Vertical built, looking for tuning pointers

Discussion in 'Reverse Flow' started by uncre8tv, Apr 28, 2015.

  1. Started a VRF build with a couple of things in mind:

    1 - wanted to teach myself to weld (still a work in progress - don't zoom any of these pics!)

    2 - unhappy with the ability of my little/cheap side-by-side to hold heat. figured a heavy vertical has to heat better, right?

    So I sketched up some basic ideas and went to work.

    - 1.5"x1" tube is my frame - 1" provides me an insulation dimension on the outside. 1.5" provides my dimension for the vertical runners.

    - 1/4" plate for the floor of the cook chamber and the fire box. so the baffle is 1/4" steel (plus any water pan I may throw in)

    - 2x4" 1/8" wall rectangle tube for the exhaust.

    - 2x 2" ball valves for intake (one high, one low, centered)

    - 16ga for all the inner walls.

    - 1" ceramic blanket insulation.

    - silicon tadpole gakset for doors.

    - cheap amazon hinges and latches.

    - 20ga for outer walls.

    - various angle and scrap as needed (inner door frames, etc)

    Got the frame and inner walls together, along with the doors and door frames. Ran my first test fire last night. No basket so just a few coals and a hunk of wood on the floor of the fire box. Got a very good looking draw. A few minor leaks as expected. Didn't see the temp push past 150 in the cook chamber, even with the valves full open. Hoping that this is just due to the coals on the floor, and the short load of coals. But, I also didn't do any real math on this thing. So I'm wondering if I need to tune (embiggen) my exhaust opening a bit. Right now it's a ~2.5x2.5" hole I chopped out with a cutting disk. Maybe pull my inside walls down some too. Hopefully raising the fire will be the easy way to get some temp though. 

    Outer walls and insulation aren't on yet, obviously (also racks and rack runners aren't in, less obviously.) Wanted to run a few test fires to find my leaks before I put on the insulation and skin so I'm not smoking my insulation too bad.

  2. I think your exhaust port should be at least 2"x4" to match the exhaust pipe cross section. I think it is safe to say if you have no leaks, then go ahead and insulate it. I would not pull the inside walls down any more until after you have it insulated and fire it up again with a reasonable fuel load. These cabinet smokers rely on the insulation quite a bit to get the temps up, so you should see a marked improvement from that.

    One more thing to consider is that your air intakes might be overkill for that size smoker. Running with the upper intake wide open might actually cool your cook chamber rather than help it.
    Last edited: Apr 28, 2015
  3. Thanks. I did notice it cool a bit when I cranked them both open. Max temp was maybe 1/5th open up top and anywhere from 1/3rd to full open on the bottom (didn't seem to make much difference.) I did kill it by closing off the top and putting the bottom 1/5th open. So I know I've got the ability to close it down enough. Putting in shelves tomorrow (started tonight) so while I'm in there with the grinder I'll put a cutting disk on and open the exhaust up a bit.
  4. daveomak

    daveomak OTBS Member SMF Premier Member

    unc, morning.... Try running the smoker with the exhaust wide open and controlling the temps with the air inlets....

    Also, with normal smokers, a dual air inlet system seems to work well.... lower inlets for fire temp control and upper air inlets to move air through the firebox and smoker body... with those to inlet systems, some really good temp control can be had....

  5. Sorry for my poor word choice. "Up top" is just the top intake... I guess it's not really "up" just above the lower intake. The exhaust is un-baffled at this point. Haven't had a chance to run another test fire yet, building a coal basket and still need to cut my exhaust hole bigger.
  6. Getting my coal basket in did the trick. Nice hot seasoning (didn't spray sides because I wasn't sure I'd make heat.) So I'll do it again this weekend.  

  7. Excellent!
    Nice level of control.

    Did you also open up the exhaust?
    Last edited: Apr 30, 2015
  8. Thanks! I ended up not opening up the exhaust. I had been guessing at the cutout size, but I took a tape measure to it today and it was actually 3x3 (9" square) which is bigger than the 2x4 (8" square) exhaust. 

    Tonight I got about 2.5hrs out of a full chimney and a log and a half (revised from calling it two logs, one was half burned.) Opened it up and it was all burned to ash just now, a few glowing chips but no real fuel. That's with letting it spike hard at the start. Also there was room for probably another chimney and log in the basket. A little better control at the beginning (and the insulation) should see this be nearly a "set it and forget it" cooker, I think. 

    Tomorrow - door gasket improvement, shelves (shelf runners are in)
    Weekend - insulation and skin? We'll see if I find the time (and if I get my FIL to come by - he's an old HVAC man so I'm counting on him to have some magic tricks with the 20ga.)

  9. Fantastic!

    Old HVAC guys are worth their weight in gold for that kind of work.

    I am just about to skin my offset reverse flow. Decided tools were what I needed. Went to HF and found an electric shear that is good for 14ga on sale.

    Keep us posted. I really like the size of that cabinet. So many huge ones out there it is nice to see a more compact model come together.
    uncre8tv likes this.
  10. Never did get my FIL out here, but just ended up hammering the 20ga over the corners. Welds looks terrible, but most are hidden. I'll probably have him help me re-make the top cover at some point. Needs balance, paint, a few bits of trim... will run another test fire next weekend and probably a "real" run with food before I paint it (due to impatience more than anything.) Never did do the math on the weight until after I got it upright on the stand. Heavy for it's size, at least 340lbs or so. It was an adventure to get it stood up myself. 

  11. Looks great. Nicely done!
  12. First live meat test. 3.5 hours, just about to foil it. Also have a small end of a picnic shoulder in, skin on so I'm not foiling that.

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