Vent advice (modifications for improvement)

Discussion in 'Reverse Flow' started by busmania, May 12, 2015.

  1. busmania

    busmania Smoke Blower

    I built a reverse flow smoker a month or so ago.  It works pretty good but I have a feeling it needs better venting for the fire. Can anyone offer some thoughts?  Also, could I add a vent to the opposite side of the firebox and vent from both sides?

    specs
    33 gallon tank
    16 x 14 x 14 firebox
    30" opening from firebox to CC.  same for the end of the RF plate area.
    2.75" inner diameter exhaust which is 24-28" in length (currently, I have it adjustable by stacking a 4" pipe on top of the existing exhaust).

    pic
    The lower vent is about 8" square and the top is about 2" square.  The lower vent is even with the fire grate (could this be my problem?)
     
    Last edited: May 12, 2015
  2. I don't see a pic.

    Happy smoken.

    David
     
  3. busmania

    busmania Smoke Blower

    pic has been added.

    and another of the overall smoker.

     
    Last edited: May 12, 2015
  4. busmania

    busmania Smoke Blower

    Let me explain a little bit about why I think the venting needs help.

    The smoker seems to draw fine from the chimney.  I cannot get the temp to stay around 250-275 unless I have a lot of wood in it.  However, if I have a lot of wood and charcoal in the FB, the fire seems to want to choke out and not burn cleanly.  Also, only the side where the vent is seems to burn "good".  The opposite side of the FB burns but not as "good" I suppose.  This is why I am wondering if it is OK to add a vent to the other side of the fb so there are vents on both sides. 
     
    Last edited: May 12, 2015
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  6. busmania

    busmania Smoke Blower

    Thanks Dave.  I did use that tutorial and built everything per that spec. Could the problem be simply that my lower vent is in line with the fire box grate?  Should my lower vent be under the fire instead of over it?  Same with my upper vent, should it be at the very top of the FB?  I put my upper vent about 2 inches from the top of the box.

    Here is the build.

    http://www.smokingmeatforums.com/t/181548/my-first-build-help-me-please-reverse-flow
     
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Maybe try raising the fire grate a couple inches..... also, the 90 degree elbow, in the exhaust, may be restricting the exhaust flow.... the elbow is a pretty good place for friction loss.... Also, are the doors air tight.... that could hinder the draw....
     
  8. busmania

    busmania Smoke Blower

    I was thinking about modifying that elbow.  Maybe Ill start with that and open it up where it goes into the CC and eliminate the 90 degree elbow. 

    The firebox is very well sealed.  the CC could be sealed better and is not perfect but it is close.  I am going to make a silicone gasket...one of these days.

    Ill try raising the fire grate an inch and see if that helps.  it is a good starting point, although space inside my fb comes at a premium.
     
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

     
  10. busmania

    busmania Smoke Blower

    Thanks Dave.  I originally did the exhaust off the side thinking it would save room inside the CC for food (it onlya 33 gallon tank).  However, after using it, I am no longer concerned with the amount of cooking space.  Am I better off just relocating the exhaust to exit the top?
     
  11. smokejumper

    smokejumper Smoking Fanatic

    Yes, it sounds to me like you'll get the most bang for your buck by either raising your grate to above the air inlet, or lowering the air inlet on the door.

    Raising the fire grate temporarily would be a good test. I would raise it more than one inch though. Get it fully above the air inlet.
     
  12. lendecatural

    lendecatural Smoking Fanatic

    I would do more of his alternate stack sketch but much closer to the right edge, of the dome line. It should be easier to do, you already have the bevel cut on the stack. Cut it at your 90, trim the stub on the tank, patch, then cut the oval in the dome and slip in the pipe. It shouldn't take too long, at least faster than building a plenum; however, a plenum would mean you could cover up the previous hole by making it bigger in the plenum if that makes sense. 
     
  13. tykenn28

    tykenn28 Fire Starter

    Sorry busmania, not trying to hijack your thread but this is somewhat related. I noticed while calculating for my smoker build, and agin on your picture that it says 36" +/-. Does that just mean it needs to be at least 36" above the CC? Even if the calculator calls for less? Just curious.
     
  14. busmania

    busmania Smoke Blower

    No problem. I struggled with that too on my build. The calc called for only 24" chimney. I ended up going w 29", then cut it to 24", but now I'm back to using the part I cut off to get it back to 29". The 36" is just a "rule of thumb" as I understand it. The draw on mine seems fine at both lengths.

    O, and yes, the calculated length starts at the top of the CC.
     
    Last edited: May 13, 2015
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member


    The plenum seems to work very well..... Unrestricted flow... Takes up no space.... and you only have to build it once and use it forever....
     
  16. tykenn28

    tykenn28 Fire Starter

    IC. My smoker is requires between 38-39" so it'll be more than 36" but I've just been curious about that and when I saw it again today on your thread I figured I'd ask.
     

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