# Chimney Question



## big country (Apr 21, 2010)

Hey Everyone,

I am almost done with my build, (sorry for not posting pics, but I will try in the near future). But here is the question that I have. The build consists of a 250 gallon propane tank and a 24"h x 30"w x 30"d firebox, I built this as a reverse flow smoker and I am not sure how far down inside the tank the chimney should go. I am not sure if I want it to go straight out of the end and then go vertical, or should I just cut a hole in the top of the tank and just go vertically with the chimney. If I just go vertically directly over the firebox how much space should I have between the two. I want it as close to the grill level as possible but I do not want to restrict the flow of smoke out of the chimney. BTW the chimney will be 6" diameter well casing. Any help would be great. Thanks in advance. Erik,


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## garyt (Apr 21, 2010)

I have a Lang, on mine the stack dosent go down to the grate level, it is flush with the top, I dont think you need the stack at grate level with the reverse flow design


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## garyt (Apr 21, 2010)

also Google "pit building calculator" for tips


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## big country (Apr 22, 2010)

Thanks for the information Gary, but I cannot get the calculator to load, I will have to try a different computer.


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## rickw (Apr 22, 2010)

Try  Here ...........


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## smokeon (Apr 22, 2010)

I too have a Lang, and can verify that the chimney doesn't go below the top of the chamber.

Here is one thing I've noticed though.  The themometer on the chamber consistently reads 50 degrees higher than the probe at the grate level when the damper is full open.  I can tighten that temp difference up by closing the damper some.  I've had it about 1/3 open and the two temps were pretty close.   

My theory is that by adjusting the damper, I can simulate the chimney extending into the chamber.  If the damper is full open, then the heat runs along the top of the chamber and out.  So the top where the Lang thermo is located is hotter, and the grate is cooler.  If the damper is closed, the heat backs up and the whole chamber warms.  So the two temps are closer together.


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## corn cob (Apr 22, 2010)

I understand your theory...the heat backs up (collects) in the cooking chamber and somewhat equalizes the two thermometers...The stale, acrid smoke, (ash, soot, etc.) also is backing up...and cooling...possibly creating an environment for creosote build up in your cooker and on your meat. 

Why is important for the two temperatures be close together? You know the Lang Thermometer is giving you a bogus reading as it relates to the cooking grate...Seems a better idea would be to ignore the Lang thermometer altogether, or just cook 50*(or whatever) higher knowing your cooking grate temperature is really 50* lower...Also, you could just remove the Lang Thermometer, plug the hole and use your remote thermometer ~~~ All of the competent cooks I have ever known say leave the smoke stack fully open at all times....Use the air intake to control the temperature ~~~ Anyway...Food for thought!

Fun!


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## big country (Apr 22, 2010)

Thank you Rick it loaded nicely that time. I appreciate the help everyone. Erik


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## lightfoot (Jul 4, 2010)

when i built mine, i brought the stack just flush with the top of the inside of the tank.  I went to the trouble of making a "slider" pipe, that fit inside the actual stack, that i could adjust up or down (inside the tank-all the way to the grate if needed) since i wasn't sure what the right spot would be.  After quite a few smokes, i found it worked best just to take out the slider and leave the exhaust out at the top of the tank.  My thermometers are mounted on each end of the tank (also a reverse flow), just a couple of inches above the grate-where the center of the food normally is. I figured that would give a more accurate reading of actual heat temp at food level, than at the top of the tank.  The fact that heat rises, just made sense to me that the top would be hotter than grate level.


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## tukson (Jul 4, 2010)

For what it is worth .... 3cents maybe....

I like the idea of full exhaust and keeping the chimney pipe as hot as possible to help with the draw during the complete smoke session.....

ok maybe 1cent...


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