Firebox Questions

[Malcolm B]

I'm beginning the planning for my build. I plan to use an 80 gallon air tank for the CC. I was just wondering if I could get some ideas for the firebox.

I read through the calculator that daveomak posted. Because my build will be an RF style, I was using the calculations he provided. I have some questions about the firebox though.

1) I believe I read somewhere in these forums that the best shape for a firebox is to build it tall, rather than square. (Though I can't find that link now). Anyone have experience or comparison from either tall or square FB's?

2) The firebox should be 33% minimum. But in your experience, is there an ideal or maximum number as well? I'm trying to consider the capacity that could be lost from ash accumulation on long cooks?

3) Is the pie vent the preferred intake design for the bottom of the FB?

4) What thickness of steel is best? I was thinking 1/4", but am now second-guessing myself as I wouldn't want a severe heat loss. Is it better to be thinner and insulated or is thick steel just fine?

I'm sure more questions will come to me, but I would appreciate any feedback. Thanks!

 

[daveomak]

IMO, these air inlets provide the best control of your smoker.....
1/4" steel works well... You can always insulate it later if needed....
FB... Tall to collect ash... Long to allow for a good mix of smoke and heat.. and to consume creosote from the extra air entering the upper air inlet..

 

[Malcolm B]

IMO, these air inlets provide the best control of your smoker.....
1/4" steel works well... You can always insulate it later if needed....
FB... Tall to collect ash... Long to allow for a good mix of smoke and heat.. and to consume creosote from the extra air entering the upper air inlet..

View attachment 399915

Thanks for the input! I'm a ways away from starting my FB, but I can work on the design and dimensions in the meantime using your input.

 

[AllTuckerdOut]

My firebox is 30" tall x 30" deep x 40" wide and it works great. I went 40" wide to match the width of the tank.

I have an Ash pan that's about 6" off the bottom of the box. I've done 2 cooks on it and it isn't full yet.


https://www.smokingmeatforums.com/t...ave-some-questions.286680/page-4#post-1976008

 

[Malcolm B]

My firebox is 30" tall x 30" deep x 40" wide and it works great. I went 40" wide to match the width of the tank.

I have an Ash pan that's about 6" off the bottom of the box. I've done 2 cooks on it and it isn't full yet.

Thanks for the input! I checked out your smoker in the link provided, - it looks amazing. Very precise and professional looking. How did you design your firebox for cleaning the ash? It doesn't look like the door is the full height of the firebox...

 

[AllTuckerdOut]

Yeah so the bottom of the firebox door is at about 6" high. That's also right where the grate sits in the firebox - the grate is expanded metal. The Ash pan sits right on the bottom of the firebox and slides right in. All I have to do is pull it out and dump it out.

This is probably the best picture of the firebox. I can get more tomorrow if you would like.

 

[daveomak]

Those air inlets look good.... They should give you some great control over the heat from the fire and moving heat through the CC....

 

[Malcolm B]

Those pictures are good. With the description, I can picture how it's supposed to work. I like the removable ash catcher design too.

 

[Malcolm B]

So I was about to order my firebox materials today and figured I'd check the fitment of my materials. I was originally going to go with a 18.54" wide, but this meant there would be a gap of about 6 3/4" from the bottom of the door to the top of the RF baffle. Design-wise, that didn't sit well with me so here I am re-evaluating. Keep in mind, the overall tank dimensions are now 24" diameter and 36" length.

1) Would welding the RF baffle to the top of the firebox inside the tank create a hot spot? Should I instead mount the FB slightly lower and install a baffle plate overtop of it and leave a gap to prevent that?

2) I've looked over other builds and notice how much higher up the firebox sits in relation to the bottom of the door. My original design of 18.54"x19"x19" would sit only 4 3/4" up from the bottom. Due to the awkwardness of this design, I have opted to change the baffle to any one of the following; 3" below center, 3 3/8" below center, 4 1/4" below center, 4 3/4" below center or 5 1/4" below center. (Mainly because the chords are incrementally easy to achieve). My biggest concern is that my tank, being 14622.3ci only requires 58.49in, but increasing the opening to 3" below center increases this opening to 147in. Is there anything else I need to consider before committing to an FB that is almost three times the recommended size?

Below I've provided a small picture of my progress and some numbers I wrote on the side of the tank, indicating my potential firebox mounting locations. I'm just not sure what works best and I'm hoping to get some more advice!



(I kept the lid and legs on so I can find center really easily. I'll cut them off later. I'm using the casters as a rotisserie that I will probably mount to the frame later for transportation of the smoker).

 

[daveomak]

Check your numbers.... Something is haywire.....

 

[AllTuckerdOut]

M Malcolm B what's the length of the bell on each side? From the weld to the outer most part.

 

[Malcolm B]

They are about 6.5" from the center of the weld to the outermost part of the cap. Thats what you were asking for, right? Also, the center cylinder section is 23.5".

 

[daveomak]

The opening for the FB/CC should be ~ 60 sq. in. .. Chord AB ~19.5" ..... and segment height ~5"... The green area is what the FB/CC opening looks like...
Mount the top of the FB 5 1/2" above the bottom of the CC... Take an actual measurement for the width of the RF plate... Weld the RF plate to the top of the FB... Cut into the tank past the weld seams for the FB install and ease of installation of the RF plate...



....Weld seam ....

 

[Malcolm B]

Ok. This is what I originally kept getting in my calculations. It looks a little odd with the top of the FB and baffle mounted about 6" below my cooking rack. Thanks for the clarification, Dave!

 

[daveomak]

Typical FB install...