Mailbox mod & AMNPS tray for warmer/proofer build - Will this work?

Discussion in 'Other Builds' started by dward51, Feb 18, 2013.

  1. dward51

    dward51 Master of the Pit OTBS Member

    Question for the group.  I have not cut anything yet so this can be changed.

    I have a warmer/proofer that I need to get converted and I'm kicking around a new idea tonight.  This is how the air flow runs in the cabinet as it was built.  It has two air recirculation fans in the top and the heating element in the box also.  I like this idea as I would never have to worry about drippings on the element and I think it would be much safer (less of a grease fire hazard).

    As designed (no modifications) arrows show the normal air recirculation into the fan/heater box on top, down a side channel and back into the camber.  This diagram also shows my original plan of using the pellet tray in the bottom with a drip shield over it.  Not shown would be the air intake and vent/chimney.

    What I'm wondering is can I mount a mailbox mod to put the pellet tray on the side of the smoker about mid-level (I'm not getting any younger and thinking getting on my knees to check the mailbox if I mount it at the bottom will get pretty old quickly).  I would then take an iron pipe out the back of the mailbox, downward and enter the smoke chamber near the bottom floor.  The iron pipe would be capped and have holes on the sides for smoke flow.  Also there would be the exhaust chimney which is much higher than the mailbox to get the stack effect to move the air in through the mailbox, down to the chamber, up and out (also while the recirculation fans are moving the heated air & smoke around).

    So the question is does anybody know if a mailbox mod will draft downward and then upward like this?

    And the 2nd question is will the air recirculation setup be a problem?  I don't think it will as all the air the fans draw in is pushed back out at the bottom so there is no pressure change from the fan.  The intake flow would come from the mailbox intake and the chimney effect would keep the air/smoke moving out the top (as long as the heating element can keep up with the temp drop from colder smoke filled air I think it would work.  A damper on the chimney would let me control the flow as would a sliding baffle over the air intake holes on the mailbox).

    Any thoughts or suggestions?

    Last edited: Feb 18, 2013
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Dave, morning...... The AMNPS should burn for 10+  hours..... no need to monitor or do anything with it.....  Because you have a circulating fan in the box, I would put the AMNPS on the top rack in the smoker.... won't get dripped on and easy access...    perfect set up....

    I would put a piece of aluminum foil under it to keep the ash off of the food...   That all depends on how much wind speed is created by the fans of  course....      Dave
  3. dward51

    dward51 Master of the Pit OTBS Member


    If I put the tray on the top rack would not a lot of the smoke head straight out the exhaust vent?  Another thing I'm wondering about is the moisture content of the "air" inside the smoker & the pellets.  My thought was put the pellets in their own chamber and that is not an issue.  Yeah, I know I could just keep it simple (stupid) and put it in the bottom of the warmer like the first diagram, but the mailbox seemed to have more advantages "IF" it will work.

    Not sure which way I'll go yet.
  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I forgot about the moisture.... could very well be a problem.....  Does the chamber exhaust heated air to the outside ??  I would think it would be sealed fairly tight for efficiency.....   try it inside to see what problems develop, then we will figure out how to solve the problems.... that's what I'd do.... 

  5. dward51

    dward51 Master of the Pit OTBS Member

    No.  There is no exhaust and currently it is a sealed chamber with the door closed as I have not modified anything. The internal air just recirculates across the heating element in the top to evenly heat the food that would be kept in the cabinet as originally designed by McCall. 

    I'm know I'm going to have to add an inlet somewhere in the chamber and also add an outlet/exhaust vent added to make this a smoker.  Just want to cut the holes once so I need to be pretty certain whatever plan I go with will work.  The main question is the location of the tray and holes depending on which option I go with.

    I should also have said I intend to do both cold smokes and hot ones up to around 225*.   Since the unit would run to 240* "as is" I don't see much need to rip the insulation out but it is some form of foam, but it was foam made to work in a hot box.  Not going to see poultry at 375* in this unit but low and slow at 225* or sausage & stick at even lower should not be an issue.

    Worst case I could just go with the standard setup of pellet tray at the bottom covered by a shield and cut inlet holes with some sort of damper to control burn & airflow near the bottom (like in the first diagrams).  Either way I need to add an exhaust vent and stack at the top to get the smoke flowing up and out.

    Since the fans only suck air from inside the chamber at the top right edge and just move it from the top back to the bottom via vents in another chamber that runs on the right side of the box, the fans should not affect the air pressure and blow the smoke out of the smoker.  I'm pretty sure with either the pellet tray in the bottom or the mailbox mod on the side, the smoke should still flow up and out with some being recirculated and the rest being pushed out the top exhaust stack like any other smoker of this type from heat convection and the stack effect.

    I like the idea of the external smoke box/mailbox mod, as I don't have to worry about drips and if anything misses the catch pan in the bottom rack I would still have a sealed stainless interior bottom to make cleanup easier.  Also dry pellets would remain dry no matter what's going on in the smoke chamber with the external box.  So I could use a water pan if I wanted extra moisture and would not have to worry about any moisture picked up and recirculated by the fans back down to the bottom where the pellet tray would normally be.  I just want to mount the mailbox higher than at the bottom level of the smoker for convenience (I'm thinking about waist high). The outlet of the top vent would still be at least 4 to 5 feet higher than the mailbox (smoke would then flow down pipe into a hole in the side of the smoke chamber near the bottom).  It seems like it should draw like normal up and out after that, but I'm not certain.

    Or have I totally missed something?


    As I sit here typing this, I had a new thought. 

    I think I can test my theory of the pellet tray and downward air flow like the mailbox mod using two cardboard boxes and some cheap dry fit PVC pipe.    A junk pile proof of concept test. Only problem is the wife brought home whatever is going around and I've "got the sick" so it may be a day or two before I can test this.  Will post the results with photos either way.

    This is my cardboard box test solution diagram....

    Last edited: Feb 18, 2013
  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Looking at the fan enclosure.....   Where the arrow is entering from the warming chamber is the negative pressure side of the enclosure...  I would drill a 3/8" hole above the heating element area, where ever it was accessible, and install an exhaust tube to remove the moisture and smoke... that is the positive pressure side of the enclosure.... considering the proximity to the fan, that should be the highest pressure in the proofer and a 3/8" hole should be more than adequate..... that being done, where ever you put the "mailbox" the air should draw through it and supply enough air for combustion..  I would not put the MB mod on the right side of the proofer because you will have to drill through the air supply inlet channel....  On the left side would be much better near the bottom....  and I would couple the MB mod directly to the proofer with minimal ducting...

    One thing concerns me....  depending on the pressure in the fan enclosure, a 3/8" hole may be too large and too much air could be pushed out...  

    Does any of that make sense ?????

  7. dward51

    dward51 Master of the Pit OTBS Member

    Yes, it does.

    Actually the diagram is not 100% accurate.  The side chamber for the recirculated air stops about 6 to 8" above the floor of the cabinet floor so there is clear outside wall just like the left side there.  That is what led me to think about the mailbox mod pipe entry on that side.  Door opens to the right (handle on left and hinge on right side).  Where I want to put it on the porch will work out better if the mailbox is on the right also.  That way I can put in a cabinet with a work top to the left to set trays/racks of food on.

    As soon as I get over this funk I seem to have picked up from the wife, I will try the MacGyrver proof of concept test to see if the mailbox will draft downward if the exhaust vent is well above the inlet & mailbox (I think it will).  If that does not work, the the fan and pressure questions are moot until I get the smoke supply worked out.

    Just working out as much of this in advance before cutting anything as this cabinet is all polished stainless inside and out.  No aluminum, all stainless.   It's fairly thick stainless too. Thinking once it's done, I should take a microfiber buff ball and some flitz paste to the outside and it will be mirror polished (outside is a little duller than the inside as it was in a working kitchen).

    The cabinet is at my other house and I need to get over there and get some good detail photos and check the condition of the bearings, element, etc...  It does work when plugged it, but someone at the school had the top to the electric element/fan box open at one time before I bought it as they did not put it on all the way.  It ran for a few minutes when I hooked it up though.  I need to pull the fan motors and some of the other connection boxes as there is a lot of kitchen dust up there too.

    Here is a few photos from the original auction.  I need to take better ones.  In the photo of the interior you can barely see the air recirculation channel stops about 6 to 8" above the bottom (and if my memory is correct, it is capped on the bottom as well).  Pipe could come through the right side below that.  All the stuff sitting in the bottom is the rack supports that mount on the sides (removable and adjustable). They also left me two new looking dial thermometers that would sit or hang in the chamber.

    EDIT ------------------------------

    One more point.

    I was initially torn about pulling the foam insulation or leaving it.  Depends on who you ask as the the answer to that.  Nepas and others have taken warmer/proofers and left the foam in place with no problems.   Builders in other forums say unless you go over 250* don't worry about it at all in a heated box like this. Now if it was a fridge unit, no question it should be pulled, but this unit is made to get hot and stay hot all day.

    Tapping on the door, it has that foamed in place sound.  Also one corner of the magnetic strip seal had been pulled off the inner door panel and you can see it's foamed in place with no voids and there is a plugged hole in the front of the door for an optional dial thermometer that when I remove the plug can see the blown in foam. 

    HOWEVER!!!!!!  The back, top and sides when tapped from either the inside or the outside do not have that foamed in place sound and there is also flex in the surface so it's clearly not foam out to those panels.  It looks like there is a top plate that all the fans, heater, boxes, etc... mount to that is screwed down from above and I think if I unscrew that I can have access to the top of the side and back areas.  I'm wondering if they had foam panels that were just slid down in the channels formed by the inner box and outer walls.  The company info says foam insulation, but does not state if it was blown in or panels slid in.  If it's panels, I'll pull them and replace with Roxul or similar and not have to trash the box to get this done.  The inner skin of the door pops out and I could deal with that blown in place foam.

    I'm planning on pulling all the workings from the top to clean and verify electrical condition anyway so unscrewing that top to see about the other foam is a might as well.
    Last edited: Feb 19, 2013
  8. Dward, Dave and I have had a few PM's over this very subject. I will watch your experiment with anticipation of a successful outcome!

    I have an idea (remember I don't know chit!)

    What if we introduced the smoke at the fan? Drill a slightly larger inlet hole in your mailbox that the inlet into the fan area...(see drawing) Then for exhaust drill a slightly smaller hole to keep the pressure up inside the cabinet? Dave, what are your thought on this? I apologize for the crude drawing, but it's late and I want to get the idea across...before I went to bed!

    Obviously the fan and all would get the smoke residue (although pellets burn fairly clean?) by a anal maintenance schedule would help that a bit (assuming access is readily available?)

    My tube smoker should be here Friday....

  9. dward51

    dward51 Master of the Pit OTBS Member

    I think the positive pressure created by the fan output would probably push the air down the tube to the mailbox and the smoke would end up going out the air intake holes on the mailbox.  Looks like that would work the opposite of what I need.  In essence it would make the exhaust vent/stack on top the air inlet and force it out through the mailbox.

    Or did I miss something?
  10. You didn't missing anything, I'm sure there's a way to use the fan to "pull" the smoke into the chamber...I'm up against the same challenge, how do I keep the internal/non-vented fan from pushing all the smoke out? My fans are more for high volume/low pressure. I plan on using my tube smoker somewhere in the CC?!

    Here's kinda what I'm thinking? My fans (I assume similar to yours) blow down the inside of the tuning plate, which has progressively more holes as you reach the bottom of the plate/CC.

    I'm interested in what you decide? I really like the idea of having a side mounted box (I even thought about some of the side mounted puck and/or pellet smoker add-on?)

  11. dward51

    dward51 Master of the Pit OTBS Member


    I saw your photos of the cooker in the other thread.  You stole that one for sure!!!!!  That is a great looking cooker and is made to go to a lot higher temps than mine.

    Depending on how I feel tomorrow, I may try the cardboard box mock up.  The wife picked up a bug from her office last week and apparently brought it home to me.  Yesterday and today were not fun.

    I'm not certain if the recirculation is going to be an issue or not as every bit of air that it pushes out it also sucks in and both are within the same chamber so in effect it is a zero net sum gain.  I believe the natural heat convection upwards will want to exit via the top vent and if a longer vent pipe is used this will naturally want to start the flow up and out of the chamber no matter where we place the inlets.  If necessary, just make the chimney pipe taller and the effect is greater.

    That being said, I'm not sure if the cardboard box mock up with the mailbox side unit will draft as with no heat source where is the convection.  Same for cold smoking with no heat.  I guess the only way to find out is mock it up and see.

    Will let you know.
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Dave, morning..... Figure out if you can run the fan without heat....  would be great for cold smoking and drying meat before smoking and forming the pellicle on fish....

  13. At our altitude the TUBE works better than the AMNPS in smaller spaces, maybe the fan will help.
  14. dward51

    dward51 Master of the Pit OTBS Member

    Yep, fans and heating element are independent of each other.  That's one reason I really hope this will draw properly without heat as I would like to cold smoke also.
    I'm at about 790' above sea level according to GPS.
  15. Dave,

    Hope you and the misses are feeling better?

    Not sure if you've made in progress on the smoke front? I've still been brainstorming on "how" to get the smoke into the chamber? I liken our units to a small house with a forced air furnace...we can still have fires in our fireplace without it pushing the air out, so there should be no reason why I can't put the AMNTS inside? I should be "okay" as long as I don't get too crazy with the differentials in inlets and exhaust?

    For your design, I was thinking, maybe put an inline fan before the mailbox (or attached directly too?) that uses positive pressure to push the smoke in? Like a small dial controlled computer fan, higher volume, lower pressure? Just an idea? (I'm sure you've thought of this?)
  16. z
    Last edited: Oct 16, 2013
  17. dward51

    dward51 Master of the Pit OTBS Member


    I'm pretty much over the bug the wife brought home from her work, but we had another detour which has delayed the cardboard box testing.   But it was a good detour.  Daughter called from college yesterday and said she won a $200 prize for one of her prints in a gallery exhibit.  So we HAD to drive out to see her and the gallery exhibit today.  She had previously sold a few pieces but this is the first cash award she has won (and we still have the print). So we drove out and spent the afternoon with her and her room mate and took them out for dinner tonight to celebrate.

    Of course now it's raining and is predicted to do so here for the next few days.  Eventually I'll get to test the smoke flow theory using the cardboard box mockup.  But for now..... stand by
  18. dward51

    dward51 Master of the Pit OTBS Member

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