# Fire Box Sizing



## deke77 (May 23, 2009)

I'm beginning my first home made smoker. I want to use with either wood or charcoal and I have a 60 x 30 tank for the cooking chamber. What is a good rule of thumb for sizing the fire box? I didn't want to build one too small but I also want to be fiscally conscious and not over-size if I don't have to. Any suggestions?

Thanks,

Deke

ECB with AfterBurner
Brinkman Smoking Pit


----------



## bigsal51 (May 24, 2009)

1/3 the size of the chamber


----------



## jamesb (May 24, 2009)

1/3 size of cook chamber is a common rule of thumb, but not always practical. For instance, on my 8' x 48" pit the firebox is only 30" x 24", on my 8' x 30" reverse flow the firebox measures 30" x 26".

On your pit, I would go with about 30" x 24"... Just guessing here...

Best of luck with your build!


----------



## randy1439 (Nov 25, 2010)

I'm so confused I'm building a return flow smoker, my tube is egg shaped, measures 21" high inside, and 28" wide inside, and gonna be 8 ft long. I'm still not sure about size of firebox, and size of smoke stack, I tried that pitt calc. still not sure if I did it right, any help with this whould be great.


----------



## randy1439 (Nov 25, 2010)

I come up with 27.5" x 28" firebox and still working on stack size and draft for mine.


----------



## randya (Dec 2, 2010)

This is a great tool to use too.  I have built a few and used this to size it.  Post us a few pictures of the build.  We all love to watch it being built.

http://webpages.charter.net/tomchism/BBQ CALC Forms/BBQ Smoker Calculators.htm

Good luck!

Randy


----------



## randy1439 (Dec 4, 2010)

Thanks, when I get it going, I'm sure you will be hearing from me. (help me, help me) lol.  I will try to get pics on here too. thanks for the info.


----------



## tom37 (Dec 4, 2010)

randy1439 said:


> I'm so confused I'm building a return flow smoker, my tube is egg shaped, measures 21" high inside, and 28" wide inside, and gonna be 8 ft long. I'm still not sure about size of firebox, and size of smoke stack, I tried that pitt calc. still not sure if I did it right, any help with this whould be great.


The pit calc may be hard to get good numbers from on a tank that isnt round or square.

I think I would take the 28" wide number and use it as if the thing was round and not egg shaped. Its going to make the numbers a little high but you can always damper down vs if you make the holes to small you can only open them so much.


----------



## randy1439 (Dec 4, 2010)

I ran a tape measure around it, and found a barrel the same measurement around, so I came up with, if it was'nt egg shaped, it would measure 26" inside diameter. But you are right, I can't see where I could go wrong if I just go with a size that I know is bigger than I need. Thanks again don't be afraid to shout out, I'm always open for opinions.


----------



## randy1439 (Dec 14, 2010)

I got a question ? On a return flow smoker, mine is gonna be 6 ft long, I decided to down size it a little. When i put the plate in for the smoke chamber, how much space at other end should I leave open, for the smoke to go up through and return.


----------



## tom37 (Dec 14, 2010)

I made mine a few more square inchs then the opening from the firebox to the cook area.


----------



## randy1439 (Dec 14, 2010)

Ok thanks, that makes sense, I was'nt sure about that, so figured I better throw that out there.


----------



## sqwib (Dec 16, 2010)

Randy make sure to post pics of your progress and talk it up, sometimes a mistake will be caught before its made.

I know when I built mine, its success was mostly due to the good folks on several forums.


----------



## randy1439 (Dec 16, 2010)

Oh I will, I sure I'll be needing lots of help from everybody, I did'nt get started yet, I'm only getting started cutting parts, It will be a while before I get started with the build part, but thanks for taking intrest.


----------



## randy1439 (Jan 2, 2011)

Im thinking about putting a smoke stack on both ends of my return flow smoker when I build it, because I think if I don't when I open the door to check on what i'm cooking, I think smoke will be pouring out in my face. So i think if I had another stack on other end, that I can open up when I open door it will cut down on all the smoke. Would this be a good idea or not.


----------



## randy1439 (Jan 2, 2011)




----------



## tom37 (Jan 2, 2011)

I would only do it as a place to dump heat or increase the draft in the event of low temps and you want to build the fire fast.

The smoke is going to follow the path of least resistance. That said unless you install an evacuater fan its gonna end up right in your face.

One thing that will help is don't mount the rig to low, smoke rises.

I like to be able to hold my arms out straight in front of me and work on the top shelf.

Just like my tables, my smoker is not short people user friendly. It only works for us tall lanky folks.

I'm not pickin on the short peps, sometimes it really sucks being tall. Trust Me.


----------



## randy1439 (Jan 3, 2011)

Yeah, I didn't think of that, mine gonna be mounted pretty high too, thanks.


----------



## randy1439 (Jan 10, 2011)

Being my tank is odd shaped,from the fire box to the smoke chamber I need 129.02 sq inches, the pit cal. does not show me what i need to know. If my tank is 28 inches inches high and it's 21.5 inches wide, if I just go with a 1/3 of the size for the smoke chamber. Which means the plate will lay in about 9.33 of a inch from the bottom, will that give me enough for the smoke chamber, I have know clue how to figure out how many square inches is in something D shaped.


----------



## tom37 (Jan 10, 2011)

If you make the opening from the firebox to the cook area 20 inchs wide by 9.33 inchs deep and its a sideways D shape you will have an area of  143.93 sq inchs.

If you make an opening 18.5 inchs by 9 inchs tall in the center you will have an area of  129.81.

Just making sure this is what you are talking about. The half circle area is the number you need to be close to 129.02. Correct? And also is this kinda what the end view will be on your smoker or is the egg part laying down?


----------



## randy1439 (Jan 10, 2011)

Yes, thankyou, only the right side going up is flat, but I think I can work from this, thanks again.


----------



## randy1439 (Jan 12, 2011)

A question about paint ? Is there a high temp. paint that I can spray on my smoker when I get it done, if so do I use a sealer or primer.  I would'nt think I could spray paint on bare metal.


----------



## sqwib (Jan 14, 2011)

I have had great success with VHT


----------



## randy1439 (Jan 14, 2011)

Yeah but, mine is gonna be 7 ft long and over all length from tongue to end of firebox is 15 ft. That will take a lot of spray cans, I'm kinda looking for something I can spray with a gun.


----------



## bob1961 (Jan 14, 2011)

randy1439 said:


> I'm so confused I'm building a return flow smoker, my tube is egg shaped, measures 21" high inside, and 28" wide inside, and gonna be 8 ft long. I'm still not sure about size of firebox, and size of smoke stack, I tried that pitt calc. still not sure if I did it right, any help with this whould be great.


you can use 24.5" x 24.5" avg from the 21" x 28" as your guide line for tank dia....it might be excat but closer to what you have with 21 x 28.........bob

....


----------



## randy1439 (Jan 16, 2011)

Question about the damper? Does it matter where it goes on the pipe, far as near the bottom or toward the top. Also I was gonna put one at the entrance from the firebox to the smoke chamber, Is this nessesary or maybe do one or the other, just in need of another opinion. Thanks


----------



## tom37 (Jan 16, 2011)

Randy, you may think about making the stack damper at the top, with a adjustment that can be changed by reaching up to the base of the stack. This would allow you to use the damper on the stack as a lid when not in use.

I myself think a damper between the firebox and cook chamber is a great idea.

If you have the doors open for an extended time the fire is going to really crank up from the extra draft. With a damper, you can close it if the doors are going to be open for a long time.

It will take longer to snuff the fire then the time it will take to crank up to a rage.

Not that its a good thing to have the doors open and loose all your heat. But there are times it happens.

I would love to build a rig that had linkage to slide a damper shut on the fire to cook area as I opened the lid. (open the door and the damper will close and vise versa)


----------



## randy1439 (Jan 16, 2011)

Ok, that answers that, Thankyou.


----------



## randy1439 (Feb 19, 2011)

I need some help with the pit calculator, I don't understand the air inlet opening, my firebox is 28x24x24 I want to go with a circular air inlet. If I want the opening to be 6" it says number of openings needed to match above is 1.74 (what is that?) then above it says air inlet openings needed is 49.25 I just don't get this, what I guess I'm trying to find out if 6" is to big or to small? do I need one on both sides? what size do I cut the slots into the firebox, do I need one or four?  This is the last thing that has me puzzled, if somebody can help me with this I will be in good shape the rest of the way to finish.

        Thanks Randy


----------



## tom37 (Feb 19, 2011)

What its telling you is that you need 1.74 openings that are 6" round. Or that you need 49.25 sq inchs of air intake. I have a template for the circle type vent I will try and find and post it, I believe that I have the sq inchs of my openings. Maybe that will help.


----------



## tom37 (Feb 19, 2011)

If I have done the math correct I believe that the openings add up to about 16 sq inchs while the vent is wide open.

So I would say that just a rough guess that you will need at least two similar to this one if you were to make the openings as large as possible and still be able to close it off. Like maybe making it where there is 1/8" instead of 1/2"  Area of an 8" circle is just over 50 sq inchs so having two would cut it really close since you only get half the area per vent of this type.


----------



## randy1439 (Feb 19, 2011)

Hey, thanks a million, you explained it perfectly so I can understand it now, Thankyou very much.


----------

