Downflow Mailbox mod - proof of concept testing (MacGyver special) w/ photos

Discussion in 'Other Builds' started by dward51, Feb 24, 2013.

  1. dward51

    dward51 Master of the Pit OTBS Member


    Last week I posted the question will a Mailbox Mod downdraft to the bottom of a warmer cabinet smoker conversion if the mailbox is mounted mid level of the smoker.  After a while I figured, time to field test this concept before cutting a stainless steel smoker cabinet.  So after being sick for a few days and rain for a few more, I finally was able to test this concept out today.

    So, here we go.....

    This is the idea and the photo of my cardboard proof of concept mockup.  The AMNPS pellet tray is inside the simulated mailbox.   A small air inlet vent is cut on the right side of the "mailbox" and the outlet is on the upper left center of the "mailbox". Outlet is 1" PVC pipe.  I know this is a little smallish, but it's what I had in the basement that I had right angle fittings for.  Smoke flow should then be down the 1" pipe to the bottom of the simulated warmer cabinet smoker.  If this works, the smoke will then flow up throughout the "cabinet" and out the 1" PVC "Vent" at the top.  No fans were used to move air in this test.  Only the natural air flow for the AMNPS was used.

    Fire up the AMNPS pellet tray with some oak pellets.  Blow out the fire and let it smoke for a few minutes.

    Into the simulated "Mailbox" goes the lit AMNPS pellet tray. Smoking just fine now.

    Tape the "mailbox" shut and start the timer on how long before we see smoke at the "smoker cabinet" vent.

    4 minutes in, we have smoke exiting the vent ! ! ! !

    I found out it's harder to photograph thin smoke than it is for you to see it in real life.  I had a slight wind which made this task even more difficult.  Although in this photo taken at the 4 minute mark, it does not look like much smoke is coming out, there was a fair amount.  (NOTE*** I also believe the 1" PVC downdraft pipe and vent pipe were undersized, but for this test it worked.  A larger diameter should work better IMO).

    At the 10 minute mark I added a longer section of vent pipe to the simulated smoker cabinet to see if the added height would draft better.  I believe there was some improvement, but again this 1" PVC was undersized and a larger diameter for all pipe would be better.

    Proof the concept will work.  This photo is from the extended vent pipe.

    A better shot (like I said, thin smoke can be hard to capture in an image sometimes)


    Yes, smoke from an AMNPS pellet tray will draft downwards and then back up in a mod like I proposed.

    There was some tendency for the smoke to also want to draft back out the inlet vent on the cardboard box used to simulate the mailbox.  I do believe a 3" duct instead of the 1" PVC used in this simulation would give much better draw.  But it appears to work.

    Next thing I have to resolve is will it draw in the modified cabinet as I also have those internal air recirculation fans that blow air over the heating element (which is at the top of the warmer cabinet) and then evenly back into the main body of the cabinet.  I think it should work as the air moved out of he cabinet via those fans equals the air put back in near along that vented chamber on one side so there is no real pressure change overall in the cabinet from those fans (in theory anyway).  I also believe the natural convection of the heated air upward and out the top vent of the converted warmer will enhance the downdraft flow from the mailbox mod tested here.  But this test shows it *WILL* work in a cold smoke situation, but it will probably work better with a larger feed pipe and warm air convection.
    Last edited: Feb 24, 2013
  2. Bravo!!! Nice experiment...

    I'm from the "nah, I only paid $50 for it...let's drill some holes and see what happens"

    You saw the aftermath!

    Now, it's time to smoke a little sumthin', sumthin'!

  3. z
    Last edited: Oct 16, 2013

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