Flue extending beyond crown on a chimney


Why are so many chimneys built with the flue(so) that extend above the crown?
For Looks?
To improve the chimney draw? I would think the small increase in height would make little or no difference
To allow the chimney to meet code? I would think the chimney could just have been built at the correct height in the first place.
Sheldon
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Makes a world of difference

 I would think the chimney could just

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Sheldon wrote:

The peak acts like a wing if the wind blows in a certain direction and causes a downdraft into the chimney, something you don't want especially if you are burning wood.
--
Blattus Slafaly ? 3 :) 7/8

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Sheldon wrote:

AFAIK, the code requirement in most areas is that the flue must extend at least 2" above the crown. YMMV
Picture wind gliding across a sloped crown with no flue extension. You can almost imagine the wind sort of sealing the flue opening.
Now picture wind gliding across a sloped crown and hitting the wall of a 2" extension. The wind is forced upward instead of flowing across the opening.
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extension helps screw chimney cap on......... try to do it with " flush flue"
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snipped-for-privacy@yahoo.com wrote:

But is that why it's code?
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I cannot find anything on the web that indicates that the flue has to extend 2" beyond the crown.
The chimney has to be 3' beyond the portion of the roof where it emerges. The chimney also has to be 2' higher than anything that is within 10'.
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Sheldon wrote:

I found lot's of references to the flue being 2" above the crown but none of them cite specific code references, other than "Check your local code". This site says it the best, but I've included a few other references for your reading pleasure.
ftp://imgs.ebuild.com/woc/M930413.pdf
Make sure the flue liner extends at least 2 inches beyond the top of the chimney, but check local building codes for the requirements in your area. This extension permits attachment of a rain hood and keeps ice and snow that accumulates on the crown from dropping into the flue. To avoid excessive cooling and condensation, don’t project the flue liner more than 6 inches above the crown.
http://www.chimneylinerdepot.com/lander/articles/chimney-anatomy.asp
Most flue liners extend above the chimney crown at least two inches. In some chimneys the liner may extend higher than this depending on local building codes.
http://www.diychatroom.com/showthread.php?t970
The crown should slope away from the flue liner, the flue liner should protrude at least 4" from the crown and the joint between the flue liner and the cap should be sealed with a flexible joint sealer.
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Thanks
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In our area it must extend 4inches or more 6 is the norm
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The building code for my state does not specify that it must extend beyond the crown, unless the crown is considered an "enclosing wall". Even then there is no dimension is specified. Diagrams in the code do no specify it either.
Flue lining (installation): Flue liners shall extend from a point not less than eight inches (203 mm) below the lowest inlet or as otherwise required by 248 CMR or 527 CMR if applicable, or, in the case of fireplaces, from the top of the smoke chamber, to a point above the enclosing walls.
wrote:

In our area it must extend 4inches or more 6 is the norm
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