24" 3/8" wall pipe 45" smoker * now with some que view!

Discussion in 'Reverse Flow' started by kfd518, Nov 8, 2014.

  1. Looking to build a 45" smoker out of above mentioned pipe. Length as brought to me is 60". Attached bellow are rough draft drawings for box will be made from the 15" cut off all plate parts will be cut out of 1/4" steel except top of fire box which will be 1/2" plate. Top of warmer box will be the pipe cut out of the top of the fire box. Scale is 1 box:3". How high should RF plate be and what pitch if any end to end? Fire box I believe may be slightly under sized due to cutting the top of it off to make it flat is there any way to get around this? If I use a bit more wood I'll be alright, just don't want to reload every 45 min is all
  2. oldschoolbbq

    oldschoolbbq Smoking Guru OTBS Member

    Hey,that sounds cool , keep us posted and have fun with it . You'll have all the info. you need right here... the search engine at the top will be your best friend , and you;ll get to know our resident building Gurus well.

    Have fun and . . .
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Think about making the FB from 3/8" plate and having the smoker 60" long.... Much better having the FB square/rectangle....
  4. Using what I have available for the most part, 3/8" is expensive stuff. No scrap yards around here selling out of the yard anymore makes used not an option. 60" is much more smoker than I will ever need either. Right now I've got it figured to where all major parts needed will be coming out of one 4x8 X1/4" sheet and then have to buy Round stock and angle and strap for doors and grates… got it figured right now minus trailer at about $300-$350 budget
    Last edited: Nov 8, 2014
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    It appears you have used Feldon's calculator.... Over the years, the members on this forum have made some improvements to that calculator.. those improvements are reflected in the numbers below....The original calculator caused the FB to overheat and hot spots near it... the numbers below show a marked improvement in air flow, uniform temperatures and a reduction in fuel usage.... as reported by members making improvements to their smokers....

    23.25 ID x 45" length... 19,105 cubic inches CC
    FB volume should be about 6400 cubic inches... or larger... larger is better
    FB to CC inlet 19,105 x 0.004 = 76 square inches.. the same under the RF plate and the same at the end of the RF plate.... Those numbers are for good air/heat/smoke flow through the smoker....
    FB air inlets.... 19 square inches... 15" for the lower inlet and 4" for the upper air inlet... or somewhere near there.....
    Exhaust stack... 325 cubic inches... 5" ID stack 32" tall above the CC.... add more if you are extending it into the CC or to a plenum...

    Segment Height ED..... 5.5" = segment area 76.8"
    Chord AB = 19.76".... width of the RF plate

    .... The Calculator .....


    Last edited: Nov 8, 2014
  6. Thank you for that calculator I have been trying to find one to work the math.

    Just trying to clarify what is the reason behind the upper inlets? More complete burn of fuel gasses and better draft?
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Just trying to clarify what is the reason behind the upper inlets? More complete burn of fuel gasses and better draft?

    Yes...... you've got it...

    The upper air inlet moves the heat from the FB to the CC without adding air to the fire....

    The lower air inlet is used to adjust the heat for the cooking process.....

    It can be used to gently tweak the temps in the CC by adding cooler air or reducing it....

    If you make too big a fire, you can adjust stuff easily and still maintain good air flow.....

    Make sense ????
    Last edited: Nov 8, 2014
  8. Makes plenty of sense. Also one other question, what I have figured is roughly 6300 CI on fire box as designed curently which is about 98.5% of what you have recomended at 6400CI should this make much difference ? Just winding as the missing size equates to a little less than a 5" cube. What thermometers do you recomended? Would like one in CC & warmer door
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The CC will be OK.... bigger is better.... more room for ash.... Therms.... Tel Tru makes some good ones... adjustable also on some models... When installing therms, use a digital that's cabled to a probe to measure the temp on the cooking grate where the food is.... note the difference between that and the mounted dial therm.... that difference should be close to the same over the cooking range of the smoker and make a chart.....
  10. CC? Lost me there. Which measurement we're you referrimg to? Teltru is who I had looked hardest at so far… figuring on needing an ash pan in it to make it easier to run the thing. I do know while operating my wood stove in shop even as old and leaky as it is I get a pretty clean burn in it but someone else figure out the airflow in it, not me…and all metal between FB and CC removed so as to ensure the best flow possible correct?
  11. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I meant the FB @ 98.5% would be OK...
  12. Alright, just making sure. I appreciate your information And sharing your wisdom on a rookies build sir!
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Hey.... No problem..... some of the best smokers in the country are built by members of this forum.... Everyone wants you to have the best smoker in your town....
  14. Dave, something about the stack volume as listed being 325 is showing weird according to my math.
    3.14x2.5(2)… 3.14x6.25x32"=628 . Am I missing something in my math?
  15. lendecatural

    lendecatural Smoking Fanatic

    Your math is quite good, but you do need some length to get the heat "pulling" out of the exhaust so it is usually recommended to have a stack at least 30" in length. Since you need 325, you could use 4" pipe and still be good with a stack of 30+ inches in height.
  16. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Yes you are..... You are missing my "In my head" adjustment.... A 5" stack calculated out to being 15" tall.... soooo... that may be a little short... The stack still needs to be 325 cubic inches.... 19,105 cu. in. CC X 0.017 = 324.7 cu. in. exhaust stack...

    325 cu. in. / 0.7854 / 16 (4" stack Sq.) = A 4" stack 26" tall... (I would go 30")

    GOOD JOB catching that......

    I have stuff figured in my head and skip over a lot of it.... anyway..... 4" stack 30 inches above the Cook Chamber....

    I must have been checking something when that 15" tall stack number popped up and sent me on some road to fix it...
    I keep trying to do 6 things at one time.... when I know I get screwed up.... good thing you caught it and good thing I could find it....

    anyway, the 0.7854 number comes from 3.14159.... 1/4 of it... Check out r2 and d2... d2 is 4 times r2... so the equation NOW becomes.....
    d2 x [3.14159 / 4] (0.7854) = area

    If I screwed this up.... Let me know....
  17. I'm starting to second guess my math skills a bit but I recall equation for area being
    A=Pi *(r2)… volume equation as follows V=H*Pi* (r2)

    Was not aware that Pi could be changed in area and volume calculations only the change In measurement of the circle used, but it does come up correctly learn something new every day. Lol
    I do see what you are saying about the length and needing it to get the draw, was just afraid if I had it too long that it would draw the heat out of the gasses to quickly causing a cool and drop effect instead of heat rising draw effect. So my question now becomes would i be better suited to use 4" pipe or 5 inch, and should it be dead center in the arch of the pipe or set back slightly as I see many of them set?
    Last edited: Nov 11, 2014
  18. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I would use a 4" pipe.... the original calculator states a recommended length.... If you started by looking at Feldon's calculator, there was a descriptor in the exhaust stack section..... I have copied it below....

    Chimney Size
    Enter the diameter of your chimney pipe to find out how long it should be.
    • A chimney that is too short may produce insufficient draft (drawing of air). A chimney that is too long may cause the air to cool before it exits, reducing effective draft and worse, dripping of exhaust materials onto food!
    • Many horizontal smokers have an exhaust between 30-40 inches in length, but there is no hard and fast formula.
    • If you are building a horizontal smoker with a vertical cooking cabinet, realize that the cabinet partly acts as an exhaust, thus you may greatly shorten the chimney.

    As far as stack location...

  19. doug kiser

    doug kiser Fire Starter

    DaveOmak,don't know where to contact you? New to smart phones. Try to send pics. Cc is 26" by 50" by 3/8.fb is 22" dia.by 24 by 3/8 wall.Need to know the size the football cutout is.Which will determine how high the rf plate is.Thanks Mister Dave!
  20. Finally getting started on this build but the plans for it have changed quite a bit. Still 45" chamber. Came across another piece of 24" pipe 22" long for fire box. The extra 15" will be used when I want to cold smoke for sausage and jerky, completely sealed off from main cook chamber except one opening at the bottom for smoke to flavor when curing.

    Fire box welded on and door cut. Will add pics later.
    As stated…
    Last edited: Oct 13, 2015

Share This Page