Originally Posted by HeatMaker
I just picked up an open head drum with a lid, brand new for free! I've looked around alot and gotten some ideas, but I have a question.
What size should the exhaust be?
I wanna make this thing look cool, and was gonna do dual stacks like a big rig. I was going to use 2" exhaust pipe and weld them to the cover, sizing the holes accordingly of course.
Any input would be good, thanks.
Personally, and this is just me speaking and how I do things, do whatever suits your fancy. As long as it:
a. cooks the food
b. can maintain cooking temperatures with little to no effort
c. does pretty much what you want to use it for
Who cares how big the exhaust is.
Now, the scientific side of me says go over to barbecuebible.com, check out the chargriller family thread and search for the exhaust calculator that someone built over there. Given the overall cooking surface area, it'll tell you how big and how tall your exhaust needs to be for the draft pull effect to be adequate on your smoker. A quick ref is if your cooking area is 22" round in diameter, then your exhaust should be 2/3 of that tall. Now, while this is meant moreso for sidebox/offset smokers, I've adapted this theory to several of my UDS within my fleet and i've never had a problem.
I would go even further to say, that having the appropriate amount of draft pull increases the air intake efficiency which allows me to operate low and slow with ONLY one air intake open all the time. I've never had to have more than one air intake open to maintain 210-240 temps and my exhaust is actually quite tall for my flagship UDS smoker (about 24" tall). And the best part about it is i'm using the standard 2" bung as the exhaust. YMMV so I recommend just giving it a try.
Now, i can't remember exactly who did it, but one of the brethren over at bbq-brethren.com did a single stack exhause about the diameter of a coffee can, ring locked a vaccum exhaust hose to it and used the hose to port exhaust a good 4 foot away from his UDS all together, says he's never had a problem maintaining temps or anything, go figure.
What it boils down to based on that, is it's not really going to matter HOW BIG your exhaust is, as long as you have one and it works for YOU because it's you that's going to be cooking on it, not someone else. Hope this helps.