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Vent advice (modifications for improvement)

post #1 of 16
Thread Starter 
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?)
post #2 of 16

I don't see a pic.

Happy smoken.

David

post #3 of 16
Thread Starter 

pic has been added.

 

and another of the overall smoker.

post #4 of 16
Thread Starter 

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. 

post #5 of 16
post #6 of 16
Thread Starter 

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

post #7 of 16
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....
post #8 of 16
Thread Starter 

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.

post #9 of 16
post #10 of 16
Thread Starter 

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?

post #11 of 16

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.

post #12 of 16

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. 

post #13 of 16
Quote:
Originally Posted by DaveOmak View Post


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.

post #14 of 16
Thread Starter 
Quote:
Originally Posted by tykenn28 View Post


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.

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.
post #15 of 16
Quote:
Originally Posted by busmania View Post

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?


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....
post #16 of 16

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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