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Top and Bottom Vents

edited 1:06PM in EggHead Forum
I picked up a Demo EGG last Saturday at the SoCal EGGFEST. I keep on learning about the EGG from here and the EGGFESTS. So now I am "playing" with the new EGG and there is going to be a learning curve on this EGG.

From what I understand, the Lower Vent is the Intake and the Upper Vent is the Exhaust. From Grandpas Grub diagrams on the openings of Lower and Upper Vents for certain Temperatures, the opening on the Lower Vent is about 1/4 of an inch and the Upper Vent is opened to get a specific Temp. By doing so, does that mean air is coming from the TOP ? Wouldn't be easier to open the bottom to get more air to raise the Temp as it would be to close the vent to lower the Temp. How does the Upper Vent work in relation to the Lower Vent ?

Any help in understanding all this would be helpful.




  • FidelFidel Posts: 10,172
    They work in harmony. Air goes in the bottom and comes out the top. Either one can restrict airflow. The amount in can be controlled by closing the bottom OR by closing the top - the volume of air inside the air won't change.

    You can hold 300 degree by opening the bottom about a half inch and removing the top completely OR by opening the bottom all the way and opening the petals on the daisy fully open.

    Basically the amount of air is controlled by the smallest opening either at the intake or the exhaust.
  • BotchBotch Posts: 6,360
    I'll have to look up that Grandpa's Grub thread (he's already helped me a couple of times in 3 weeks) as I'm kinda unsure which way to go, too.
    Live fast, die young, and leave a well-marbled corpse.  
    Ogden, Utard.  
  • Carolina QCarolina Q Posts: 13,020
    Unless I'm doing a 250° cook, I never use the cast iron DFMT. Top is always wide open The bottom vent does just fine all by itself. I'm told that works for 250° and below too, but haven't tried it.

    I hate it when I go to the kitchen for food and all I find are ingredients!


    Central Connecticut 

  • Grandpas GrubGrandpas Grub Posts: 14,226
    The picture post is a guide to get someone started with general settings.

    Heat rises. When the lump bed is stable it will draw air from anywhere it can find the available oxygen, and will pull from air through the lower vent. The heat going out will the upper vent. If the lump bed is blocked in the upper end you will see smoke exiting the egg through the lower vent which is a blockage - be cautious of flashback when opening the egg and flashback through the lower vent.

    Some time ago in another post Stike had some good comments about the lower vent and the DTMF. The heat of the egg is mostly being regulated by either the upper vent or lower vent.

    As the DFMT can change when the egg is opened or if it gets bumped somehow, I use the lower vent as my main control and use the DFMT as a fine adjustment. Probably in that case the DFMT is actually controlling the burn and not a combination of the two.

    I can control the eggs via the lower vent without the DFMT installed . I do find it hard to control the egg at temperatures below 225° without the DFMT.

    I can also control the cook temperature with the lower vent and screen wide open by using the DFMT.

    I am not sure if this really works, however, if I want less smoke flavor in the meat I will leave the DFMT completely off of the egg. If I want heavy smoke flavor I will leave the DFMT on and closed as much as possible to keep my cook temperature.

  • Judy MayberryJudy Mayberry Posts: 1,991
    Just a question from a non-tech head...does the amount of lump that is in the Egg have anything to do with the temperature?
    Judy in San Diego
  • stikestike Posts: 15,597
    this analogy hasn't caught on yet :laugh: , but think of it like a garden hose

    the lower vent is the faucet at the wall, the top vent is the end of the hose.

    either one can stop the flow, you can use both, or just one...
    ed egli avea del cul fatto trombetta -Dante
  • srq2625srq2625 Posts: 262
    On in the sense that more lump means air has a slightly harder time flowing through a large lump pile than it does a smaller lump pile. In large part, I think that's a technical, nit-picky consideration.

    Temperature in the egg is more a function of how much lump is actually burning and at what rate is it burning ... and that is a function of the amount of air (oxygen, actually) flowing across the lit charcoal.
  • ShedFarmShedFarm Posts: 499
    Thanks for the tip! I gave it a try last night, just using the bottom vent to control the temps with my medium. It actually made it easier for me to dial in 400 degrees and keep it there, with only one variable to change.

    I think I'm going to go this route for a while, and see where it takes me. I would love to be able to do everything but the low and slows, without having to fiddle with the DFMT.
    BJ (Powhatan, VA)
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