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    Airflow

    Meathead,
    i published this out in the public site, as well.

    Is there published science on the balance between using the inlet vent or the outlet damper on a classic offset smoker?

    It seems that, in theory, you are working with a closed cylinder with the air intake at one end and the air outlet at the other. A fire is built within the cylinder. The fire yields heat and smoke. Placing the fire near the inlet to be close to the fuel source makes sense.

    Opening or closing the inlet or the outlet will change the rate of fuel delivery to the fire. The only difference I can see would be at low flow rates. Having a wide open inlet would let more oxygen in just by diffusion if the fire is really close to the inlet. I just don’t know if it would make a significant difference. At high flow rates, I am not certain I see how it would make a difference how you regulate the flow. It seems to me that, in a relatively closed system, the intake must equal the outflow. Only if the flow gets so high that the inlet opening begins to have significant resistance to airflow would that make a possible difference.

    People talk about regulating the temp with one end and the smoke levels with the other. I can’t see how there can be a difference, as the production of smoke and heat are intricately intertwined.

    Just stuff I was pondering during my wait in line for a haircut!
    Last edited by Dr._Pat; June 9, 2018, 02:53 PM.

    #2
    This long presentation says one thing relevant to your observations: don't use the vents for temp control; use the size of the fire. But there's a lot of other interesting info in it. http://www.genuineideas.com/Assets/i...%20Blonder.pdf

    Comment


    • Henrik
      Henrik commented
      Editing a comment
      Word.

    • Troutman
      Troutman commented
      Editing a comment
      Thanks for resurrecting that, I hadn't seen that in quite a while. Also notice what he says about humidity. I have been a spritzing, water pan advocate, others, per a recent post, think its a waste of time. Blonder would seem to side with a more humid environment.

    • ClayJones
      ClayJones commented
      Editing a comment
      Yes thanks for that! I've been here reading through it. Humidity is one thing I have no clue about. Is there a way to gauge the humidity in your smoker, short of buying some sort of detector? I think its usually humid in mine naturally because I see condensation, but I really have no idea.

    #3
    When you say intricately intertwined are you making an arguement that as one increases so does the other.

    Comment


    • Dr._Pat
      Dr._Pat commented
      Editing a comment
      Yes, the more fuel (oxygen), the hotter the fire, all other variables being equal. The hotter the fire, the cleaner the smoke, right down to the point where you can’t see smoke at all. That is how I view the science of it, as I understand it.

    • Nate
      Nate commented
      Editing a comment
      Ok I misread your OP... thought for a minute you were going the other way with it.

    #4
    I use my exhaust damper to regulate the temps across the cook chamber. For instance when the fire's rip roaring and really good and hot, if I were to close my exhaust damper a little, it lowers the temperature on that side of the cook chamber, because it's slowing the airflow. I always leave the intake side fully open, because a hot fire makes the best smoke.. and I fully agree that the size of the fire is how you regulate your overall temp, not the intake vent. You always want your fire as hot as it can be, so to have a hot fire but not get temps too hot you need to just make the size of your wood/fuel smaller. For me for instance since I have a smaller backyard unit, the loaded Yoder Wichita, I use pieces that are about 10 inch long or so and quarter or 1/8 split. I think a mistake some folks make is using bonfire size pieces of firewood, and then closing their intake vent because their temps are too high.

    Comment


    • Steve R.
      Steve R. commented
      Editing a comment
      I was that guy, once upon a time. I soon realized that it's a lot better to keep bumping the temperature up instead of trying to cool it down. That's one reason I love cooking in really cold weather.

    #5
    I always advise my clients to leave the exhaust wide open and regulate the temp the best they can by using the size of the fire. Then they can trim the temp a little on the intake. When you try to regulate on the exhaust you will get incomplete combustion. Take a look at Franklin's or old style Texas brick pits. They leave the intake door wide open and have a large chimney for exit. The best quality smoke I find is smoke that is heavily diluted with hot air passing through the firebox.
    You want large airflow through the whole pit and there will be enough smoke mixed in with it to put on good flavor and a ring.

    My 2 cents.

    Comment


      #6
      This is another great learning post

      Comment


        #7
        On offsets the exhaust should be so tall it must be folded for transport; The exhaust must also be insulated along with the firebox. That'll suck some air on through.

        Comment


        • Ahumadora
          Ahumadora commented
          Editing a comment
          Most of my new pits have folding stacks for ease of storage and can pass through the toll booths here. You will find very few pits with firebox and stack insulated. Using heavy gauge steel is usually enough on the firebox. Most stack on larger offsets work good around the 36" length above the cook chamber. There are a lot of factors to take into account when designing a pit.

        • EdF
          EdF commented
          Editing a comment
          Ahumadora, you are a great source of information!

        #8
        Very good information. Thank you all for sharing.

        Comment


          #9
          Great question!

          Comment


            #10
            I love great airflow over a fire when smoking some meat.

            I remember learning that, for my use, the fuse method on my WSM allowed me to open the vents up from, say 10% on the bottom, to 30%, and still have about the same cooking temp. The result? Better tasting barbecue and prettier smoke ring!

            That led me to my stickburner style cooking, from which I have not departed.

            I'm not sure if intake or exhaust make a lot of difference - just haven't tested specifics. I know that on the huge 1,000 gallon style Texas pits, you want a fast airflow to keep temps even across the pit, and the big and tall stack allow that draft to rocket through there. I say amen to that! (I bought a 1,000 gallon pit and can't wait to build my own.)

            On my Jambo, I set the intake vent when I picked it up from them, and have not moved it since (ok, maybe I adjusted some at the beginning, now that I think about it). I will adjust the exhaust damper to restrict airflow if I put on fresh wood and the temp spikes more than I like. My basic setup is wide open, however, and with my standard fire size, the temp gauge is 275-320, with the grate temp 40 degrees below that.

            On my pit Myron Mixon, we're wide open at all times. Fuel size and fire are the only variable - just the way I like it!
            Last edited by PaulstheRibList; June 12, 2018, 09:31 PM.

            Comment


            • Henrik
              Henrik commented
              Editing a comment
              Yep, that's how I roll too. Airflow is king.

            • PaulstheRibList
              PaulstheRibList commented
              Editing a comment
              Go @Henrik!!

            • JeffJ
              JeffJ commented
              Editing a comment
              With my 14.5 WSM I only light 10 coals (Soo's Donut) and start with the bottom vents about 3/4 open and the top vent fully open. Temps will hold in the 230-270 range with this set up as long as the pan has water in it. Once the water evaporates temps will spike quickly but can be brought back under control by closing the top vent most of the way.

            #11
            Hey folks! I love how every question I have always has a thread here for it!

            I've had my Lang for maybe 9 months now and have gotten pretty good at regulating temp with the intake dampers. Now I have enough experience to understand the hot fire, clear smoke dynamic and am trying to get that down.

            My issue is, even with my vents all the way open my smoke is pretty visible for a long time. I can wait that out on the initial heatup, but when I need to add fuel later, isn't there going to be white smoke every time? Do you all preburn your logs? If so, how do you go about doing that exactly? Thanks!

            Comment


            • ClayJones
              ClayJones commented
              Editing a comment
              Thank's y'all! I've been building fires far too big. Heating logs up in the firebox would have been tricky using my newb technique... but building smaller fires is exactly what I'm working on as per the advice above in the thread so I think I can make this work!

              Give it a lot of air
              Regulate temp by limiting fuel
              Smaller splits
              Get em hot and ready to burn

              It's nice having so many mentors

            • ClayJones
              ClayJones commented
              Editing a comment
              Trying this out Friday on some dry-aged ribeyes I picked up yesterday, and then on a few St. Louis racks on Saturday. Big weekend. Will post pics if they come out alright! (Will slink away like nothing happened if they don't.)

            • ClayJones
              ClayJones commented
              Editing a comment
              So, I did all of this at my cookout this past weekend (smaller, cleaner fire and using cherry wood) and made the best ribs I have so far! I got a number of "these are the best I've ever had" comments which are always nice

              Thanks again gang!

            #12
            This is a very good thread. But it mainly addresses cooking in large offset cookers. For most of us backyard warriors; however, the physics are still the same. Take a WSM smoker. I have mine (along with a lot of others here) rigged up with a temperature controller and fan. The fire is regulated by passing air over the charcoal thus igniting combustion then shutting down when a certain temperature is read at the top of the smoker. Thus air movement becomes the first variable, which is certainly key to keeping the fire burning clean.

            After that it becomes the size of the fire itself. We've had numerous posts where folks complain that they can't control the temps on their WSM, either can't get them hot enough or can't seem to cool them down. I would say that 90% of the time it's not so much about the venting and air flow but the size of the fire. A 22" WSM can hold nearly an entire bag of charcoal, which lit will produce a 500* fire in a WSM in a matter of minutes. That's why, especially for low and slow, we use the minion method or the snake method so that the fire SIZE remains relatively small BUT with air management gets as intense as it needs to in order to produce a clean fire.

            I'm going to side with those that control the second variable, which is controlling the size of the fire instead of worrying as much about air flow management. That's actually my 3 cents worth, 2 cents ended at paragraph #2.

            Comment


              #13
              Huskee - Mind blowing. I have cooked in the Yoder Durango by intake only forever! I am noticing a 125 degree difference between right cook chamber temp, and the vertical chamber temp. Do you think I should crack the exhaust damper to get a more even spread? I never even thought to touch it (though it makes sense, as I cook in the BGE by top damper only, and rarely don't have the bottom wide open).

              On the wood side, I use the miter saw and chop about 6" split sections, and add maybe 2 or 3 chunks an hour in a long cook.

              Good go, just when I thought I was on level ground!!!

              Comment


              • Huskee
                Huskee commented
                Editing a comment
                Lol! Yeah, give the exhaust-wide-open a try. Hard to say the exact dynamics having the vertical chamber which I obviously don't have. But I suspect it'll even things out better. Report back!

              • PaynTrain
                PaynTrain commented
                Editing a comment
                Will do Huskee. Not this weekend, i will be in Cincinnati, but the next!! Will have 8 pork bellies to smoke, and moving them around a little less would be awesome!

              #14
              OK, so I've got the KBQ, which more or less takes care of the airflow with its fans. But I also have a BGE, and find that a different kind of beast in terms of fire management. It always seemed that small airflow was what was needed to manage temps. Still had to get it to the point where smoke hits the right quality. So last year I got a smobot. It controls the temps by adjusting the top vent. And it is virtually the same as doing it manually. So, I'm not sure what to say. I guess there's a convection effect going on in a kamado, that leads to a different approach.

              Comment

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