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Help with airflow

Garland210

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Joined Oct 20, 2020
Hello, folks! I just wanted to get your opinions/advice on whats going on with my airflow (or lack there of) . I just purchased an offset reverse flow smoker from a gentleman. I have fired it up twice but I cannot get the cooking chamber hot enough. I was able to get it up to 263 with the help of a fan. The cooking chamber is 20" diameter x 30" long. Fire box is 20" diameter x18" long. The exhaust vent is 3" diameter x about 30". I get nice fire inside the firebox but I just can't seem to get the heat into the cc. I am thinking a larger diameter exhaust. What do yall think?
 

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tag0401

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How are you reading chamber temps, dome or with that probe therm in the picture? Sometimes I have to crack the door on the side of the firebox.
 
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Garland210

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I am using a probe. I tried cracking the door open a bit, opening all the way and everything in between. I gives me a very small temperature rise.
 

JC in GB

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You could add a pit controller or possibly open up the exhaust stack. I would try to the open firebox first as tag0401 tag0401 suggested.

JC :emoji_cat:
 

daveomak

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The calculation works out for a 3" exhaust stack... BUT... due to the friction loss in the stack and that terrible 90 deg. elbow, it will not flow enough air to adequately pull air through the Fire Box...
I recommend a 4" exhaust stack, 35" above the Cook Chamber and weld it directly to the top of the Cook Chamber at the end near the Fire Box.... You can insert the stack into the CC 4-5" and cut the bottom of the stack at a 45- 60 deg. angle and have the angle toward the food racks for improved air flow.... like the RED stack in the drawing... BUT.. Keep the top of the stack 35" above the Cook Chamber....

Boykjo's smoker.jpg
....... Stack ideas 4.jpg
 

daveomak

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AND, you can add upper air inlets to move the heat OUT of the FB into the cook chamber WITHOUT adding air to your fuel.... I'd go with about 3 sq. in. of upper air inlet holes...

Make sure your Cook Chamber seals AIR TIGHT... air leaks are not your friend...

FB air flow diagram 2.jpg

Smoker Exh and Intakes 2.jpg

Smoker exh and int 3 Ahumadora.jpg
 

Garland210

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Thank you. If I cut the existing stack at the elbow and cap it, do you think that will be okay?
 

smokin peachey

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Yes what Dave said.
I wonder what the builder was thinking putting the stack on the side like that.
 

Garland210

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Joined Oct 20, 2020
Yes what Dave said.
I wonder what the builder was thinking putting the stack on the side like that.
I'm not sure. I didn't think anything about it. It is my first reverse flow. I just figured thats how it was supposed to be. I paid 780 for it. I thought it was a good deal.
 

1MoreFord

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Did I miss the area of the opening from the firebox to the cook chamber somewhere in the dimensions given?

If not then that needs to be checked too.
 

daveomak

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24" +.... The green area....

5f7 2.jpg
 

shannonc

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3 inch isn't enough. Definitely go 4 inch. If it were mine I would cut that stack off right at the chamber and weld a cover piece in. Relocate to the top like Dave said or fabricate a convection plenum like Aaron Franklin is doing on his patio smokers.
 

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