handling rain down the chimney

Discussion in 'Reverse Flow' started by stonemill, May 1, 2014.

  1. stonemill

    stonemill Newbie

    My self and a friend are building my first smoker and have been reading a lot of posts on the design issues. I am thankful for all of the free information out there, it has been helpful. I do have one question. My friend tells me of a method of keeping the rain water out of your cooking chamber. It is having the smaller pipe coming out with a second pipe with a larger diameter lapping the primary with room between the two. The theory is rain never falls straight down. With the secondary pipe above the initial chimney pipe being wider than the lower,the rain hits it and tracks down to the outside of the chimney. He used to work in industrial fabrication and says this is how all the factories do their chimneys. However he hasn't been able to locate the equations for figuring out lengths by diameters. Has anyone out there seen this and the equations. Thanks again for all the great info,,,, Keep calm and smoke on

  2. forluvofsmoke

    forluvofsmoke Smoking Guru OTBS Member

    I don't have much for hard numbers on this, but have seen the vent pipe configuration you described used extensively in the petroleum industry, though I'm not sure it was intended to prevent storm water intrusion, as it is used on gas flare-stacks...most likely it is intended to prevent flame-out during high-wind events, and/or, to improve oxidation of the fuel for a cleaner burn when a more extensive/complicated forced-air flare system is not used. I see the theory behind your intended use for this configuration, and it does make sense to me, as long as there is at least a light breeze during precipitation. What I've seen appears to be a 3:1 cap-pipe to vent-pipe diameter, and roughly a 4:1 on vertical, or, for every inch in diameter of cap pipe, it extends 4 inches vertically. Lastly, the cap overlap on the vent looks to be around 1/4 to 1/3 the length of the cap-pipe...for 24" tall cap, the vent is inserted 6-8". That's just based on my observations after 31 years working in the industry.

    An alternative to the above is a simple upright low-profile cone elevated over the vent stack which allows water to drop alongside the exterior of the pipe when there is not any wind during precipitation, though, with light to moderate wind, it is less effective...maybe consider using the two in combination if you desire protection from water intrusion under a wide variety of wind conditions.

    Good luck on your build and don't forget to post her maiden voyage!!!

  3. bob1961

    bob1961 Smoking Fanatic

    I'm going with a hinged flap on mine, with a leg mounted to underside of cap....it will hold open the rain cap like a stick, but since it will be attached to the rain cap it won't get lost....open it up to cook, when done and cooled off just hit the rain cap up a bit and the stick will unhook and close the rain cap....stick will be in the stack hanging from the rain cap when closed Thumbs Up ....
  4. I've always just used a tight sealing cap, figured if it was raining hard enough to mess up the cooking, it was my fault for poor planning!
  5. forluvofsmoke

    forluvofsmoke Smoking Guru OTBS Member

    ....BUT, many of us smoke in all weather conditions, so we do our best to mother nature-proof our rigs...[​IMG]

  6. Yep, good point..

    Wouldn't it just be easy to put a 45 at the top , like an exhaust stack on heavy eq , ?

    Could make it rotate, so when it's really poring and the winds blowing 60 mph gusts, just rotate the opening down wind so the rain won't go in.

    Or....just put the thing under a pop up canopy when the weather is iffy,
  7. forluvofsmoke

    forluvofsmoke Smoking Guru OTBS Member

    Not a bad idea...good idea, actually. That would work quite well with a centered swivel and a directional fin, if you didn't want to have to monitor wind direction changes. Even a full 90* elbow would work. Either one would need a fair amount of vertical run to get above anything close enough to cause turbulent air which may result in erratic partial rotation or improper direction, but yes, it's do-able. A slightly over-sized elbow over the pipe with a small amount of over-lap...good to go.

  8. Thinking just a slip on adaptor, that could be rotated to adjust for wind direction, removable for traveling or storage, might be a good solution for some.

  9. Have seen some use dryer vent elbows. They leave them off until needed, then just slip it on the chimney if/when bad weather comes. 
  10. brooksy

    brooksy Master of the Pit

    I personally use the canopy method. Only problem is the heat from my beast is right under the canopy and makes it thin in that spot.
  11. If it's a nice sliding fit it can be rotated as the wind changes direction too.
  12. stonemill

    stonemill Newbie

    Wow, I go away and build for a few days and I miss out on all of the advice. I ended up using the double stack and it is working great for keeping the water out of my smoker. The only problem is the rain water tracks down and splatters my smoker with soot. I was hoping to do a mossy oak break up, or something simillar for a paint job, but don't know if I want to be cleaning the outside every time it ranis. I took it for its for its first run last night and needed to rush the chicken along and couldn't get it above 250, maybe I didn't allow enough opening from the fire box to the cooking chamber, or maybe I did it perfect and just need to quit being in such a hurry. I would like to post a picture but I don't see where I can from here.

    Thanks again for all of the input and Keep calm and smoke on
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    What are the dimensions of the FB, CC, Stack, FB/CC opening and maybe we can help....
  14. stonemill

    stonemill Newbie

    sorry for the slow reply, I am still getting used to checking on feed back with forums. I cut out the baffle plate and made a new onne that sits a couple of inches higher than the original. My test run, once I had a good bed of caols and some fire, I was able to get the temp up to 400 and damper it back down to 220 in minutes. Going to do some smoking this weekend.
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Pictures of the smoker would be nice.....
  16. stonemill

    stonemill Newbie

    I will see if I can figure that out.
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Nice...... I like short, fat Cook Chambers........
  18. forluvofsmoke

    forluvofsmoke Smoking Guru OTBS Member

    I like it, too. In theory, it should give relatively small grate temp variations, being such a short run from the fire box and out the vent. Sweet rig!!! Just guessing here, gauging from the tire size, but it looks to be about a 3 large whole brisket main grate capacity, with some wiggle room. Add a sliding or static grate above that and toss in 8 or so pork butts. You've got a lot of smoker there, stonemill.

    Let us know how it cooks!!!

  19. stonemill

    stonemill Newbie

    I do have two grates in it. It is the first smoker build I have done. It is made out of a 125 pound propane tank, about 51 inches long and about a 36 in diamiter.
    I appreciate all the encouragement, I am a rookie for sure. I tried to follow all of the ideas from different threads on here as well as following the links to sites for the equations for figuring opening sizes ext. I am still learning the magic combination of fuel and venting to maintain temp, but I like fussing with it

  20. stonemill

    stonemill Newbie

    This is what I started with. I would like to get it painted in a Mossy Oak Break up pattern or something similar, Is there a good heat resistant paint or can they powder coat in multiple colors

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