Where to measure length when extending Highland stack? How much?

[Tallbald]

Several threads here found with a search discuss extending the stack several inches on an OK Joe Highland for a better draw and thus more air pulled in to the FB with better combustion as a result. I have a few ways I could accomplish this, but don't know where to measure for the increase. Stick a tape measure down the top of the factory stack and measure from bottom of factory welded elbow up to the damper plate?
The calculation formulas I have found just say "length of smoke stack". Several ways that could be measured I see. I'm not real sure either how long the stack should be for best performance. I'm thinking someone has already calculated this and would welcome a number.
Thanks as always.Don.

 

[jim2]

I don't think it is critical. In his book, AAron Franklin says that for small smokers a 4" to 6" diameter and 3' to 4' smoke stack is usually about right.

 

[Tallbald]

Oh. I'm stuck with the factory 3inch(?) diameter one on my Highland. Have to make do. Thanks for responding. Don

 

[Heart of Dixie]

Oh. I'm stuck with the factory 3inch(?) diameter one on my Highland. Have to make do. Thanks for responding. Don

I have an older (circa 2004) New Braunfels Oklahoma Joe Longhorn. I researched and read somewhere that you measure the distance outside of the CC. My "correct" length came to 34" so I added 11". It seems to draw pretty well whereas prior it struggled on very humid days. I pulled the calculation off of one of the online calculators. I hope this helps.

 

[Tallbald]

Thank you so very much. Don

 

[Heart of Dixie]

Update: Last week i converted my Oklahoma Joe stack from the factory 3" to a 4". The exit port on my smoker is 3.5" so I used a 4" to 3" reducer, trimmed flush on the CC side, a 4" elbow and a 24" piece of 4" vent pipe. Since it is for exhaust only I was not too concerned that the parts are galvanized. The pipe cost less than $14.00 The change improved the draft quality where i am no longer having major issues of smoke back-flowing out the fire box door or coming out the grease drain. I kept the elbow on the inside of the CC bringing the exhaust to grate level. With the new stack the tempertures inside the CC averaged from 1 or 2 degrees to maybe 10, ***side to side. I had to feed the small fire a 12" stick of seasoned oak every 30 to 45 minutes to keep the CC in the 250 to 260 degree range. I was quite pleased with the results and wish i had done it years ago.
*** Firebox baffle and 2, 4" wide tuning plates installed