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Conflicting wishes for flue, erhmm maybe…

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  • Conflicting wishes for flue, erhmm maybe…

    I have a 32inch diameter low dome oven in my outdoor kitchen, i love it.

    But i have a few issues, the kit(casted dome) came with a short and small 4 inch diameter flue and china cap. More smoke out the door than out the flue at startup. Thats After curing proces and burning dry hardwood.
    i need a tall chimney to let the smoke clear my neighbours roof…

    i Can up the size to 6inches diameter but im stück with the 4 inc opening in the cast. Is This a problem?

    currently testing with a 4inch diameter 11 feet extention, seems to get the smoke clear of my neighbour as Long as i dont put on the flue cap, with flue cap on it obviously dont have the opwards pressure and it seems like the smoke is bunching up trying to get out and instead of dispersing it seems to want the smoke Clouds to go Down though my neightbours garden…

    Flue with better draw= means upsizing diameter, but guessing the sideeffect Will be less speed in the smoke exiting the flue?
    is there a cap design that restricts upwards flow less than a normal china cap?

    best regards


  • #2
    A 4” flue is definitely inadequate for a 32” oven, you need a 6” one. My ovens are only 21” and work well with a 5” flue. Area for a 4” = 12.5 sq in
    5” = 20 sq in
    6” = 28 sq in

    Making the flue taller does increase the draw but the effect is far more powerful by increasing the diameter and therefore the cross sectional area.
    There is another type of cap called an anti downdraft cap, but I doubt it will reduce constriction. You could try extending the legs on the China hat to make it taller.
    Really the better option would be to replace the 4” pipe with a 6” one and attack the entry to it with a diamond blade to improve flow. You will still have a restriction at the pipe entry but the extra draw from the larger diameter pipe should be adequate to overcome it. It will act like a venturi at that point with smoke accelerating there. You should find the extra height is not required, which also eliminates the need for stays to stabilise the extra height.

    Click image for larger version

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    Last edited by david s; 12-30-2022, 04:00 PM.
    Kindled with zeal and fired with passion.


    • #3
      Hello david and thx for the Quick reply and the illustration, its appriciated.

      Will start with extending High of cap, then on to anglegrinder… not much room inside the mouth though. I need to buy a less ugly flue anyway, so i might as Well go up to 6 inches. I expect to still need about same height so that the smoke still clears neightbour roof.

      Have a happy new year.