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Oval flue performance?

 
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I am building an 8" batchbox.

I would like to use an existing chimney that has an oval shaped flue (see photo).
By my calculations the CSA of this oval is exactly the same as an 8" circular flue.

Question: How much will the oval shape of flue (instead of circular) affect performance?
IMG_0881.JPG
[Thumbnail for IMG_0881.JPG]
 
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You have a bit more friction on the sides.  The only way to know is to build i would say.
 
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Kelly Pridgen wrote:Question: How much will the oval shape of flue (instead of circular) affect performance?


Not much, I'll second Max in this. Most of the friction in square and rectangle shapes are from the corners. Yours is still quite good although the fast streaming, hot core of gases isn't round but stretched out a bit. As long as the chimney is straight up, smooth inside and the height is more than 16' I don't see any problems.
 
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