# Vent size?

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#### davea37

##### Fire Starter
Original poster
In another thread, I offered up a question which addressed the size of the VENT port needed for a given smoker.  Which now forces me to ask this question of those who design and build smokers if they see this post:  Is  there a "rule of thumb" for the opening size of an exhaust vent?  (I'm not building smokers, I'm just curious).

This question comes from an observation of my Masterbuilt 40", propane fired smoker which has a relatively small (in my opinion) exhaust vent.  That particular vent consists of 4, 3/4" wide x 3" long "slots" which are "baffled" by sliding a small plate over the opening, thus creating a way to open and close the vent damper.  It has VERY little open space when slid wide open but seems to work as intended..

The air coming into the box comes from the same hole as the burner on the bottom of the smoker box and that particular hole diameter is approximately 8" in diameter.  Lots of air can comes in that hole.  Seems more than enough to make the smoker function as intended.

Does the smoker work properly?  Yes.  I recently did a 10 # batch of polish sausage and a 5 # batch of breakfast pork links and both came out much better than I had anticipated being they were the first two batches of sausage I had ever made.  Smoking brisket, pork shoulders, chickens, turkeys and LOTS of ribs has been my lot but sausage was a "test run" to see if the wife and I wanted to do more.  (The simple answer is "yes") Pepperoni and Landjager will be next on the agenda in a few weeks).

Anyone care to opine?

Tks Earl.  That helps a lot.

Dave

Feldon's calculator has some problems.... The numbers generated are using the FB size and the FB/CC opening is too small... Input numbers so the FB is 100% of recommended then use all the numbers... multiply the FB/CC opening by 1.5 for an opening that should work better... Use the link below for an improved shape to the FB/CC opening that provides better heat and air flowl....
http://www.1728.org/circsect.htm

Dave,

Obviously you have done some research on this topic and for your input I am grateful.  Those folks that actually build  smokers probably don't go to the extent of calculating the vent sizes as you have suggested but build what they think will work.  (Do you think I'm off base with that comment?)

With my smoker, a Masterbuilt 40 propane fired unit, my observation (un-educated of course) looks as though the opening for the EXHAUST is a bit on the small side and I was pondering and considering adding a second exhaust or, removing the sliding vent system, attaching a "stack" and put in a stack damper which would open the hole size up.    I'm thinking that if I can have BETTER control over the exhaust, I believe I could control the overall heat much easier.   Am I wrong in my thinking?

A "Dave" here as well.

Dave,

Obviously you have done some research on this topic and for your input I am grateful.  Those folks that actually build  smokers probably don't go to the extent of calculating the vent sizes as you have suggested but build what they think will work.  (Do you think I'm off base with that comment?)

With my smoker, a Masterbuilt 40 propane fired unit, my observation (un-educated of course) looks as though the opening for the EXHAUST is a bit on the small side and I was pondering and considering adding a second exhaust or, removing the sliding vent system, attaching a "stack" and put in a stack damper which would open the hole size up.    I'm thinking that if I can have BETTER control over the exhaust, I believe I could control the overall heat much easier.   Am I wrong in my thinking?

A "Dave" here as well.

Control the intake air below the fire grate to control the heat output..... Then control the air through the smoker with a second air inlet above the fire grate... If the exhaust is too big or too tall, and sucks too much heat out of the smoker, then use a choke plate on top of the stack to compensate for too "large/big/tall" a smoke exhaust....

The folks that build smokers to sell "En Masse" build for looks .... "If it looks like Johnny Triggs smoker, someone will buy it....

~~"Control the intake air below the fire grate to control the heat output".....

"Then control the air through the smoker with a second air inlet above the fire grate"..

This could be done to improve the heat INSIDE the smoking chamber on the unit I have..

(By the way, this is why I started this thread in the first place thinking about improving heat control inside the smoke chamber)

" If the exhaust is too big or too tall, and sucks too much heat out of the smoker, then use a choke plate on top of the stack to compensate for too "large/big/tall" a smoke exhaust"....

This would definitely be an improvement on ANY smoker as you could actually have a much larger exhaust port if needed with the ability to reduce it down to "zero" if you so desired.

~~The folks that build smokers to sell "En Masse" build for looks .... "If it looks like Johnny Triggs smoker, someone will buy it....".....

You have a very good pointIMO, the smoker that works properly is the one I would prefer, no matter what the heck it looked like..

Thanks again Dave.  Good information for the wannabe smoker builder.

Dave

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