Weird temp problem on new 160 gallon build!

Discussion in 'Reverse Flow' started by rikun, Sep 8, 2015.

  1. rikun

    rikun Fire Starter

    Hi there,

    I finally got my 160 gallon project somewhat finished. Well not finished, but it cooks :)

    However, there is a weird temp problem, the firebox end is considerably cooler than the far end! I though it's usually the other way around ;)

    All the openings have been made according to Feldon x 1.5 / Daveomak calculator, and I don't think I have any airflow issues.

    However my doors are very leaky currently (and I mean very), so I'm wondering if that could be the culprit? Maybe the hot air coming under the RF plate leaks out from the first door and cools down when it reaches the FB end. RF plate is a bit hotter on the FB end, I cleaned it and got most sizzle from that end.

    The tank is 78" long and 26" in diameter. Disappointingly it's only 1/8" thickness, but I don't think that's the problem.

    Otherwise it cooks great and I can fit more than 100 pounds in there at once :)

     
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The smoker must be air tight to work properly.... If it leaks air, you are in deep doo-doo.....
     
  3. Is the smoker set up level from end to end.  I had an issue with my pit this past weekend.  I cooked on 
    Saturday & after the cook cleaned up the smoker.  In order to help with the cleanup I raised the tongue end of the 

    smoker to facilitate drainage for cleaning.  When I cooked again on Monday I didn't initially return the smoker to dead

    level.  This small change in elevation was restricting flow making for a smoker that was running 30 degrees hotter

    than normal.  Once corrected the temps leveled out where they needed to be.  In short a very small change can cause

    a big effect.  The doors and leaks could well be the problem.  I would seal them up with gaskets or whatever method would

    work for you and see what change that makes. With a long smoker like yours airflow will be critical.
     
  4. rikun

    rikun Fire Starter

    Levelling doesn't matter, I have the same temp problem no matter if I raise, dip or level the tongue.

    I suspect the doors also, I'll have to report after I'll get new doors rolled. Long story short, I made the flanges too small to accept gaskets, so gotta get new doors rolled that fit on top of the tank.
     
  5. rikun

    rikun Fire Starter

    Hi there,

    I just got the doors pretty airtight, but the problem still persists.

    The lower rack near the FB is very cold, it runs at around 225F or less when the upper racks are in the +300F range.

    I know some difference should be expected since hot air rises, but the lower rack further away from FB is much closer to the upper racks.

    Currently I can't really cook anything on the rack closest to FB, it's just too cold when running decent temps on the other parts of the smoker.

    Any idea what could cause this? I'll get some more pics from the insides this week. And I'll do a biscuit test to verify everything.

    The smoker currently is not perfectly level in the other direction (some roll), could this affect the temperatures? The tongue is perfectly level, I checked it yesterday.

    How about making the end gap on RF plate smaller? Could that help?
     
  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Take pics of the FB..... door, air inlets.... any gaps.... It sounds like you have air leaks somewhere.... Doors on the CC.... FB not welded up tight.....
     
  7. rikun

    rikun Fire Starter

    I Might have a few really small pinholes in the FB. Like that small you can't see them and no smoke comes out. I'll go over the seams one more time with soap and compressed air.

    Cooking chamber is tight, I temporarily taped the doors 100% airtight with aluminium tape to test if the doors indeed were the culprit...

    Here are some pics. You can see what I mean by the cooker being on a roll angle. I'll put it on straight ground in a few days to test if the roll could affect the uneven temps. I don't see how, but then again I'm not a physicist :)

    The holes in the back are for temp probes, they fit pretty snug. Oh yeah I should clean my RF plate ;)

    Smoker is perfectly level on cooking chamber.


    Level on firebox also.


    Not level on roll axis, does it matter?


    Firebox, main intake on bottom, upper intake on door.


    RF plate end with grease drain.


    RF plate FB end.

     
  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Try building a bigger fire... a HUGE fire to get a good bed of coals... then the air adjustments will adjust temperature.. bottom for the fire, upper for moving heat through the smoker......
     
  9. rikun

    rikun Fire Starter

    That might work since I have really small coal bed at all times. I've built pretty big fire for big coal bed, but I can't maintain the coal bed during the cook.

    The coals disappear very fast and I can't throw enough splits to maintain it without getting my pit too hot, even if I reduce the intake air.

    I think I'll try using some charcoal to maintain my coal bed next time and see if the temps will even out.
     
  10. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member


    Then you have air leakage somewhere.... If you close the upper and lower air inlets to the Firebox, the fire should go out....
     
  11. rikun

    rikun Fire Starter

    Well yeah I guess it would go out if I _completely_ closed all the vents. Haven't really wanted to do that with burning straight wood, been afraid of creosote.

    I'll do a test cook with big coal bed, I think it could even out the temps a little bit better.
     
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    If the fire goes out, there will be no creosote.... but you will know if there is air leaking.....
     
  13. rikun

    rikun Fire Starter

    Got some more testing done, I used around 5 pounds of unlit lump and one chimney of lit lump on top. Then I tossed a few splits on top and let my smoker heat up to 500 F. I adjusted my intake almost closed (it's substantially oversized from Feldon) to get down to 300 F and the fire seemed to run a lot smoother now.

    The fire wasn't as fierce as before, before the fire was really ripping and I had so much draft there was a loud hum inside the cooking chamber. I also had some ash from the fire flying inside the cooking chamber. Temp control was much easier now, previously I had some serious temp spikes as I added splits and the splits burned out way too fast.

    The lump and coal bed still disappeared pretty fast, so I had to add more lump to keep a nice coal bed going.

    The temps were a lot more even, I think I had around 40 F difference between hottest and coldest spot. And now I even got the bottom right grate hotter than the top right!

    The fire went out almost immediately when I closed the intakes, so I guess leaks aren't a problem.

    So maybe my problem was fire management.

    Maybe I read too much into burning a small clean fire, so I burned only 1-2 splits with so much air rushing in they burned down to coals in less than 15 minutes. Also I was lacking smoke flavour, so maybe that'll correct itself too.

    Have to do a long cook to make sure I'm still burning clean fire and not getting bad smoke.
     
  14. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Thumbs Up
     
  15. rikun

    rikun Fire Starter

    Still having problems, I don't know why it ran more steady previously...

    The fire method was the same.

    On the far end away from FB top shelf I was running at almost 400 F when on the bottom shelf closest to FB at around 250 F.

    I did some testing with my IR thermometer and measured my baffle plate temps from various places:

    Right side closest to firebox: 392 F.

    Center: 302 F.

    Left side away from FB: 275 F.

    I also measured the temp of my cook chamber's outer surface from the top:

    Right side closest to firebox: 199 F.

    Center: 219 F.

    Left side away from FB: 251 F.

    I don't know if these help at all, but looks like the baffle plate sort of works and I'm losing quite a bit heat from left to right on the CC.

    I was still struggling with the fire management, first I built a large coal bed and then threw in a couple of splits at steady intervals.

    The coal bed went from big to nothing many times, I had to add full chimney of lump almost every time when adding splits to maintain a coal bed.

    It feels like the splits aren't producing nearly enough coals to keep the bed. And using more splits brings too much heat, in fact I had almost too much heat with just a coal bed without fire.

    Here are some pics of the fire, first is how I started my coal bed:


    Upper intake position when running at 300 F range.


    Lower (main intake) position at 300 F range.

     
  16. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    rikun.... afternoon..... sorry to be the bearer of bad news....


    Like these upper air inlets...

     
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    EASY FIX........


     
  18. rikun

    rikun Fire Starter

    Well not according to Ribwizzard, who at the time of my built I considered the pioneer of the upper air inlet..

    Here's a post from long time ago when I asked about the intakes: http://www.smokingmeatforums.com/t/157515/intake-styles

    I am aware that Ribwizzard has since built fireboxes with two rows of upper intakes, so having one up higher would probably offer additional control.

    I can easily add second intake higher, but I'm 99% positive it won't solve my uneven temps.

    I'm thinking it might just be the nature of the beast, since my CC is only about 5/32" thick steel. Too much heat might be escaping through the CC walls, thus not radiating properly except from the RF plate which is 1/4".
     
  19. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Well, looking at your door and lower air inlet, BOTH air inlets provide air to the fire... Not what you want.... There is no need to add air at 2 different locations.... The upper air inlet moves heat/smoke from the FB to the CC.... The lower air inlet provides air to the fire to control the temperature....

    I know, that is what Ribwizzard recommends...

    Did you read the tutorial on building a reverse flow smoker ?

    http://www.smokingmeatforums.com/t/...others-ready-to-use-rev5-6-19-15#post_1264161
     
  20. How far down into your CC does your Exhaust pipe extend.  If it does not extend down into the chamber far enough all your hot air may be escaping out the exhaust thus explaining the lower temps on the firebox end which normally is hotter if anything.  I put mine down into the cooking chamber just above my lower cooking grate. You could try adding some temporary vent to the end to see what difference that makes. Good luck, Weedeater
     

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