New RF build calculations help

Discussion in 'Reverse Flow' started by tnhollerbach, Aug 7, 2015.

  1. I am starting a new build, I have the bug after my first budget build. So hopefully I can get a little more input on this one than the last. It was still a blast and produces some good eats.

    My idea is i want a center feed RF. I have seen the ones where the CC sits directly on top of the FB. I want to have a detached FB and pipe into the CC.

    What i am working with is an old 36x60 kerosene tank, a 16ft boat trailer and a FB that i will have built.

    I made up a rough sketch with some calculations that I used from feldons and Dave Omaks thread. I am not that confident in my mathematics so i just want to be sure and see if anyone may have some suggestions on the build. So if yall could take a look at the sketch and give some feedback that would be awesome!

    Thanks in advance!

  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  3. Dave, thanks for taking a look, is that a regulated air intake or just open holes?
  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Put slide dampers or what ever to control the air flow..
  5. smokejumper

    smokejumper Smoking Fanatic

    Hello TNHollerBach,

    What you have there is a DPP style pit.

    While Feldon's is more for a traditional offset, from what I have seen your numbers should be OK.

    Should breathe just fine.

    Will your RF plates angle up slightly from the center to the ends with grease drain in the middle?
  6. Dave, thanks for the input, what does the second intake accomplish?

    SJ, thank you!!!! I understand that feldons is for a traditional offset, I was just trying to get close and see what the feedback would be. I am not sure about the RF plate, should it be? that sounds like it would be the most logical option but I just do not know.  Like a V style plate? If so I do plan on having a drain, just wasn't sure about the placement? I also want to be able to put something in like a basket or something to be able to do direct cooking over charcoal if the need presents it self.
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The lower intakes control how much heat the fire puts out.... The upper intakes control the temp of the smoker by moving heat from the FB into the smoke or adding cool air to cool the smoker down..... Smokers need a fair amount of air to smoke properly... Also the upper air inlet adds secondary air to burn any creosote from the wood... The upper air inlet works best if directly across from the FB/CC opening....

    Last edited: Aug 7, 2015
  8. smokejumper

    smokejumper Smoking Fanatic

    You have a few options. You can angle the RF plate front to back, or left to right away from the center. You could even have it an inch or so higher in the center and lower on the ends. Think about equalizing the flow on both sides which will give even temps. Having the center the lowest point and a 0.5" to 1" rise to each end will be the easiest way to go. What ever you decide, the drain(s) should be at the lowest point on the RF plate(s).

    Any way you go is also compatible with using charcoal tray on top of the RF plate, so don't worry about that aspect. You will just need to design your charcoal tray to allow air to feed the charcoal fire.

    I hope this helps.
  9. Dave, That makes sense and I will plan on adding the upper air intake. Now that I think of it the last build I did I do have a hard time getting the smoke into the chamber in the beginning of a smoke. May have to modify that one as well.

    SJ, I will probably look at a plate that look similar to this, with a 2" or 3" hole for the drain. if I use a big enough drain I was thinking it could bouble as an air inlet when using charcoal?

    Also, a question. what is the standard measurements for the RF plate in relation to the bottom of the CC, the sides and to the bottom cooking surface.  Is there a calculator that will help with determining the position of the RF plate?

    I will get some pictures up of my tank that may help as well.

    Last edited: Aug 8, 2015
  10. smokejumper

    smokejumper Smoking Fanatic

    That looks good. I like the idea of having the drain double as the air inlet for charcoal.
    There is no calculator for this style of pit, but we can take some information from Feldon's and adapt it for your purposes.

    The area under the RF plate should be at least as big as Feldon's recommended FB-CC opening. I believe that is the only way a DPP style pit can get away with such a relatively small channel connecting the FB to the CC.

    Since your CC is 36" diameter, your RF plate should be placed at least 8" from the bottom of the tank at the center which will make it about 30" wide.

    A 1" rise to the ends will make it taper out to just over 31" wide at the ends.

    You want the same area at each end of the RF plated where the smoke makes the turn up into the top of the CC.

    At 31" wide, you need a space approximately 5.5" to the end of the CC. This will make each RF plate 24.5" long from the center.

    I would also suggest making the FB-CC opening 26" wide to match the width of your FB and increase the height to 6".

    The lowest cooking grate should be between 3" to 6" from the top of the RF plate. I like 5".

    This layout will give you lots of rack space and room to put in a charcoal tray as well.

    I hope this helps.
  11. This helps tremendously and I REALLY appreciate the feedback and Ideas. I understand that this is not a traditional build build but my vision is much greater than just the smoker and in order to make the vision work and maximize space on the trailer I had to look at this option.

    Here is the tank and trailer, the tank I got for FREE from a neighbor and the trailer was a great find. It is a 18ft boat trailer in great shape, I found it on CL for 100 bucks.

    hope to start working on the tank today.
    I originally had the design this way but changed it because I thought it was to big, I like this idea though. Also considering putting a damper between the FB and CC. your thoughts?
  12. Congrats on starting your new build, I'll be watching. Nothing like a good build.  The info Dave gave you on the upper vents on the FB door are in my opinion a must. I run a traditional RF and you can really control and fine tune your temp.

  13. smokejumper

    smokejumper Smoking Fanatic

    That is awesome. I love free, and $100 for that trailer is a sweet deal.
    Oh hell no.

    A damper between the FB and CC serves no useful purpose and will restrict flow even when fully open.

    The benefits people imagine they will get from a damper are better achieved with the secondary upper FB air inlet as Gary suggested.
  14. Thanks Gary, I never thought about the upper intake but I think that it will make a great difference. What style of air control do you have on your smoker?
    I was pleasantly surprised when I went to see it. The guy just needed it out of the yard. I'm always looking for a good deal!
    Lol point taken, I'm still just sorting through ideas. I don't plan on putting one in, instead I will go with the upper FB air inlet.  What type of inlets do you prefer?
  15. Here is what mine looks like

  16. Here is what you can do with proper dampening   This was for Kielbasa

  17. Gary, That's what I'm hoping for. How long did it take to get that temp up?
  18. Not getting a lot done at the moment due to the lack of metal working tools and the inability to weld but we are working on that!

    I do however have a quick couple questions that maybe someone can help with. I sent my firebox plan to the fabricator and he sent back the drawing below. I think i still looks good.

    One question i have though is, according to feldons i needed a 26x26x32 firebox. Is that outer dimension? Will the subtraction of the material thickness be a problem? Particularly on the smoke transfer chute?

    Question 2, on the smoke chute connecrion to the CC if you look at the drawing the chute is 26wx6Lx6d. Should i correct the bottom part of the chute to maybe 8L on just the bottom plate to compensate for the curve of the tank?

    Last edited: Aug 14, 2015
  19. smokejumper

    smokejumper Smoking Fanatic

    The material thickness dimension will not matter on the FB overall. It is close enough.

    The smoke transfer chute has less leeway since it is smaller and the material takes away a higher percentage of your area.

    Might want to increase the vertical dimension by the material thickness so that it is 6" high on the inside.
    Yes, that will make it much easier to fit to the tank.
  20. SJ, thanks for the quick response! These small details make me scratch my head. I appreciate the input very much!!

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