How many intakes are needed? How aobut exhausts?

Discussion in 'UDS Builds' started by inkjunkie, Feb 23, 2015.

  1. inkjunkie

    inkjunkie Master of the Pit

    Have 8 3/4" pipe flanges,4 30" 3/4" black pipes, 8 3/4" nipples, 4 12" 3/4" black pipes, 4 ball valves and 8 or 9 3/4" elbows.....

    Plan is to just use the UDS for low and slow stuff.......

    Seeing as how I have 4 drums I very well may put a second one together just to use as a cold smoking chamber....
  2. dirtsailor2003

    dirtsailor2003 Smoking Guru OTBS Member

    I have built 2 UDS's. On both I put (3) 1" intakes with valves. Low and slow no problem, hot and fast no problem.
  3. inkjunkie

    inkjunkie Master of the Pit

    How many & what diameter exhausts?
  4. dirtsailor2003

    dirtsailor2003 Smoking Guru OTBS Member

    With both if mine I used the bungs that are in the lid for exhausts. Both of mine had a 2" and a 1" plug in the lid for a total of three inches. I unscrew the plugs when smoking and leave them open during the entire smoke. Since I store my drum outside I i screw the plugs back in when I'm done.
  5. inkjunkie

    inkjunkie Master of the Pit

    The lids we have are all solid. Wondering if 3 3/4" stacks would be enough? Also wondering if placement of the stacks matters? Can only imagine that it does...but that type thought processing is way above my pay grade so....
  6. As above, I would have thought this is ample.

    I plan on running 2x 3/4" valves and a 1" cap. Cap will be removed for getting temperature up, then put on when up to temp. Ball valves to control temp after that. 2x 3/4" or 1" should be ample airflow for low and slow, or hot and fast I'd have though.

    How far open do you have your 3 valves at ~225°F, dirtsailor2003?
  7. timberjet

    timberjet Master of the Pit

    Put the stack as close to one edge as possible. That way condensation won't drip on your meat. I use the stock lid like case does. Works great. 3 inch is big enough and I'm sure 3.5 would be fine if that's what you have for pipe.
  8. timberjet

    timberjet Master of the Pit

    In case you care, I have 3 3/4 nipples and 1 3/4 ball valve. Hot and fast or low and slow no problem. I could have got away with 2 nipples as I never have needed to use the 3rd one.
  9. timberjet

    timberjet Master of the Pit

    You only truly need one valve.
    Last edited: Feb 24, 2015
  10. dirtsailor2003

    dirtsailor2003 Smoking Guru OTBS Member

    Some of that depends on the ambient temp out doors. Perfect conditions 50-60 degrees out. Two closed one 1/4-1/2 open. 32-40 degrees windy rainy snowy two capped one full open, directed away from wind.
  11. timberjet

    timberjet Master of the Pit

    Yep, that's what I do this time of year.
  12. Thanks. This confirms 2x 3/4" valves will be ample for my drum. Where I live, the average temperature during winter is 61°F (day) / 46°F (night) and during summer is 84°F (day) / 62°F (night), with heatwaves regularly up to 108°F.
  13. inkjunkie

    inkjunkie Master of the Pit

    I need to be more careful when I type....only have 3/4" stuff. Was visiting a neighbor earlier today and was telling him about my upcoming project. He had some 1" flanges/elbows/close nipples/elbows/short pipes and plugs....basically everything I will need if (3) 1 inch stacks will be enough....
  14. inkjunkie

    inkjunkie Master of the Pit

    This is on the intake side, correct?
  15. c farmer

    c farmer Smoking Guru Staff Member Moderator OTBS Member SMF Premier Member

    (3) 1 in exhaust stacks isnt enough.

    I had (4) 3/4 inch for exhaust and the drum didnt work right.

    Now I have (8) 3/4 inch ones. Works much better.
  16. inkjunkie

    inkjunkie Master of the Pit

    Hmmm.....perhaps I should go visit my buddy that runs a NAPA and see if I could not barter a piece of 4" exhaust pipe and just weld it to the lid?

    Have a question after reading timberjets comment about placement.....need to get up and exercise think of how to word it correctly lol....
  17. Exhaust:

    The Weber lid has 4 each 3/4" Holes. That is Only 1.77 Sq Inches of Exhaust. The Weber lid works OK.

    The  2" Bung is 3.14 Sq Inches, which also works just fine.

    The Big Pappa UDS Kit has a Rotary style Exhaust with 8 each 3/4" holes 3.54 Sq Inches. It also works just fine.


    I have also seen builds with 2 each 2" Dual Exhaust Pipes 6.28 Sq Inches, which also seems to work fine. I would not get any bigger than this. This is probably double what you really need for exhaust.

    I believe as long as you have a little more Exhaust size than Intake size it will work fine.


    From all of my research it looks like 3 each 3/4" Vents will work fine. I like 4 better.

    I think most could get by with only 1 each 3/4 Full Flow Ball Valve. Leave 1 cap off, and fine tune with the One Ball Valve should work fine.  Again I have 2 ball valves.

    The Big Pappa Kit has a pair of sliding Intakes with 4 each 3/4" holes each. WAY more air than is needed for a Low and Slow cook. The Big Pappa UDS is set up to Grill also, so it needs more Intake Air for Grilling Temperatures. Using the Big Pappa Air Intake you need to only open it up 50% for Start Up.

    If you are going with a Flat Lid with NO Bungs, I would get the Big Pappa Exhaust Vent for $17.

    If you have a 2" bung add a 4 - 6 inch stack to it.

    For the Air Intake I would put in 4 each 3/4" vents. Cap 3, and a Ball Valve on the 4th.

    No expert, but that is what I would do.

    Last edited: Feb 24, 2015
  18. inkjunkie

    inkjunkie Master of the Pit

    Seen on another site someplace that folks mentioned drilling the holes on the side of the drum instead of the lid....supposedly keeps the rain out while smoking and allows for more even heating....and avoids the potential of drips form the exhaust....hmmmm....
  19. inkjunkie

    inkjunkie Master of the Pit

    Now I am beyond confused. The view from my side of the street....
    that when going low and slow you have a wide open exhaust and control the temperature with the intake side, correct? Which is exactly what people claim is done with a BGE. Tried this with our BGE today. Had the top wide open. Bottom vent open about .500". Temperature slowly climber to almost 350*. Shut bottom vent completely. Temp dropped to 330* and held steady. Only way to get temperature to drop was to throttle back the exhaust. Went from about a 4 inch or so exhaust to 1/8". Was then able to control the temperature with the bottom.
    Can someone please explain to me why a 3-4" exhaust is needed on a UDS? With my experiment on the BGE today I don't see how low and slow will be possible with that big of an exhaust....controlling on the intake side alone just doesn't seem to work...
  20. c farmer

    c farmer Smoking Guru Staff Member Moderator OTBS Member SMF Premier Member

    Your BGE is ceramic isn't it?

    That get hot and acts like a heat sink.

    That's my opinion anyway. Maybe I am wrong.

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