Step into the Octagon!

[FredyzBBQ]

First of all, the Pit Calculator is amazing. I just wish the calculator was more Octagon friendly.

I found a good calculator to calculate the volume in gallons but then for the firebox I had to manipulate the numbers to match the gallon volume. This thread may or may not get long so I'm going to put my numbers and the calculator results in this first post then ask my questions in the second and hopefully all you experienced people have time to review and respond with your thoughts.
Calc results.

• My firebox is considerably oversize.

• Throat is also considerably oversize but I hear that is not an issue on a offset.

• Intake is considerably oversize but not an issue since it can be closed down as necessary.

Cook Chamber Size: 18" Octogon

1 side of 8 for calculations 7.5"
Calculator I used for Octagon Area, not volume.
https://www.google.com/search?q=Octogon ... &newwindow

18"x18"x38"
area = 271.6 sq. in.
Length x 38
------
10,320.8 cubic in. volume

44.678 Gallons
------------------------------------
Firebox Size: 18" Octogon

18"x18"x18"
18x18x15.08 square in calculator
area = 271.6
length x 18
------
4,888.8 cubic in. volume

21.163 Gallons
____________________________________

Throat current: 60 Sq. In. Area
____________________________________

Stack: 7.33 Sq. In. Area
Length: 1 29/32"
1.906"
Width: 3 27/32"
3.843

Recommended length: 34"
-----------------------------------

Intake 19.62 sq. in.

5.81 x 13.23 = 76.75 63.2

[FredyzBBQ]

I suppose my biggest questions are about the throat and firebox sizes based on the above info.
Also see the screenshot of the end view of the cook chamber.

• What are the biggest issues and drawbacks to my firebox being so much bigger than the calculator calls for?

• I'm thinking about making it a reverse flow but because of the enlarged throat, will that be an issue?

• The green line is a cooking grate, is there even enough room for a RF Baffle Plate? From the top of the FB to grate is 3.5".

• How will the oversized FB affect a Offset vs a Reverse Flow unit? Or what will it do to each?

[dacolson]

With so much extra air in the FB, you’ll have a harder time keeping control of your fire and coals. Too much wood and it gets hot in a hurry. Too little and you’ll burn through your coal bed super fast. Close the vents down too much and you smolder. Just harder to set it and forget it.


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[FredyzBBQ]

With so much extra air in the FB, you’ll have a harder time keeping control of your fire and coals. Too much wood and it gets hot in a hurry. Too little and you’ll burn through your coal bed super fast. Close the vents down too much and you smolder. Just harder to set it and forget it.

That's good info Dave, the kind I'm looking for, thanks!
I thought about cutting the end off the FB to make it more the right size. However I'm struggling with that idea, because on the first build I put a cook grate and top door for hot grilling steaks etc. too. If I shorten the box it would be too small I think for that feature still. I've heard of people cutting a plate and welding in their firebox to make it smaller volume by eliminating some cubic inches of space.
I really need to get over to my buddy's house who I built the first one for (he loves the firebox grill and says he uses it all the time, more than the smoker) and see how his is working out, but it's an almost 4 hr drive.

[Dirtytires]

I have to wonder why guys constantly run the numbers and then ask if they are important.

As always, you are free to build whatever you want but if I were going to spend a 100 hours and $2000 on a pit I would want it to work.

[FredyzBBQ]

I have to wonder why guys constantly run the numbers and then ask if they are important.

As always, you are free to build whatever you want but if I were going to spend a 100 hours and $2000 on a pit I would want it to work.

Well, because the design works after one fix, elevating the fire grate that was originally 1" off the floor of the FB.

This is despite the over-sized FB, the fact the stack is near the top on the opposite end and being an offset without any kind of throat or stack baffle.

I suppose I was looking for a more experienced and complex answer as to why I should fix something that isn't broke.
I will continue to think out of the box and as any Patriot would, "for myself"!

[Big T]

I suppose I was looking for a more experienced and complex answer as to why I should fix something that isn't broke.
I will continue to think out of the box and as any Patriot would, "for myself"!

I've always been told that if it ain't broke, don't fix it.

[FredyzBBQ]

I suppose I was looking for a more experienced and complex answer as to why I should fix something that isn't broke.
I will continue to think out of the box and as any Patriot would, "for myself"!

I've always been told that if it ain't broke, don't fix it.

I'm going to have to agree with you Big T.
After all I've read about offset baffles, smoke stack position on CC and firebox sizing, I may have overcome the calculator. I built the first one thinking that the heat would pass evenly through the cook chamber traveling from lower right throat to left upper level stack by laws of nature. I think the draw is good enough that it must pull the heat from side to side sufficiently. The first thing smoked in it was a 17lb Turkey with Cajun Injection and it came out perfect.

Maybe because my smoker is not so big (it was designed and drawn to maximize the use of a single 4x8 sheet of steel and was very successful with that factor leaving almost no usable scrap except to build a grease dam), it's not as susceptible to the calculator factors on the firebox. I think on this second one I'm going to lower the stack to grate height and tack in a baffle to get more of that "cook from the top down effect" and see how that works, like the guy that runs this site and SmokerBuilder podcasts talked about in his recent podcast comparing RFs to Offsets. I think that video is what prompted me to examine my design as I didn't feel like it was cooking either way he described, top to bottom or bottom to top but rather more evenly. I'm thinking that possibly how the RF cooks from bottom to top is most desirable and my whole reason for writing this whole thread with all the info and screen shots of drawings is to think more about making it a RF smoker, to get that bottom to top cooking.

What do you think about the space between the top of throat (unfortunately I can't move the throat down and it will be the deciding factor it seems as to whether or not I make a RF or Offeset this time) and current level of the grate? Do you think it would leave enough room for a BP and being no bigger than it is, if the BF was made from 1/4" do you think it would need a shadow plate under it? Should the grate be raised? etc...thoughts?