some sort of fire basket? Those seem to be pretty popular to get fire off the bottom.

 

[civilsmoker]

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 ...

This you want at least 1/3, however, more isn't a bad thing at all. If your fire box is to cramped, it will affect combustion and can increase the potential for a dirty smoke. If you want to experiment putting split (1.5-inch ones) fire bricks along the back would be the place to put them, then on the bottom. Note that the bricks will take energy to heat but once hot the retained heat will help even things out. Usually a 1/4" fire box has enough with the steel itself.

Just know that the smaller you make the fire box the more sensitive it's going to be to air settings and such........If it works right now.....I personally wouldn't change a thing.....

 

[luvcatchingbass]

My first offset that I ever ran and only one I own is a Oklahoma Joe that is half offset and half propane. The fire box and the cook chamber for the smoker/charcoal grill are the same size, the one thing I did play with is taking various widths of plate steel to make baffles basically and a deflector. I haven't used it for a few years now especially after the pellet grill, still have not got near as good of BBQ results on the pellet than that little offset but the pellet is convenient for the current lifestyle. Learned a lot about fire management with that little guy.
There are lots of other things a guy can easily tweak with than altering a cooking chamber size. In theory if you want less "chamber volume" for the fire to work put some fire bricks or something in there till you decrease the "volume" that the fire has to work with.
One of my struggles was if I wasn't careful I could run mine much hotter than I wanted and if sometimes would struggle with keeping a good coal bed with a smaller fire.