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-   -   Offset Firebox Design ??? (http://forum.texasbbqrub.com/showthread.php?t=39808)

SpicemasterBob 05-04-2010 09:56 AM

Offset Firebox Design ???
Did a little research and couldn't find an answer that fit my question, so I thought some of y'all could help.

We're building an offset smoker that's made up of (2) 24" lengths of sch. 40 pipe. We are trying to determine what is the ideal size opening from the firebox to the smoker side. The smoker box will have just a single grate with tuning plates positioned approximately 3" below that surface. I understand that good airflow is critical to the design, but I'm a little confused as to the size of the opening into the smoker box and the ideal distance of the opening to the grate/tuning plate level.

Please help with your suggestions and/or opinions.

la coonass 05-04-2010 04:13 PM

Pit building calculations
I'm a newbie and wanted to know size of firebox in relation to the cooking chamber and size opening from inlet to firebox and from firebox to cooking chamber. These guys on this forum are great and will all give a hand when they can. I found the pit building calculations on another forum, but I'm not sure if I can post that info on this forum, If someone would let me know how to get that info to you I would gladly do it. Can we post email addresses here is another question I have Thanks in advance

cappy 05-04-2010 05:54 PM

Aperture size from firebox to smoking chamber:

On my pit (20x52" smoking chamber), the aperture is 15" wide by 5.5" tall, like a semi-circular piece of pie completely cut from the bottom side of the smoking chamber. There is a semi-circular baffle (essentially the part that was cut out), angled from the top edge and protruding into the smoking chamber to deflect heat and smoke initially to the bottom of the pit. See this picture:


You can also see an example of an angled baffle from the smoking chamber side in Simon's second picture in this thread:


As far as the location of the tuning plates is concerned, I don't have them, but on a 24" pit I would think they ought to be further away from the cooking grate than 3 inches.

See this thread:


And this one where PitBull experimented to find a way around his radiant heat problem coming from the plates:


As far as the question la coonass had about firebox size, 20x20 square or 24x24 are pretty common sizes. I have a 20"Wide x 24"Long square firebox on my 20x52" Klose which also has an upright on the end. That size firebox is more than sufficient for the pit. It had plenty of room around the fire.

See this thread for examples showing my fire size:


SpicemasterBob 05-05-2010 12:07 PM

Thanks Cappy!! A ton of great info, much appreciated!

SpicemasterBob 05-07-2010 01:10 AM

Our firebox runs the length of the pit as it is mounted parrallel to the main chamber. We can get get approximately a 6-7 hour 340 +/- degree burn in moderate temps and low wind conditions without ever opening the box. We light one end with a torch and strategically place mesquite sticks along the sides to smoke as required and use carbon or Kingsford when we are after just heat.

I agree that when you open the doors with more frequency the quality of your product suffers.

Thanks again for the input, please stop to say hello if we are ever at the same event. We are Piping Hot BBQ

Teddy N Texas 08-02-2010 07:59 PM

Thanks Cappy for all the good info. I have never added wood with just a 10* drop in temp. That could be why I have to fight so hard to keep the temp up. I will try adding wood as you suggested the next time I cook.

WestCoastSmoke 08-04-2010 11:12 PM

Try this site:


bigwheel 08-05-2010 05:16 PM

Well I would put the cook chamber on top of the firebox. That saves a bunch of steps and conforms closer to the laws of physics as concerns the old hot air rising deal. Should
make it a bunch mo fuel efficent than trying to force it to go sideways. Hot air do not like to act like that.


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