Backyard 20 gallon RF. 1st build - Advice on too LARGE of Firebox

Discussion in 'Reverse Flow' started by mike dula, Apr 19, 2016.

  1. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Mike, morning....  You are absolutely correct...  My mistake...  I looked at the original numbers I put together and did NOT even think about how bad I screwed up with the decimal.....

    I love it when you folks take the time to point out my errors....   Shows you are into the build, pay attention to detail and double and triple checking the numbers..  Great job !!!!

    Time for me to start double and triple checking stuff...     Dave
  2. mike dula

    mike dula Newbie

    Shew...that would have been a big mess up. Glad I'm still worries Dave! Your math has gotten countless folks into smoking without screwing up the dimensions. Again, it's priceless info that most should be grateful for.

    I still need wheels, shelf, and paint. But I think tonight I will fire it up for a test run to see how it holds temps. I'm excited.
    Last edited: May 3, 2016
  3. Mike, you will still have to enlarge your lower intakes a little, 1 1/2 inch dia hole = 1.767 sq in. required sq in =4.6 sq in 80% of that equels  3.68 sq inches, your 2  1 1/2 inch lower holes only gives you 3.53 sq inches, 20% of 4.6 for the upper came out to .92 sq inches needed, so the 1 1/2 upper at 1.767 is fine, but the 2 lowers added are undersized. It's better to be over than undersized. Just figure out how much to square off the lower holes to be at or over the required 3.68 sq.inches needed, cutting out the piece between the lower circles to make one lower oval opening looks like it would give you enough sq inches.

    Last edited: May 3, 2016
  4. mike dula

    mike dula Newbie

    I think your right Hawg. I Fired it up tonight (so stoked). Works great! totally pleased. But this is my fist go around with a side flow...or really any smoker. 

    I learned a few things. 

    1. I took a while to get up to temp. Got up to 200 and would not go past...I cracked the door and temps went up because the firebox ignited. I had very little fuel to begin with. I filled the chimney started with charcoal and dumped it in, then threw in a couple of sticks, around 2" diameter size. I decided it needed more fuel so I pushed the fire back towards the chamber more and added a few small chunks of wood the a decent size log. With the door cracked, I had an inferno...closed it up and temps we're HOT. Closed off one of the lower 1.5" holes and cooled down pretty well...left it alone, and temps settled to about 200 again. Throughout the night I can keep it at 225/250 with all holes open but one, which I left half cracked. So, about 3 hours in, and the large log red hot, the fire box is blazing, but temps in chamber are around 225-250

    Its responding to the inlets changes well, but with all 3 open I'd expect it to get in the 300's fairly easily. Point is, it does act like it could use a little more air. 

    As far as even temps from left to right, the left gauge is always consistently 25 degrees cooler than the right gauge. That far left gauge is right at the end of the RF plate...I tried to keep the temp gauges as close to the cooking grate as I could. 

    2. Dumping hot coals from the chimney started on that tray is dangerous. They fell off the sides loading an end loader is difficult and I need some sort of tray under i. It needs some work.

    Overall. I cant wait to seaons it, and put some meat in the chamber this weekend. I just have a lot to learn to keep the temps right. How much fuel it needs, adjusting the inlets etc. I can easily square out the lower hole.

    Here are some of it in action tonight shortly after lighting it. 

    Last edited: May 3, 2016
  5. Always nice to see a new toy work!!!!

  6. Looks awesome!! Would be very happy with that  [​IMG]

    Want to do me a shipping quote to Australia for it? Haha
  7. mike dula

    mike dula Newbie

    Well. Its copper lol. I wanted a different color. Its VHT copper and ultra flame red vht on the cap of the fire box. Still neds more paint  for the legs and I need to get the wood cut and stained.

    So, with the larger opening up front, I was still having a hard time getting it to temp, like around an hour to get it to 225. Even then, It will stay real low, say around 200-225. But if I want to get it to 250 its a challenge without opening the door and letting the wood just turn to flame. Soon as the door is closed it cools back to the 200-225's If for a reason I want to regulate it and get it to the upper 200's I have to leave the door opened. Is it possible I need more fuel?

    I smoked some bacon on it last night and thin strips of sirloin For jerky. Turned out okay. Dave, being that my stack is at 32" with a 3" dia pipe, could it be too long / short causing the cc to not get up to temp? You mentioned 32 - 36"

    Last edited: May 8, 2016
  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I was reading where the FB was BLAZING and the CC was 225-250....   That is symptomatic of very poor air flow through the smoker...   How close is the RF plate to the end of the CC.....    Seal the CC door and the FB door and any place else there may be air leakage.....   Air leaking is your worst enemy.....   Does the exhaust stack stick down inside the plenum at all or is it flush with the top of the plenum.....

    If everything is perfect, cut out more steel between the FB and CC to enlarge that area....

    The FB fire getting hotter when the door is open is a dead give away to poor air flow through the smoker......
  9. mike dula

    mike dula Newbie

    Thanks Dave. I left 3.85" from the end of the RF plate to the end of the CC.  The door leaks but not bad. I can seal it better thought with a latch. The exhaust is flush with the plenum. 

    I wonder if the long firebox is causing a lot of friction and slowing the air flow down, of the end of the RF plate needs to be shorter. Everything was to spec but the FB to CC opening which I opened up a bit for a better rf plate seal. 

    Dave. I'll tackle any air leaks first. The FB is well sealed. The door could seal better. And the only other place I see would be the pipe out of the CC for the drain valve. See if that helps, at this point its going to be very hard to get into the CC/FB opening to enlarge it without cutting the welds and removing the RF plate. Otherwise I can shorten the plate..

    Any other tests I can do to try and locate the restriction?
    Last edited: May 9, 2016
  10. mike dula

    mike dula Newbie

    Okay heres an update. The measurements look fine to me. I measured about 20 times. I think my smoker is fine. One restriction I found was the hole cut in the side of the tank where the collector is welded on. There was some metal in that openining, a lip, I was able to take out to the welds/

    So...I did another test run last night. I think its simple. My smoke is "streaming" out of the top of the pipe, judging how the smoke has a nice velocity leaving the pipe, visually the flow of smoke looks good. It doesnt peter out of the top of the stock, a solid nice column of light smoke is evenly flowing out of the top. Its moving air. I sealed the door by wedging a board against it, forcing it more closed. very little smoke is leaking out of this smoker. 

    Im new to these smokers, is it user error? Do I just need more fuel / heat?

    I "think" I just need more fuel. Here is what I did

    1. preheated a chimney starter of charcoal. 

    2. Once hot, dumped it into the smoker. 

    3. Then threw in an unsplit small 2.5" stick and closed the door. Opened vents all the way.

    4. Took about 30 minutes, but it got to 200 then stopped climbing. 

    5. Tried craking the door a little...didnt make a ton of difference. The stick ignited. Temps rose to about 250. Closed the door. 

    6. Had to go in for dinner / get kiddo in bed. Decided F'it and threw in a larger split and another smaller stick, push the coals a bit more towards the CC. More or less trying to fill the chamber. Went inside. 

    7. About an hour later, checked on smoker. It was around 350.

    8 . Closed it off a little. Temps started to lower. 

    Is it possible it needs more fuel? For this size chamber do I need to load the tray with coal and dump the chimney of coal on top along with wood?

    Thanks all
    Last edited: May 10, 2016
  11. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Fill the fire box with coals and splits....  Get them burning very good...   When you see you have coals, add more splits and close down the air inlets....   leave the upper about 1/2 open....  close the lower about 1/4 open......     check later to see what's happening....  the bed of coals is exactly what you need and the smoker needs to be preheated.....  don't skimp on the wood.....
  12. mike dula

    mike dula Newbie

    Thank you again Dave. Will do. We had storms roll into North Texas tonight so I couldn't get it fired up. I rolled it in the garage to keep rain off her. I'll do exactly this and report back soon as we have good weather. 
    Last edited: May 10, 2016
  13. mike dula

    mike dula Newbie

    Actually. Ive been treating it like a weber kettle. Thow in the hot coals, close the lid, watch temps rise. With this one ive been throwing coals in, a split, then shutting the door...I think before the smoker has a chance to pre-heat. 
  14. mike dula

    mike dula Newbie

    I'm happy to say this issue was user error. The cooker is working flawlessly...Its just a learning curve. 

    Last night I loaded it up tray to top with coals and splits. Left all doors open for a bit and let the RF plate get nice and hot. Then I closed the FB lid, opened all vent fully, and closed the chamber. Temps had no problem getting to 300. Waited for the TBS and loaded up some sirloin strips for jerky. The valve is collecting grease, but next build its crucial to get that V in the RF plate. I have fat collecting outside the drain groove. 

    I closed the top 1/2 and lower one 1/4 and it slowly went down to 225. 

    If the temps dipped close to 200, I could open the bottom one full and the temps would take no time climbing back up. The fire never got too hot, and it took some playing with the intakes to keep it steady but no doubt it responded to the inlet changes. 

    I simply just didnt have enough fuel in it. 

    Super happy now. Cant wait to really figure out its personality. LOVE MY LITTLE CREATION!

    Thanks to Daves math, literally anyone can build an efficient cooker. 
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Glad it worked as it was supposed to....   Got any pics ???
  16. mike dula

    mike dula Newbie

    No pics of last night, was pretty dark as I didnt get it going till late. Pulled the jerky off this morning, thew it in a zip lock and headed to work. This weekend if the rain stays away I'll be doing a brisket.

    Did I mention I bought an infrared gun? Most of the time the chamber cap / hottest temps we're 450-500. After the hickory really burned down, the top of the CC got up to 650, at this time I had both inlets about halfway closed and was still maintaining a temp around 225-250

    Is this expected as the hardwood burn down to embers and the FB temps really ramp up? The CC started rising as the hickory turned to ember so I choked down the inlets, this is when the firebox seemed to be reaching 600+
    Last edited: May 12, 2016
  17. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Do not choke down both inlets in that situation....

    If the fire gets too hot, like you had, you have 2 options......

    1....   close the lower air inlet to reduce the heat of the fire...

    2nd....   open the upper air inlet to move heat from the FB to the CC....   

    FB temps should run 1-200 degrees above the CC temp or you are wasting wood....   that's why there are 2 inlets on the FB.....

    One to control the temp of the fire and the upper to keep the FB temp reasonable and move the FB heat through the CC....
  18. mike dula

    mike dula Newbie

    Thanks, Will give this a try next time. Its just going to take some cooking to get it down. I also noticed when the CC gets around 300 the door becomes stiff, the metal between the two hinges on the opening seem to be bowing a little when it gets hot making it stick. I think I'll add a vertical bar support on the inside of the upper chamber. 
  19. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Try relieving the hinges first...  Too close a tolerance can cause binging...  or oil the hinges...  use vegetable oil, mineral oil, pork fat...

    Is the door expanding or is the tank expanding....   the door and the tank, "should" expand at the same rate....

    Try taking the hinge pin out and replace it with a smaller diameter hinge pin..
  20. mike dula

    mike dula Newbie

    Thanks Dave, I put a little wd-40 on them, its not binding so bad I cant open it, it just gets stiff, takes a little effort. Its the tank, not the door. As it gets got the top of the tank, the section in between the two hinges bows up a little when hot. I can even tell more smoke is escaping through it as it happens. Not too worried about it, but wanted to fix it. I figured the door has the outer lip strap steel, the stop, and the handle so its a bit more reinforced. The top of the tank has nothing other than the hinges. Im thinking a section of bar tack welded vertically across the inside top of the top, basically when the upper door cut is would keep it from bowing. 

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