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Double wall with sand insulation??

maytag

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Being from the northwest quickly changing weather can screw up any outdoor cooking quickly. I've been thinking of what is the most effective thermal insulation that is cheap and worry free... hence the sand. By building the smoker with a double wall I could leave space to fill with sand once the smoker is in it's final location.

It seems that having this big thermal mass will help with consistent temps and not let the outside conditions effect the cooking.

Aside from a long time to get everything up to temp initially (might need a gas assist), are there any downsides to this idea?

What would be the best style of smoker for this?  Vertical? Horizontal? Double Pass? 
 

forluvofsmoke

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You are correct in all aspects of the benefits of adding thermal mass. A double-walled cabinet filled with sand would help the smoker shrug off wind gusts, short-term precipitation, and, to some extent ambient temp swings. More initial thermal energy to stabilize temps, and possibly a bit more throughout the smoke would be noticed, though this would be a more constant rate of consumption once the desired temp is reached. The more mass you add, the more thermal energy release required to heat it up, and slightly more to maintain temps compared to a lighter built cooker.

If I were to use this type of thermal mass for a new build, I would go with a vertical cabinet, wide-body. All three walls and the door with the same density, and possibly the roof as well...and a high temp door gasket as a final touch for added efficiency. If your method of smoke generation could require tending, or refilling a water pan, I would add a drawer or bottom door for access to these levels in the smoke chamber, and use thermal mass in the front of it as well. The extra opening would allow for better heat retention in the smoke chamber during tending.

If you're planning on a charcoal-fired smoker, I suspect that the Minion Method won't get you hot enough without temps running away after you reach your desired cooking temp. You could, however, start with a smaller, hotter fire for start-up, then switch to the Minion method by adding unlit after a period of time. A propane burner would be an easy to use fix as well...just get to temp first, then build your fire and kill the burner...obviously, there would be a learning curve involved with figuring out how much burning vs unlit charcoal to use when you build the fire, if Minion will be your route.

Down-sides? As you hinted about filling the gap with sand after it is in it's final place for use, I would do the same. A 1/2" - 3/4" gap between the walls could take a few hundred pounds of sand to fill, depending on the cabinet dimensions. So, no, it won't be a portable rig at that point, unless you have a sturdy carriage and casters to rest it on. If you figure up about how much thermal mass (weight, in specific) that you want to add, then calculate the volume (on-line calculators are available for conversion by material density over volume), then you calculate the actual gap measurement to use between the walls to get the amount of added mass you want based on surface dimensions of the walls, door, and roof, if you want extra mass there.

The alternative would be to use heavy-gauge steel to achieve the desired thermal mass for the smoke chamber (much more expensive than sand).

Either way, you don't want to have too much thermal mass that requires exorbitant amounts of energy to bring it up to temp, unless your intended fuel will be hardwoods...then, the extra mass helps you to be able to use a hotter fire more effectively to avoid excessive smoke.

Let me know if you need help finding a way to make your calculations for added thermal mass...I'll do some digging and post a link or two, if needed.

Eric

EDIT: I just found your roll-call thread...a couple thoughts came to mind on your smoker build: if you wall-in the smoker with brick or block (smoker built into your outdoor kitchen), leaving a small gap on the side/rear walls of a cabinet smoker as an insulating space, you could just add thermal mass to the door and possibly the roof, then, fore-go the double-wall and thermal mass on the sides and rear of the cabinet. This would give excellent protection from weather, and use a bit less fuel overall. If you designed the structure based on the smoker itself, you could vent from the upper-rear or top (your choice) and cover the entire smoker, except the door(s), and the combustion air inlet port(s). I would advise that you cover the inlet with a metal screen on any permanent installation (bugs and other little critters like to crawl into small spaces where it's nice and cozy), and clean-out of these areas should be considered in the design as well.
 
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daveomak

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Maytag, morning and welcome to the forum..... an additional thought on using sand for thermal mass....  Think about pinning the double walls with bolts or blind welding with some sort of steel pin.... in the event the walls expand and contract... they will not bulge, maybe...

One thing to remember, thermal mass takes time to heat to operating temperature... the more mass you have, the longer it will take to warm, and it will take more fuel to heat it up...  Dave
 

maytag

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Thanks for the replys

I do hear you on taking longer to heat up, I added 125lbs of fire block to my dad's traeger and it takes at least 2x longer to get to temp, but once it's there it uses barely any pellets to keep the temp consistant, which means better smoke. I did have to reinforce the chassis of the traeger to support this as well.

Ralising I'm kind of lazy, I am thinking of building my "eventual" smoker using an auger pellet feed...just out of thick stainless so it doesn't rot like the traeger. I think you are right about the Vertical style for ease of insulating, with the pellet feed and gas for pre heating it could be very user friendly.

Question on cooking on a vertical smoker though, would there be a lot of difference between the different rack heights? I have only used horizontal, double pass, and rotiserie style before.
 

s2k9k

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Thanks for the replys

I do hear you on taking longer to heat up, I added 125lbs of fire block to my dad's traeger and it takes at least 2x longer to get to temp, but once it's there it uses barely any pellets to keep the temp consistant, which means better smoke. I did have to reinforce the chassis of the traeger to support this as well.

Ralising I'm kind of lazy, I am thinking of building my "eventual" smoker using an auger pellet feed...just out of thick stainless so it doesn't rot like the traeger. I think you are right about the Vertical style for ease of insulating, with the pellet feed and gas for pre heating it could be very user friendly.

Question on cooking on a vertical smoker though, would there be a lot of difference between the different rack heights? I have only used horizontal, double pass, and rotiserie style before.
I assume you meant temp difference?

I have a GOSM vertical propane smoker and there is only about 5* difference between the top and bottom rack and they are about 18" apart, and the top rack is hotter.
 

forluvofsmoke

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Yeah, with a new vertical smoker build, you may need to experiment on water pan shape (taper of side-walls), but most importantly, size (clearance from the smoke chamber walls) and height from the heat source to get the least amount of temperature differential between grate spaces. I ran into this issue with a double/stacked (2 barrel smoke chamber) vertical Brinkmann Gourmet charcoal smoker. With the increased height of the smoke chamber, I had up to 80* temp differential, hottest being on bottom. I used a charcoal pan from a Brinkmann Smoke n Grill for the water pan, and the larger diameter pan had much less clearance from the smoke chamber wall. The temps came in at just over 10* differential most of the day, with a bottom to top grate distance of over 19".

Think of the water pan as a heat baffle which allows true indirect cooking in a vertical smoke chamber. Remembering the baffling effect will help you to determine which corrective measures to take, but I think in most cases, if too hot down low, use a larger baffle/water pan to carry more heat along the smoke chamber walls before it traverses across towards the center of the smoke chamber. Water pans also act as a drippings catch so you can avoid flare-ups, and reduce the effects of direct cooking when the pan is wet. A dry pan acts as a baffle and a thermal sink, to some extent, but will soon turn into a direct heat source, depending on it's mass and proximity to the heat source.

With water pans, distance from the heat source and capacity will determine how much increase in smoke chamber humidity (distance) and duration of added humidity between refills (capacity).

You can get better smoke reaction with higher humidity, but this can be a double-edged sword of sorts, if the humidity remains high throughout the entire cooking process. If you remove the added humidity about mid-smoke, it allows the meat's surface fibers to dry and shrink becoming a less porous surface...this seems to help a lot with interior moisture retention and bark development for your meats that are cooked to higher finished temps, such as pork butts for pulled pork, or brisket, and even my no-foil ribs seem to be far more moist. Being you're planning to build a new rig, you may want to consider the smoke chamber humidity and being able to remove the pan to dump the water and return it to the smoke chamber dry for the finishing stage of cooking. If I smoke in a wet chamber the whole time, I get a bit drier meat when finished at higher internal temps. Using a wet to dry smoke chamber humidity without foiling the meat to reach finished temps has been one of my experimental projects this summer, so I vouch for the results...just something to think about.

Eric
 

wes w

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I am in the final stages of completing a outdoor brick smoker.  Between the firebrick and block I stuffed it with fiberglass insulation.  Of course you have to keep it dry during the build.  I have a outdoor fireplace just to the left  and plan to feed the smoker with the hot coals.   There is a shelf between fire door and food doors where I will place the water pan.  Once the firebrick warm up to temp.  there will be little to no heat lose by opening the doors.

 

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