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Pit building ratio calculator
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Tom C
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Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Fri May 15 09 12:05 pm    Post subject: Reply with quote

That looks fine to me!

You can always measure from the top of the circumference to be sure. If it's a little longer you can use a domper. It's better to be a little long vs short on the stack.

Most people place the stack at or just lower than the lower cooking rack.

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Homemade offset smoker 24"x48"
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Smokin' Z



Joined: 20 May 2009
Posts: 1

PostPosted: Wed May 20 09 6:12 am    Post subject: Smoker Calculator Reply with quote

Very good information. I just wish I had found it 5 years ago. If I have already built everything, how do I know it's right. I hear about tunning your grill. How do you go about doing that? Also, I am going to be building another grill and wanted to use a prefab cast iron door and just weld it in to get a more professional look. Know where I could find one?
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Tom C
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Joined: 21 Jul 2007
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Location: N. California

PostPosted: Wed May 20 09 2:13 pm    Post subject: Reply with quote

Smikin' Z,

Yes, I was lucky to find this site and all the great information before I really got started. Everyone here really helped me get it done.

Tuning plates are used to adjust how the heat is distributed in the smoker. Below are the plates I made for my smoker. I started with six and adjusted the space between them to adjust the heat distribution. In the last six months or so I have only been using three of them to balance the temperatures on in the smoker. If you do a search of the postings here on the Ring you will find great posts of how the plates work.



Also, take a look at this site for a potential source for a door.

http://www.vogelzang.com/barrel_stoves.htm

Tom
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solanabeacher
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Joined: 28 May 2009
Posts: 429

PostPosted: Fri Jun 12 09 10:38 pm    Post subject: Reply with quote

I can't make this thing work. I have a 24" X 48" cooking chamber and a 24" X 24" fire box. This is round steel. How do I figure out firebox to chamber size, height of tuning plates, chimney size, ect. Can anyone help me out here? I got the pipe today and hope to fire the torch tonight.

THANKS!
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Tom C
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Joined: 21 Jul 2007
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PostPosted: Sat Jun 13 09 10:46 am    Post subject: Reply with quote

Here is how it should be read for a circular firebox:

Hope this helps
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solanabeacher
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PostPosted: Sat Jun 13 09 8:53 pm    Post subject: Reply with quote

Thanks again Tom!

-Bill
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zenbbqmaster
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Joined: 17 Jul 2009
Posts: 33
Location: Houston, TX

PostPosted: Sat Jul 18 09 7:33 am    Post subject: Cool Tool Reply with quote

Now that is interesting stuff!
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(281) 359-PITS (7487)
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Cody Pendant



Joined: 03 Aug 2009
Posts: 15
Location: Wild West Texas

PostPosted: Wed Aug 05 09 4:43 am    Post subject: Ratio Calc ?'s Reply with quote

Thanks for the spread sheet and the calculations.

Questions: Confused

1. Is the calculator based on internal or external pipe sizes?
(I.E.: Do I need to plug in the internal size?) My assumption is for internal size.

2. The firebox opening, how critical is it? My firebox opening is quite abit over the recomended. If, say it calls for 5 1/2 " opening, is it ok if it is larger or should I restrict it down to close to the recommended?

3. Is the measurement for the total length of the pipe including the bend (if there is one) or just from centerline of the 90* angle to the top?

Thanks for the help!
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Tom C
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Joined: 21 Jul 2007
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PostPosted: Wed Aug 05 09 8:17 am    Post subject: Reply with quote

Hi Cody,

1. I would say most pipe size is based on O.D. (external).

2. Not sure if you are talking the opening into the cooking section or the air intake opening but I would think larger would be fine. Smaller would be the bigger issue.

3. I think you are talking about the smoke stack here. If so, I would measure the length of the stack from the bottom of the bend.

Hope that helps.
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Cody Pendant



Joined: 03 Aug 2009
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Location: Wild West Texas

PostPosted: Wed Aug 05 09 6:09 pm    Post subject: Rule of all thumbs Reply with quote

Thanks Tom C.

I will try to clarify. Sorry that I was unclear.

1. Yes I agree that most pipe is measured by O.D. However, the calc figures volume for the pipe. Guess I need to figure that one out and compare.

2. I am asking about the firebox to cooker opening. It has the football shape and it is quite a bit larger than the recommended 5.5" one on the calculator. I wanted to know if it would benefit me to reduce it down to size.

3. I think we are on the same page here.
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Tom C
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Joined: 21 Jul 2007
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PostPosted: Wed Aug 05 09 9:34 pm    Post subject: Reply with quote

Hi Cody,

Yes, I guess the volume calculated would have to be ID volume. Also, a larger opening between the fireboxes and cooking section could be larger and would be fine. The concern is having enough air flow.

Keep in mind that the ratios and the calculator were meant to be a guide. Many here on the Smoke Ring have built very good working smokers with very different opening sizes. These ratios were meant to get people into the ball park so to speak.

Good luck with your build and keep us all up to date with pictures.
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Cody Pendant



Joined: 03 Aug 2009
Posts: 15
Location: Wild West Texas

PostPosted: Thu Aug 06 09 5:33 am    Post subject: Ball Park Franks Reply with quote

Thanks Tom C,

Ya, Ball Park is whut I wuz shoot'n fur.

I was just not sure if I was to plug in the size of the pipe O.D. or the size of the I.D. to get the correct sizing of length. Big difference in length, say for a 2.5 " pipe or the same but the I.D. at 2.25"


Appreciate the help! Wink
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Wreckless
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Joined: 15 May 2009
Posts: 2292
Location: New Braunfels, TX

PostPosted: Sat Aug 08 09 7:39 pm    Post subject: Reply with quote

Tom,
The calculator is an excellent idea! Now...How to use the darn thing? I have a circular 29" dia x 96" long smoker. The calculator tells me that even using an 8" pipe for the chimney, It would need to be 5' long. Is that correct? I could sure use a tutorial on the calculator. I have an offer. If I were to supply a drawing of a generic pit ( Firebox / smoker ) done on a spreadsheet as well, would you be able to and willing to add some A) / 1) type notes to it? I see a lot of questions here and would like to assist in making your calculator spreadsheet, as they say in the self help books.. " Pit calculator for dummies". Not to insult anyones intelligence other than my own.
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Tom C
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Joined: 21 Jul 2007
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Location: N. California

PostPosted: Sun Aug 09 09 1:29 am    Post subject: Reply with quote

Hello Wreckless,

I see the first issue in your calculations. The calculator is used to calculate the openings and chimney based on firebox size not cooking section size. Rule of thumb is that a firebox should be 1/3 the size of the cooker section.
In your case, your cooker section = 63377.76 in volume in cubic inches. Divided by 3 that comes out to 21125.9 cubic inches needed for a fire box volume.
Using that volume and assuming that you use a circular firebox, you would need a section of pipe 29" in dia and 32" long. Using that size fire box, your 8" chimney would only need to be 21" long. Also, the air intake for the firebox would be 52.8 sq inches and the opening to the firebox would be 169 sq in.
If you decided to use a square firebox, 29"x27"x27" would work and the air in take would change to 63.42 sq in. the other sizes would be about the same.

As for the calculator, I think what confuses people is that I made it to calculate for both square and circular fireboxes. The way the cells are laid out makes it confusing to some as to what numbers they need to use. Also, as you did, some people put the cooking chamber numbers in to the calculator and get huge numbers that donít make sense. Iíve been thinking of breaking the calculator down into two calculators for square and circular fireboxes. That should help clear up the confusion.

If you pm me I will give you my standard e-mail and you can send me the file you mention and I will try to answer your questions.
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paulhayes



Joined: 15 Aug 2009
Posts: 17

PostPosted: Sat Aug 15 09 1:56 pm    Post subject: Please HELP! what size? Reply with quote

Hello to all fellow chefs and bbquers. I am new to pit building and was wanting to know how to use the calculator I am starting my pit (cooker) with a 250 gallon barrel (tank) what would my fire box size, inlet tube (rectangle), and smoke stack (round) need to be I have played with the cal. and cannot figure out what I need to do all the help would be greatly apprecdiated.
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Tom C
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Joined: 21 Jul 2007
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Location: N. California

PostPosted: Sun Aug 16 09 4:18 pm    Post subject: Reply with quote

paulhayes,

I have been playing around with making the calculator easier to use by making one for round fireboxes and one for square. I will get them posted when I get a chance.

As for you smoker, you don't give the diameter of your tank but here is what I have come up with.

You have a 250 gallon tank. 1/3 of that volume is 83.3 gallons. That converts to about 19,251 cubic inches that you need for a firebox volume.

I'm assuming that you tank is about 30" dia. If you use 30" dia pipe for a round firebox, it will need to be about 27.25" long.

A square firebox could be any number of combinations of WxHxD as long as the cubic inches come out to the 19,251volume needed.

With a round firebox you will need an air inlet to total about 48 sq. in.
With a square firebox it needs to be about 57.25 sq. in.

For both types of boxes the opening to the cooking chamber needs to be about 154 sq.in.

If you were to use a 5" dia pipe for a smoke stack on the smoker it will need to be about 49" long.

I hope this help you out.
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paulhayes



Joined: 15 Aug 2009
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PostPosted: Mon Aug 17 09 11:29 am    Post subject: Reply with quote

man this helps out alot but a couple more questions can I use 2 stacks that are 24.5" each? how far down should the stack pretrude through the top of the cooker? or is the 49" from the outside of the cooker up? Very Happy
'
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paulhayes



Joined: 15 Aug 2009
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PostPosted: Mon Aug 17 09 12:37 pm    Post subject: Reply with quote

Tom C.

Man you seem to really know your stuff, I hate to keep bothering you but I am excited about my pit building and want it to work good. What do you think aboiut the Lang style cooker reverse draft with the firebox and stack at the same end? How about the conventional firebox at one end stacks at the other? and finally the firebox mounted on the reaer of the barrel running length wise with the cooker (simmilar to a rotisserie style but not a rotisserie) and the exhaust stacks on top of the cooker. I want a good cooker that is easy to control. I have all the material and things to complete the project andhave some local help from some metal fab shops, and a railcar company the is doing all of my welding and plasma work and they will heat the tank prior to working on it so that the metal looses all of its memory and the cuts will be clean with very little warpage if any?
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Tom C
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Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Tue Aug 18 09 2:59 pm    Post subject: Reply with quote

paulhayes,

No problem about asking questions I'll try to help as best I can.

1. yes you can use two stacks as long as you have the total volume you need for a good draft. You can mount them coming in from the top or from the side. I placed mine on the side at or a little below the cooking grate level.

2. All of the smoker types you mentioned work great! It comes down to what you want to build. There are some tough choices when it comes to what kind to build. I chose mine becaused it looked like something I could actuall pull off. Wink I was happy with how it came out.
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paulhayes



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PostPosted: Fri Aug 21 09 12:24 pm    Post subject: Reply with quote

Tom C.

I was figuring my firebox size and I can use a 26"X36" round box to get my needed size, but I have found a 20" X 48" but this will still be somewhat shy of the 19251 that is needed in a fire box, do you know what effects a smaller box has? I could make it longer but I have located a pipe that size in a 3/8" that will be given to me instead of the $300.00 tag on the 26"X36" piece. Also the 20" piece will fit better on the trailer that I have.


Thanks!!
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