#11  
Old 01-22-2012, 04:38 PM
Serf
 
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Default Re: Help understanding air draw and venting?

I most definitely plan on having a vent landing area and chimney. I just don't care for the look of a big chimney flue sticking up from a beautiful oven housing. As such, I just wanna know how small/short I can make it.

Side firebox smoker? Now you're speaking my language! I have one too. That's what got me interested in WFOs, I was thinking back then about making a better smoker, a brick smoker. I stumbled onto this site and the budget has been destroyed ever since.
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  #12  
Old 01-22-2012, 05:48 PM
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Default Re: Help understanding air draw and venting?

There are tables to determine the optimal flue size VS stack height, but they are for fireplaces not ovens. The important factors for good draw are:

Smooth transition. The better shaped your transition from the entry to the stack, the better a given size will draw.

Flue shape. A 6" round flue is better than a square 8" flue, and a (clean) steel flue is better than a (clean) terra-cotta flue.

How you build your fire. You want a small fire putting out lots of heat to get the stack warmed up first, then it is game on.


If you do not want the chimney stack at the front of the oven, consider building a squirrel tail design.
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Old 01-22-2012, 06:54 PM
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Default Re: Help understanding air draw and venting?

Quote:
Originally Posted by Tscarborough View Post

How you build your fire. You want a small fire putting out lots of heat to get the stack warmed up first, then it is game on.
T,
That is as close as anyone on this sight has come to cosigning the "old folks method" of preheating a chimney/flu before lighting the fire
http://www.fornobravo.com/forum/9/fl...tml#post125619 (Flue has trouble drawing when it's windy.)
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  #14  
Old 01-22-2012, 07:02 PM
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Default Re: Help understanding air draw and venting?

Part of my job involves diagnosing issues with new fireplaces. At least 50% of the time it is simply a matter of how they build a fire.
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Old 01-22-2012, 09:06 PM
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Default Re: Help understanding air draw and venting?

Quote:
Flue shape. A 6" round flue is better than a square 8" flue, and a (clean) steel flue is better than a (clean) terra-cotta flue.
Tom- this is the first time I have heard of this. Does this primarily apply to fireplaces, or any word burning device? Is there a minimum length for this to be true?

John
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  #16  
Old 01-22-2012, 09:38 PM
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Default Re: Help understanding air draw and venting?

It applies to airflow no matter what the purpose. I have the information at work and will post the tables and charts tomorrow.
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Old 01-22-2012, 09:39 PM
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Default Re: Help understanding air draw and venting?

Quote:
Originally Posted by Gulf View Post
That is as close as anyone on this sight has come to cosigning the "old folks method" of preheating a chimney/flu before lighting the fire
Man I can just hear the banjos starting up.......
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  #18  
Old 01-23-2012, 05:49 AM
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Default Re: Help understanding air draw and venting?

Quote:
Originally Posted by Tscarborough View Post
It applies to airflow no matter what the purpose. I have the information at work and will post the tables and charts tomorrow.
The formula to calculate "q" (volume of air moved) uses the diameter of the flue and pi, so it's treating everything as a circle anyway. Then with the square flue, you probably have added air friction from the dead space in the corners.
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Old 01-23-2012, 01:21 PM
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Default Re: Help understanding air draw and venting?

Actually I believe q is based on the hydraulic diameter, which ends up being the diameter when it is a circle but is calculated via 4A/P where A is the cross sectional area and P is the perimeter. Hydraulic diameter essentially converts any shape to the round equivalent.
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  #20  
Old 01-23-2012, 01:31 PM
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Default Re: Help understanding air draw and venting?

That is the way it works. I thought I had the charts electronically but only have them on paper. The only thing that is not common sense is that square and rectangular flues are measured by outside diameter and round flues are measured by interior diameter. Don't ask me why.
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