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-   -   Firebox question (http://www.bbq-brethren.com/forum/showthread.php?t=150754)

Qbert60 01-03-2013 12:59 PM

Firebox question
 
I hope I am putting this in the right section.

I have a trailer pit. The cooking chamber has a hexagonal shape to it (6 sides). It is 48' long by 36" wide. I am not sure how tall it is though. The firebox is a similar shape, but is extremely in efficient. I am looking to build, or have someone build a new insulated firebox. I am having trouble trying to figure out was size it needs to be though. I look at most pipe smokers and no matter how long the cooking chamber is, the firebox is almost always 20" x 20". I contacted a fabricator today and gave him a rough idea of what I want, but the size is still baffling me. Can anyone assist?

AustinKnight 01-03-2013 01:10 PM

This should help

www.feldoncentral.com/bbqcalculator.html

Sent from my SGH-T999

Bludawg 01-03-2013 01:32 PM

To be properly balanced th Fire Box interior should be roughly 1/3 the volume of the meat oven. Size matters!

Qbert60 01-03-2013 01:55 PM

Quote:

Originally Posted by AustinKnight (Post 2315456)
This should help

www.feldoncentral.com/bbqcalculator.html

Sent from my SGH-T999

SO I used that calculation and found the cubic inches of the potential firebox. But how do I convert that to length, width, and height? Sorry for not be a mathematician.

Zak 01-03-2013 01:55 PM

My stick burner is made out of an old 275 gallon oil tank and has a 24"x24"x24" firebox on it, which by the calculations on the website listed below is only 22% of the cooking chamber volume. I've never come even remotely close to not being able get temps over 400 easily with a decent sized fire in there. To maintain about 300, there's not much of a fire in there. A stick burner isn't like a wood stove where you pack it full of wood and damp it down, you want a small, hot fire. Granted i wish i got 12 hour burn times out of my pit like i do my wood stove but temp control is key with a pit. I'd say a 20"x20"x20" will absolutely be more than you need to maintain high temps. I'd say air inlet placement and design is much more critical, especially with an insulated firebox. Installing large, adjustable vents on a smaller firebox will give you a much better experience than a larger firebox with poor air flow. When i built my smoker i had no experience what so ever and just kinda wung it and learned from my mistakes but made adjustments as needed. I'm not expert but i know my pit's temp can get very high without even coming near the capacity of my firebox and keeping a temp of about 300-350 is only maintaining a small/medium fire.

Qbert60 01-03-2013 02:39 PM

Quote:

Originally Posted by Zak (Post 2315510)
My stick burner is made out of an old 275 gallon oil tank and has a 24"x24"x24" firebox on it, which by the calculations on the website listed below is only 22% of the cooking chamber volume. I've never come even remotely close to not being able get temps over 400 easily with a decent sized fire in there. To maintain about 300, there's not much of a fire in there. A stick burner isn't like a wood stove where you pack it full of wood and damp it down, you want a small, hot fire. Granted i wish i got 12 hour burn times out of my pit like i do my wood stove but temp control is key with a pit. I'd say a 20"x20"x20" will absolutely be more than you need to maintain high temps. I'd say air inlet placement and design is much more critical, especially with an insulated firebox. Installing large, adjustable vents on a smaller firebox will give you a much better experience than a larger firebox with poor air flow. When i built my smoker i had no experience what so ever and just kinda wung it and learned from my mistakes but made adjustments as needed. I'm not expert but i know my pit's temp can get very high without even coming near the capacity of my firebox and keeping a temp of about 300-350 is only maintaining a small/medium fire.

Current opening is about 6-8' wide by 3 inches tall. There is about 10 inches between the top of the opening to the cooking surface. I know the Jambo's opening from the firebox to the cooking surface is at grate level. Does that make a big difference?

Bludawg 01-03-2013 03:33 PM

I have never seen a Jambo so I can't speak of the engineering, heat rises. If the opening is to big you get a hot spot to small and it wont draft right. If the stack is the right diameter and long enough and positioned correctly that is 1/2 the battle to proper drafting the dimensions and placement are the flip side of a good cooking pit and must match the fire box output. If you increase the FB then the stack must be modified to match or you will have big temp differentials or low heat and billowing smoke. Use the calculator and round up!

AustinKnight 01-03-2013 03:47 PM

Give it to your fabricator, they will know what to do, if you build it ....people won't starve:D

Sent from my SGH-T999

Zak 01-04-2013 08:04 AM

Quote:

Originally Posted by Qbert60 (Post 2315556)
Current opening is about 6-8' wide by 3 inches tall. There is about 10 inches between the top of the opening to the cooking surface. I know the Jambo's opening from the firebox to the cooking surface is at grate level. Does that make a big difference?

My pit has an opening 4"x18" that sits about 2 1/2" above the floor of the cooking chamber which was about as low as i could get it. I did have an issue with a hot spot next to the firebox since the heat would immediately rise then work it's way over to the exhaust side. I cure that with a simple baffle bby taking a thin sheet of metal and putting it right over the opening from the firebox to the cooking chamber and that resulted in a difference of 10 across the entire thing, which is close enough. If you want to shoot me a PM i can email you pics of everything.


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