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Heat Issues need help

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Hey everyone, I  recently built an offset smoker out of a 55 gallon drum and a side fire box out of 1/8" steel.  I have the chimmney down at grate level, i put in tuning plates about 4 inches below the grates, have a nice air inlet on my fire box that is a little lower than my charcoal grate, and i also had a baffle to push the heat down.  I put these in right off the bat before any burns.  I recently did a few practice burns and noticed i wasnt getting much above 175.  I took out the deflector baffle and that brought the hot side up to about 200 and then i took a tuning plate out that was closest to the fire box  and got it in the lower portion of my 220-250  target area.  My cold side still wont go much above 175, its like i cant quite get the heat transfer right.  I took all the tuning plates out because that just lowered my overall temp.  Im not sure if anyone can help but some input would be greatly appreciated.  Pics are on my profile in the album if you would like to see them. Thank you  
 

tom37

Master of the Pit
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SMF Premier Member
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Joined Sep 24, 2009
The first thing that I think I would try would be to run the numbers in the pit calc spread sheet. 

This will give you the minimum specs on your openings. Along with the sizing on the stack. 

To me the stack appears to be the problem, in my mind without the calc I would say that the stack is maybe a little on the small side for dia. And it looks pretty short. Combine this with the grate level, I would say thats the problem. 

Your cook chamber opening looks pretty decent but theres a chance that the air opening to the FB could also be a little on the small side. You could verify this by leaving the door open slightly to see if the heat builds. 

I dont have my link handy for the pit calc, so could someone pls post it.

Good Luck and pls let us know how this turns out. 
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Thanks for the quick reply, i did see the pit calc and i ran the numbers. It said at that pip dia. it would have to be like 5 foot long.   The smoke stack as of right now is two pipes one that is 2 and a quarter and the other is 2 inches so it slips inside one another.  Now are you saying my air vent is on the small side or the opening from the fb to the smoke chamber.  And ur also saying i should drop the grates some?
 

tom37

Master of the Pit
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I think the FB to cook chamber is probably pretty close. 

Maybe the opening to give air to the fire may be a little small. This one you can check by opening the door a little and see if it heats up a little more. 

Not sure on the grate height. Any chance you know anyone throwing away an old basket ball goal. Most of the time the pipe is 3 inch or so and may be just what you need. 3" would let you get way shorter on the height but still give you the vol you need. 

Also, with the stack being short, you may have troubles with the draft if its windy at all. Maybe turn the whole rig and see if that makes a difference.
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Alright thats what i was thinking, the calc said i need an air hole almost twice the size.  And as far the the chimney goes i put 3 inch dia in the calc and it said about 40 inches.  Now after looking at a lot of pits i have noticed peoples arent nearly that tall.  Can i make it shorter than what they are saying? Personally i was thinking maybe 20 in. outside of the pit.  I will try leaving the grates where they are and doing these other simple mods.  So im not sure if you can tell me this but by adding more volume to the chimney will this increase draw or what exactly? 
 

hexlobular

Smoke Blower
82
14
Joined Mar 25, 2011
I agree with Tom37 on the stack size being a little small; 3" would probably be a minimum diameter to use.  By the way it appears, I'd think it would have to be a lot higher to pull air very well.

Something else I was curious about; how long are you lettting your smoker heat up before attempting to balance the temps?  If you have thick tuning plates, they will take longer to get up to temp, but will hold it more constant once your heat is established.  You may also want to give it more time than you'd like to before making additional adjustments to the plates and dampers.  You can do some test smokes with a set amount of wood each time so you can see how long it takes for the starting temps to settle in, and then make small, controlled adjustments each time to dial it in where you want it.
 

tom37

Master of the Pit
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Its all about cubic inchs, 

on one of my smokers I started out with 4" stacks and it ran pretty ok. after a switch-a-roo I ended up going with an 8" stack that was even longer then twice the length of two 4" stacks. 

It runs way better now. 

Here is a shot of a drum rig I built and it runs pretty decent, 4" dia on the stack. 

This was built before I ever even heard of the pit calc. 



I think I got away with the short stack since I get the heat rising into the chamber more so since the FB is right under the cook chamber. 

You can always put a damper on a stack that is to large but other then a fan pointing at the firebox theres not much you can do when the stack is to small. 

You have the right idea tho, check out the easy mods first. And go from there.
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Thank you everyone, as soon as i get home this weekend from college i will cut a larger hole in the door and find a bigger pipe for the stack.  Hexlobular, i believe i let that pit set for 2 hours before i even touched it on the first burn.  The side closest to the box read about 175 and the side further away read about 190 or so. That burn was with lump charcoal and wood.  The tuning plates that i cut were 1/4" and i had a deflector plate that was just some 18 gauge.  Once i took that plate out, the side closest to the FB went up.  And I took out the tuning plate closest to the FB and it finally got up to about 220 on just charcoal. 
 

tom37

Master of the Pit
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Joined Sep 24, 2009
I have another question for ya,

I noticed it was ask in your other post and thought I would ask here as well in case you lost this thread LOL ,,, it happens. 

Anyways, is the fire grate as high as the top of the air inlet opening. 

Also, Is there any chance you can do a test burn with lump charcoal and a split to see if your troubles are from ash buildup on the fire grate. 

The lump will produce very little ash.
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Yes, well about half or so is above the inlet and the other half of the inlet is below the grates.  And actually my first test bun was strictly lump charcoal and wood lol.  So i know that its not ash build up.  Any other changes i shoud make? I think today i am going to raise that fire grate p a hair and i am also going to put in the new stack. I cut the hole larger last night in the fire box.  Would it help if i put a hole above the fire too or no?
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Hey yall, made some changes, 3.5 inch chimney.  Elevated the fire grate a little more and enlarged the air in hole.  The fire grate is just a little lower than the top of the air in hole.
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Just did a test burn on her, got right up to my target area with just lump charcoal and biquettes.  I threw a small log in there and it shot right up.  There is still a temp difference between the sides but at least its not 50 degrees anymore.
 

anstissk

Smoke Blower
142
82
Joined Apr 7, 2011
Whats a typical temp difference between the sides? and when i go to make some ribs easter weekend should i switch sides

halfway through?
 

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