Need some help with my revese flow smoker

Discussion in 'Reverse Flow' started by miket, Sep 22, 2011.

  1. miket

    miket Newbie

    Hi,

    I built a reverse flow smoker - loosely based on the lang 36.

    Only made the drum 18" diameter and 36" long
    Firebox is 14.6" x 14.6" x 14.6"

    The question comes with the baffle plate - that is a touch higher than what I wanted, so the flow area underneath the baffle is a bit bigger than what the xls calc sheet calls for although I made the restriction at the end, where the baffle ends - very close to the correct value.

    The entry into the firebox is as large as the area under the baffle plate (quite a bit bigger than what the xls sheet calls for).

    Would it be better to decrease the hole from the firebox to the recommended size, or is it OK to have that too big and have the baffle plate end be the restriction ?

    Thanks
    Mike
     
  2. sunman76

    sunman76 Master of the Pit

    [​IMG]  good question I think it would be fine,  It should still have the same flow.  Don't know is it will do anything to change the heat though.
     
  3. hdflame

    hdflame Meat Mopper

    You didn't say if it was finished or not??  I'd just try it as is and see how  it works.  Let's see some pictures!  [​IMG]
     
  4. miket

    miket Newbie

    Ok, made some measurement and did some calcs.

    The xls spreadsheet calls for a firebox to cooker opening area of 24.74 sq inch

    What I actually have is 35.54 sq inch

    And the area at the end of the reverse flow plate to the end if the drum is 28.28 sq inch

    I am struggling to get enough heat in the system and it is real heavy on fuel :-(

    What is the recommendation - reduce the firebox opening ?
     
  5. What size is the air intake into the firebox?
     
  6. miket

    miket Newbie

    Finished - tested it - it works OK, temp from one side to the other is about 5 deg F difference, but really struggling to keep the temp up, and using allot of fuel :-(

    Some pics :)

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  7. sqwib

    sqwib Smoking Guru OTBS Member

    I would love to take a jab at this but really need to see some pics.
     
  8. miket

    miket Newbie

    Sheet calls for 9.28 sq inch

    Made the inlet 14 sq inch - seeing that they are adjustable I thought that some extra would not hurt :)

    I have posted some pics, but that is held for moderation - so should be up soon.
     
  9. sunman76

    sunman76 Master of the Pit

    This , and what is your smoker made out of ?  thinner mat'l does not seem to hold heat as well, but should be fine at 225 what temps are you going for?
     
  10. miket

    miket Newbie

    Hi,

    Firebox is 0.2"

    Rest of smoker is 0.12"

    Reverse flow plate is 0.08"

    One the test run I was doing some ribs and a pork but at 250 - and it took some work keeping it there.

    Fuel - I started with brickets but switched to lump after a while - was easier with the lump.

    Pics are on its way, but post is being moderated.
     
  11. miket

    miket Newbie

    here is the xls file i used for the calcs

    chimney inside diameter is 2.84" and is 24.41" long

    [​IMG]

    [​IMG]
     
  12. theoldman

    theoldman Fire Starter

    Wher can I download this calculator?
     
  13. sqwib

    sqwib Smoking Guru OTBS Member

    Mike the only thing I can see being a problem is inadequate intake/exhaust.

    Next burn do me a favor and raise your firebox grate above the intake, so the air comes from underneath the fuel.

    I am pretty sure your intake is undersized.

    Is your reverse flow plate on an angle, if so try angling the exit end up at level or higher than the firebox end.

    Are you running your exhaust full open, give me a couple more pics of that exhaust, it may be undersized as well.

    Although your calc calls for under 3" diameter for exhaust I would suggest 4" diameter.

    But I really believe the problem is your Intake.
     
  14. miket

    miket Newbie


    Hi, thanks for the assistance.

    No the plate is level

    The picture only shows one intake - there is another one exactly like that on the other side as well.

    Would it help if I make the firebox exit a touch smaller - more into line with the spec sheet - restrict it at the top - that way the reverse flow plate ends up being higher than the firebox exit ?

    Something like this :

    [​IMG]

    From some quick calcs I need to reduce the firebox opening by 0.8" at the top - would that be feasible ?

    Would the bigger exhaust not make the system even more fuel hungry ?
     
  15. miket

    miket Newbie

    One more question on the exhaust/chimney.

    I see every body always advises to keep the chimney wide open - so is a damper even required - or can I just skip that and go straight through chimney.

    With the 4" chimney you advised - what length should I make it then ?

    Thanks

    Mike
     
  16. miket

    miket Newbie


    I took some measurements and did some calc there is two intake wheels like the one in the pic - area for each wheel is 7.9 sq inch - so the total intake is 15.8.
     
  17. sunman76

    sunman76 Master of the Pit

    [​IMG]  when your cooking do you have flames coming out below the grate?
     
  18. miket

    miket Newbie


    Nope
     
  19. sqwib

    sqwib Smoking Guru OTBS Member






    [​IMG]

    [​IMG]

    For now I would just raise the fire grate above the intakes and do a test burn, take the least invasive approach first, just prop up with something, just be careful if using cement products as they may explode or shatter.

    [​IMG]
     
  20. I agree with SQUIB. Raise the grate above the holes. I don't think your fire is getting as hot as it should be. Low efficiency means more wood less heat. What you want is less wood more heat.
     

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