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Science behind smokestack size?

cmayna

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Is that formula only for a certain type of smoker such as a charcoal one?  What about Electric and propane smokers?
 

cmayna

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Question:  Does type of smoker (charcoal, propare, electric, etc)  dictate different forumlas?
 

ccjammer

Newbie
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Joined Jul 23, 2014
ccjammer here,i have a 20 inch x 48 inch long cooker with a  18 x 20 square fire box offset

it has a 3 inch dia. x 30 inch long stack on the side top and was wanting to replace with a 4

inch dia. that is 4  foot long,is that sufficient enough or do I place it towards center of pit,any

.answers will be very appreciated. 
 

pootin pig

Newbie
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Joined Jan 13, 2016
Trying to determine exhaust stack size. I'm wanting to do dual stacks. I've taken an old pig cooker that is 60" longX30" deep, and 30" high. I built a firebox that is 24x24x30 with an opening that is 30x 51/4. The firebox is mounted on the lower back of the cooker and I have a plate inside of the cooking chamber to spread out the heat. I want to do dual stacks on the top at the rear corners. the only calculators I found give you single stack only. I'm thinking like 2- 3" stacks around 32" tall should do it. What do you think???????? Would that be the same as 1- 6' stack?
 

daveomak

Epic Pitmaster
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No... not the same....   actually exactly half the size needed....   4 - 3" stacks would be the same...  I would go with 2 - 5" stacks...
 

bitterroot mt

Newbie
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Joined Mar 30, 2010
I know this is a old thread but based on the 15%

and 1/3 theory

if my tank is 92 Long

it is 38 wide

My stack should be  6in wide and 31 Tall.

I am building a firebox from 2 55 gallon drums w with doors at either end like drum stoves.

23 wide 70  long

I realize it is a little undersized .... all I could scrape up.

.

2  6 inch inlets between the firebox and cook chamber .

Set up like a diamond plate Pit Mod.

Anyway.. Could I use   two   3 inch or 4 inch stacks  with dampers.on this and mabey a little shorter   say 24-26 inches tall

and be ok ..

MY thought is that it would hold in heat longer and  still let out the correct volume.... am I correct here?

Thanks
 

dave schiller

Meat Mopper
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Joined Apr 7, 2017
I used to heat my house with a wood burning stove and from all I read and learned, the draft effect of the chimney is caused by heated air being less dense (lighter) than cold air.  The heated air in the flue therefore rises, inducing (pulling) cooler air into and through the heating chamber.  Since the heated air rising up the flue is gradually cooled by contact with the flue, I guess it's possible that if the flue is too long, the heated air will drop to the temperature of the ambient air, thus eliminating the draft effect.

Conversely, if a fan is used to force air into the heating chamber, as with a BBQGuru or similar system, then it wouldn't matter if the flue gas is too cool to induce draft through the system.

My guess is that the optimum length for a chimney on a smoker will vary with the ambient air temperature.  That is, during hot summer days, longer flues can be used.  But on very cold winter days, a long flue may result in too much cooling and reduce or eliminate the draft effect.
 

Ron Burg

Newbie
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Joined Nov 18, 2018
Looking to do a vertical smoker.
50 high x 23 wide 18 inches deep.

Do I need 2 smaller stacks on each side...
1 larger one in back
Ranger uses no stack, on one model just open vent in bac k.

Thanks
 

anstissk

Fire Starter
74
15
Joined Apr 7, 2011
OK..... so I ran the numbers for a 48" x 20" CC and my calculator comes up with a 20" tall stack X 4" diameter...... I would make it 30" tall just because.... Pretty much what your 16" tall x 4" diameter...... Your engineers probably copied us.... HAHAHAHAHA...... our members make some darn good smokers....
Dave, so just because I am curious...I have seen on a few builds where the OP did the calculations in the tutorial and you mention that you would make the stack longer. In this example, you mentioned you would make it 10" longer just because....
Is there something driving that decision, do you like taller stacks in general? Just curious
 

daveomak

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Joined Nov 12, 2010
Natural draft requires volume in a stack to reduce friction and pressure differential to facilitate draft... Pressure differential can be from height of stack and temperature differential of gasses in the stack and ambient temperature.......
 

anstissk

Fire Starter
74
15
Joined Apr 7, 2011
Natural draft requires volume in a stack to reduce friction and pressure differential to facilitate draft... Pressure differential can be from height of stack and temperature differential of gasses in the stack and ambient temperature.......
Makes sense. So typically just adding some additional length as it most certainly will not hurt anything.
 

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