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# Yup, another one (updated, with pics)

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.

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Howdy heatmaker,

My drum has a dome lid with 4 1" holes for the exhaust.

But I have seen several that have just used the 2" bung hole for there exhaust.

helljack has build several drums, maybe he will chime in later tonight and offer his opinion based off what he has built.

My next drum will have a flat lid just so I can see the difference for my self.

I am updating my sig to include the link to my drum pics, which most of them are labled as to what I had done.

Tom

Well, using the formula for area of a circle (Area =Pi(Rsquared) or 3.14 x radius x radius, a single 2" exhaust gives you 3.14 square inches of exhaust area.

Using two 1.5" holes would give you 3.53 square inches of area.

Using two 1.25" holes would give you 2.45 square inches of area.

By way of comparison, my Weber lid has four 7/8" holes which equals 2.4 square inches of area.

So somewhere between 1.25 and 1.5 inches for each should have you in the ballpark.

Dave

The redkneck rule be, more exhaust then intake so it draws.  Nother words if ya got 3 3/4 inch pipe in the bottom ya got 2 1/4 inch (roughly) intake yer gonna wan't say 2 1/2 inch plus a exhaust, a bit more exhaust won't hurt nothin.  Be the nice thing bout a drum, it don't have ta be exact ta work like a dream!

Ol Dave there, he be a rite fine cipherer, I don't do them pie things, just adds up the wholes an see if an how big they need ta be!

you crack me up Trav haha i would like to hear how you talk in real life lol

Quote:
Originally Posted by travcoman45

The redkneck rule be, more exhaust then intake so it draws.  Nother words if ya got 3 3/4 inch pipe in the bottom ya got 2 1/4 inch (roughly) intake yer gonna wan't say 2 1/2 inch plus a exhaust, a bit more exhaust won't hurt nothin.  Be the nice thing bout a drum, it don't have ta be exact ta work like a dream!

Ol Dave there, he be a rite fine cipherer, I don't do them pie things, just adds up the wholes an see if an how big they need ta be!

Quote:
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.

go with the 2 inch you are wanting to do.

Thanks fellas. I just want to do it right the first time. Thanks alot helljack, I will check those sites out.

It's almost done. I loaded up the basket with about 10 lbs and let her rip. Got the temps up to 600*F+ to try and burn it out. It's a new drum, so I figured I didn't need a great big fire in it. I ended up scaming alot of parts from my offset because the UDS is going to replace it. I didn't go as fancy as I was first going to, but it still looks great! I will get some pics up soon. Thanks for the help!

Now there ya go! Welcome to the ugly club.  Looking forward to some smoked something soon.

Quote:

you crack me up Trav haha i would like to hear how you talk in real life lol

Quote:
Originally Posted by travcoman45

The redkneck rule be, more exhaust then intake so it draws.  Nother words if ya got 3 3/4 inch pipe in the bottom ya got 2 1/4 inch (roughly) intake yer gonna wan't say 2 1/2 inch plus a exhaust, a bit more exhaust won't hurt nothin.  Be the nice thing bout a drum, it don't have ta be exact ta work like a dream!

Ol Dave there, he be a rite fine cipherer, I don't do them pie things, just adds up the wholes an see if an how big they need ta be!

I don't think it would sound as good if travcoman didn't have such a cool avatar.

BTW.. I really like the pic you selected for your aratar.

Here it is. It's getting a season right now. Just trying to get a feel for it before i throw any meat on it. The stack and the lid handle are from my "retired" Brinkmann.

This is version 1.1.2. After a test run last night, I realized I couldn't get enough air flow through the estended 3/4 pipe. I already painted it so I couldn't return the parts for 1". So, I made another 1" throttle with stuff I had on hand. Also I put some casters I had on the bottom, and added a drain in the bottom and the Cleaver Brooks boiler emblem I had. Tell me what you think!

You can make the exhausts any size you like and then put the chrome stacks of any size around them as decoration. Just make sure the smaller stacks inside can't be seen and nobody will know the diff. I have a single 2" inlet that i made a damper for and I just open the factory damper on my dome lid.

I don't think drums are that finiky, Just be sure you can adjust the air going in..

I started it up today, again, to do another season/test. The temps ran allot better this time around. I had some un-expected company show up so I popped all the intakes open and did up some burgers, dogs and some chedderwurst. I tell you what, they came out great with a bit of hickory smoke flavor and I am some impressed with the way this rig runs. I will NEVER buy another El cheapo smoker again.

A bit a hillbilly comes out in day ta day conversation.  I ain't lost all my roots just yet an never plan on it.  Gettin ta be harder ta find folk who are proud a bein a hillbilly.  Wish I could get back ta the old ways more all the time.  Technology provin ta be a real pain in the backside as a lately.

Get some shine in me an the hillbilly will come out even more!

Quote:

Originally Posted by helljack6
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.

Well, actually, it DOES matter.  If your exhaust is too big, you'll get too much draw and have a hard time keeping temps down.  Even going from eight 1/2" holes to eight 1" holes makes a big difference in how the drum performs.

Like Trav said -- you want a bit more exhaust area than intake area.  That way if you want to cook something hot and have your intakes fully open, you always have positive airflow.

Dave

I have one 3" exhaust, two 3/4" and one 1" intake. I have found that it is hard to keep the fire going if I want my temps under 250. She runs well in the 260-275 range.

Quote:
Originally Posted by HeatMaker

I have one 3" exhaust, two 3/4" and one 1" intake. I have found that it is hard to keep the fire going if I want my temps under 250. She runs well in the 260-275 range.

One 3" exhaust has over twice the area as one 2" exhaust -- 3.14" square vs 7.07" square.  I'd say your exhaust is too big.   You could test it by partially covering the hole and see what it does to the temp.

Unless you're comfortable cooking there.  Each drum will have it's own personality and if you're happy with it, smoke on.

Dave

OK what is all of them pipes coming out of the bottom for???????

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