First UDS build - question on exhaust sizing

Discussion in 'UDS Builds' started by chipreibel, Jul 23, 2015.

  1. Hey, all. Long time lurker, new SMF member. I've finally received permission from my CFO (a.k.a. "Wife") to build a UDS.

    I was able to snag a food-grade drum with removable lid for free through a friend of mine. I will be picking it up from the sand blaster tomorrow and will begin the build this weekend.

    I drilled (2) intake holes (180* from each other) prior to having it sandblasted. My plan is to thread 1" close nipples into the intake holes and weld them into place. I will later install a 90* fitting and an 18 or 24" riser with a 1" ball valve on both intakes. From what I've read, most people use (3) 3/4" inlets (which equates to a total area of 1.33 square inches) and will cap off one or two inlets and regulate temperature with the remaining one or two inlets. With (2) 1" inlets, my total intake surface area is 1.57 square inches (both of which can be regulated with ball valves). Unless someone chimes in stating otherwise, I'm comfortable with my design/sizing for the inlet side.

    For the exhaust side, I went back and forth on how to handle it. My particular lid does not have any bungs - it is just a flat solid lid. Option "A" was to weld an exhaust into the lid itself and Option "B" was to weld an exhaust on the side of the barrel (just below the lip of the barrel). For three reasons, I decided to proceed with "Option "B": (1) I've read that the exhaust can "drip" water/soot from the warm humid air condensing on the sides of the exhaust, (2) welding an exhaust to the lid is sure to result is some warping (I'm a very competent welder, but I'm also a realist) and will make the lid heavier and more awkward to handle (3) I wanted to have the ability to add a longer "stack" to the exhaust (which is why I didn't want to stick a swivel grill-style vent in the lid).

    My question is this: Is a 2" exhaust (3.14 square inches) be sufficient or should I bump it up to a 3" exhaust (7.07 square inches)? Finding 2" black pipe is MUCH easier (and cheaper) than 3"...

    Thanks for your input!

    - Chip

    Don't worry - I've been lurking long enough to know that I need to post photos of my first smoke and Q.  [​IMG]
  2. Good grief I have no idea!!! I do however want to welcome you here and say hi!! If you go to roll call forum, people will be able to welcome you properly! This will give your post a little bump so hopefully someone who knows something about something will be able to answer your question! I've learned so much from these guys, you're gonna love it here!

  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Chip, morning..... I'm a fan of multiple drilled holes around the top of the sides of the barrel.... makes for uniform heat and smoke escapement.... Get some cork "corks" to plug the holes if you think it's necessary... I would go with 3/4 to 1" holes and 4-6 of them....

    Using a step drill makes drilling easy...
    Last edited: Jul 24, 2015
  4. See, chip? That's the guy who knows something about something I was telling you about! He's an encyclopedia and the crazy thing is he is not the only one around here!!!

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