Double Plating Top of Firebox

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gary s

Gone but not forgotten. RIP
Original poster
OTBS Member
Jan 6, 2011

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  • 2,795 Posts. Joined 1/2011
  • Location: Whitehouse TX (East Texas) just south of Tyler
  • Points: 54

Question to: Ribwizzard 

I remember you saying in another post that double plating the top of the fire box was one of the single things you should do.

Are you using 1/4" for both plates with an air gap in between  What do you think about using high temp insulation between plates.

The main reason for the question is I am going to double plate my existing RF, we had some insulation left over from a Vertical, Insulated RF build. Was wondering if it was better with or without? I will post pictures as soon as we are ready to start.

Gary S
I've never used insulation in the firebox, so I don't know much about it. I'm in Florida, so not much need for it. I use 1/4 inch plate for both, but 3/16" would work fine as well, just don't seal it up completely, I just stitch weld it so no pressure builds up.

Mainly, I started doing this to keep the paint from burning off of the top of the firebox, and so I don't loose as much radiant heat out the top of the firebox. And it works really well.
Another thing is, a lot of builders extend the top of the firebox into the cook chamber, and attach the reverse flow plate directly to the top lip of the firebox.

I learned that all of the heat coming into the cook chamber will creat a hot spot at that end of the cooker. By double plating with a air gap, and attaching the reverse flow plate to the top plate, this helps eliminate that hot spot. You still need to attach a deflector plate to the lower lip though.....see my current build, I did it a bit different this time, but the basics are still the same.
I did extend the plate into the cook chamber, but I butted the RF plate up to it. I may modify that as well.


I will double check 

Even a piece of 3/16" with a 1/2" air gap would be worth doing if your fighting for space, but you might want to plug weld it in a few spots to keep it from warping too bad. How tall is the firebox? As you probably noticed, I like to build them tall as I can fit in the build.
I'll measure tomorrow,  when we built it we used what we had laying around, only thing we bought was expanded metal, First RF my #2 son and I built.

Learned since then if you need something go buy it. He is in the steel erection / metal building / concrete business he usually has a good bit of left over so don't really have to buy much. We are going to do the mods on mine and his smoker. when he slows down, we have two tanks waiting to become smokers, try to make each one a little better.

Firebox is 16" tall

RW my firebox is a total of 4,074.33 c i   if you look at my avatar you can see it is not a typical FB, I wanted something really different, combination of round, flat and square. My Fb to CC opening is 

30.940 sq. in.  according to Feldon's should be right at 31 sq in  so I am pretty close not over just a tad under. I did re measure my air inlet openings in the door I have 3 - 2"  9.4248 sq in  really should be 11.62 sq in  easy fix, (really have not experienced any problems with a little under size) after it gets going I have to dampen them back anyway. Not sure if I should add the additional plate under the RF plate ? What do you think. Still going to add additional plate on top of FB, may not insulate probably do as you suggested. The two things I wanted to accomplish was counteract the heat loss from the top of the FB and not have to repaint it so often. I think I may put an additional vent higher up in my door to help with the air flow from the FB into the CC as you and Dave have suggested. Like I said before it cooks really good no complaints, but I see all these different ideas and how well they work and want to tweak mine a little more.

Well, looking at your firebox, and reading your measurements, I wouldn't do anything inside the firebox, ....but looking at your build....looks like it's begging for something to sit on top of that firebox. Maybe something like a real nice small charcoal or even propane grill fabricated to blend in with the rest of the look you have going on there. Adding something like that would serve the same purpose!
Never thought of that ?   Hmmmmmmmm !

Hey this is for everybody, comments, suggestions, questions ?    

Gary, check the FB temp. when the smoker is running and holding good temp in the CC.... It should be about 100 ish or so warmer then the CC.. If it is warmer than that, you could use some air movement to move the heat into the CC... at least that's what folks have related to me... The upper air inlet will accomplish that temp change without too much work and expense..
Thanks Dave, I think I am going to do that,  With all I have read and everyone has talked about, I don't think it could hurt. I have written to a guy who specializes in heat transfer (don't remember the technical name)  He said insulated fire box is the way to go besides efficiency with heat and fuel it also reduces creosote build up. He said adding the plate to the top of my existing smoker would help, he said with a 1/4" air gap and stitch  welded (not solid) I could expect a 5 to 10 percent improvement, he said again, insulating was the best way  and recommended mineral wool for insulation.

Still debating, may go ahead to see if I can tell a difference 

Apology to everyone, if I have seemed a little mater of fact or cranky, My best friend of over 40 years had to have brain surgery that resulted from a surgery he had back in 2000. He is an avid hunter and fisherman, and now can't be left alone and doesn't remember who came to see him yesterday. Just keep him in your prayers

Thank you

Just ordered an I R thermometer , Should have already had one,

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