Need help with temp control. Please !

[hoosier53]

Recently built a reverse flow smoker from a 125 gallon tank. 67" long ( with semi-rounded end caps ), 24" side to side ( diameter ) , FB is 24X24X22. Smoker has reverse plate that runs from top of FB to within 4-5 inches of opposite end. 4" exhaust pipe that comes out in center of tank on FB end 3 " then turns straight up for an additional 42 ".Exhaust pipe has adjustable damper on top. I have 3 FB vent holes that are 3"wide X 4 1/2' tall. All fully adjustable.

Problem is that by the time I get vents and damper adjusted to get needed temp all adjustments are nearly closed and the fire dies out. otherwise the temp is through the roof ! I need help quick ! Thanks very much.

[Rodcrafter]

What do you have inside the FB is there a basket? I don't know what temperature you are shooting for but it may be that the bed on coals may not be sufficient for maintaining the fire. I would say build a good fire, allow the cooker itself to get up to temp. Then begin monitoring the fire, never adjusting the exhaust damper. Keeping a small fire going begin turning down the air intakes. But remember the cooker may have a happy temp other than the one you are trying to force it into. Only time will explain what that is. I will check the pit calc later when I get home

[Frank_Cox]

here's the numbers as I ran them through the pit calc. Looks like your firebox is 130%. I usualy stay between 105% to 110%. If the firebox size is too big you will have some swings in temp. they are they can be controlled but it takes some time to learn them.
Looks like the chimney could have been a little bigger. My numbers came up to 50" long with your firebox like it is.
your throat size should be 101" square. this would be something like 6" tall and 17" wide ish. most likely would be a trapezoid shape or half moon. Trapezoid would be bottom cord 8" top cord 17" total height 8". or something close to that.
everything else looks close. You could insulate the inside of the firebox and line it with 1/4" plate to get closer to the correct firbox size. line the walls and the door with 1" of insulation would get you down to 110%

[hoosier53]

50 Inches tall with the 4" stack ? Trapezoid , Is that the opening between FB and the pit itself ? What kind of insulation can I get that is 1" thick ? Where can it be purchased ? How do I apply it to inside of FB ? I appreciate your help very much !

[Frank_Cox]

I'll be insulating the firebox on my current build Click here : Mack later this week so you can see how I do it then. I use Roxul ( find it at any commercial insulation supplier)
The trapezoid is the throat opening.
for the pit to be balanced the stack would need to be 50" long. if you were to increase the diameter to 6" then it would make the stack shorter.

[mag1]

Hoosier53, I have about 1"x2'x20' left from my build. PM me and I can get you some specifics if you would be interesting in buying it. If might be a foot shorter, i have to check.

[noXcuse]

I'll be insulating the firebox on my current build Click here : Mack later this week so you can see how I do it then. I use Roxul ( find it at any commercial insulation supplier)
The trapezoid is the throat opening.
for the pit to be balanced the stack would need to be 50" long. if you were to increase the diameter to 6" then it would make the stack shorter.

I don't mean to hijack this thread, but I have a question about that Roxul. After reading your post, I did some research on it. That stuff looks awesome, and the local Lowes and Home Depot carry it. They sell it in 3" thick bats to fit inside walls. How well do you think it will work between the walls of a double walled firebox if I rip it in thirds? Basically making it 1" thick and stuffing it between two pieces of plate that are 1" apart. Do you think the R value would be good enough at 1" thick to prevent the outside of the firebox from getting too hot to touch?

[Frank_Cox]

The R value decreases when it is compressed. I use the rigid boards. I just updated the build with the insulation process I use.

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[Gizmo]

noXcuse check out the Eli thread in the RF department on here to see how I "ripped" that 3" roxul. It works pretty easy. I got a used up band saw blade from one of the local steel shops that they were going to throw out. A 4 foot hunk of that makes a great "insulation saw"

[noXcuse]

Thanks guys. Again, sorry to the OP for the thread hijack.