Door Designs

[A_Stubbed_Toe]

Hey everyone,
I am in the beginning stages of designing the smoker I am going to build. I was wondering if you guys could post your favorite Door Designs or anything you can possibly think of when it comes to designing the doors.

[ajfoxy]

That would depend on the type of smoker you are planning to build. Square, round or whatever. Nicest one I've seen of late has been reelfishy's 120 gallon smoke punk build. Do a search on the forum for ideas on that one.

[Rodcrafter]

I'll tell you that squared doors are better than round doors. This pit has three types, and the door on the right is far better.

jm2cw

[ajfoxy]

RC... that's one gravity defying unit you have there. I'm impressed

[Rodcrafter]

RC... that's one gravity defying unit you have there. I'm impressed

I know! Right AJ? Silly picture resizing stuff, you have to click on the pic to make it turn over.

[Big T]

I thought RC was posting that picture for the guys down under

[Frank_Cox]

Yep, what ajfoxy said....
What type of cooker are you wanting to build?

[A_Stubbed_Toe]

SO I am planning to build a Square Reverse Flow smoker. I have not found the definitive thinner metal & insulation or just thicker metal. I really love the idea of incorporating a santa maria style grill for the firebox top to use when I want to grill, but I have not yet figured out a way to get that done. I've got young kids that love to run around and "help" me put wood on the fire and the thought of added safety is nice.

60" CC seems like it would be more than enough most of the time for my needs. I'm thinking somewhere around 24"-30" deep, but I am not sure yet. Definitely think I am going to figure out a propane starter assist for it, and I'm not quite sure but I feel like I am forgetting some things.

I have a few questions for you guys. Is there a downside to having a firebox that is oversized? and at what point does it become oversized for the ratios and effect convection within the CC, and how would it effect convection?

Also, if I were to go the route of insulating the smoker could I theoretically use a different material besides metal for the skin, like Ipe for example or some other beautiful hardwood? That is after taking into account heat transfer from the standoffs where you would attach the decorative wood, and the exposure to the elements.

Thanks a ton you guys. You guys are an incredible resource

[Frank_Cox]

sounds like a great project!
the only thing I would keep in mind when making a grill option for the firebox is making sure the firebox doesnt leak air too much. not for losing heat but for sucking in too much combustion air. it would make it hard to shut down if it should overshoot temp.
that being said, I think the santa maria grill option would be amazing!
On the oversizing of the firebox, I usually make the oversizing maximum about 115%. if you go much higher than that you will have a hard time with temp swings. the firebox will take as much combustion air as you let it have so more storage room= more difficulty to control temp. keep in mind, we are dealing with a slight negative pressure in the firebox and lower as we get to the cook chamber once the pit is settled in and running at temp.
I think an alternate finish material would be real nice! If you do this, I would recommend using Roxul insulation or something with a higher heat rating like KaoWool. make sure the insulation can not get wet or have condensation issues so it does not lose it's R Factor.
sounds like a great project!

[A_Stubbed_Toe]

Thanks for all Help Frank, Is there a detailed thread or sticky anywhere that describes principles of thermodynamics as it relates to smoking? I dont understand why the firebox would have a slight negative pressure. Unless it means that the firebox itself is in a state of negative transfer of heat/work/enegry? Which would mean the pressure in a given chamber is relative to the environmental conditions at a given moment, which would remain a constant 0, or neutral, in this instance because The smoker will always be our template.

Does that make any sense and how wrong am I? I hated alchemy and physics when I was younger so I can't recall much.

[A_Stubbed_Toe]

sounds like a great project!
the only thing I would keep in mind when making a grill option for the firebox is making sure the firebox doesnt leak air too much. not for losing heat but for sucking in too much combustion air. it would make it hard to shut down if it should overshoot temp.
that being said, I think the santa maria grill option would be amazing!
On the oversizing of the firebox, I usually make the oversizing maximum about 115%. if you go much higher than that you will have a hard time with temp swings. the firebox will take as much combustion air as you let it have so more storage room= more difficulty to control temp. keep in mind, we are dealing with a slight negative pressure in the firebox and lower as we get to the cook chamber once the pit is settled in and running at temp.
I think an alternate finish material would be real nice! If you do this, I would recommend using Roxul insulation or something with a higher heat rating like KaoWool. make sure the insulation can not get wet or have condensation issues so it does not lose it's R Factor.
sounds like a great project!

I mean the environment is 0 because it is inherently neutral and attempting equilibrium with the smoker. Do you mean that the firebox has more negative pressure than the Cook chamber?

[Squiggle]

Yeah I’m a big fan of square doors, more room, looks neat & you don’t have to worry too much about the cut out springing or warping.

Thanks RC, I knew you were thinking of us

[Frank_Cox]

A_Stubbed_Toe,
I'll explain best I can... here we go...
lets define some measurements of pressure first.
we measure pressure at sea level at 0 psig (psi gauge) when actually it is 14.7 psia (psi absolute) also, 1 psi is equal to 28 inwc (more precisely 27.707 inwc... Inches water column). negative pressure is measured as "inhg" (inches mercury)
so when you hear someone say "static pressure" (in this case anyway) we are talking about the difference between the pressure inside of a space and the pressure outside that same space. in a residential hvac system typically the duct is designed for less than 1 inwc static pressure... more like .5 inwc. that is a very slight amount of pressure.

keep in mind 2 more things...
-air is always trying to move from an area of high pressure to an area of low pressure.
-air is a fluid and has mass to it. so to keep pressure constant in a space, the only way air can come out is if more air goes in or something else fills the space to replace it. if the amount of air volume or mass in the same space changes then so does the pressure.

so to make my point, the fire is consuming air for combustion so for air under a natural draft to move from outside the firebox to the inside of the firebox it will need to be in a lower pressure than the exterior of the firebox.
now going further along the path of airflow the cook chamber would then also need to be under a "draft" or a slightly lower pressure.
at this point we are seeing what is referred to as the "chimney effect". the chimney effect in a smoker is caused when the cook chamber heats up and the smoke stack also warms up and the warm air mass wants to rise up and out of the cook chamber then pulling the remaining air mass out with it which continues to increase in velocity and draws harder on the air mass below it as the stack gets warmer.
so if the air outside the firebox is at a higher pressure than the air inside the firebox and the pressure outside the firebox is 0 psig then the pressure inside the firebox must be less than 0 psig. once we get into a negative pressure we start to measure this as "inhg" or inches mercury.

hope this helps and I didn't confuse anyone.

[Big T]

BTU'd

[ajfoxy]

Excellent summation Frank, but a tad way over my head.

I'd always just looked at it from the viewpoint of hot air rises (in the case of a smoker, out the chimney) creating a draft which pulls cool air in from wherever it can. Probably overly simplistic, but it seems to match my thought process which is generally a tad simple.

I think I do like your explanation better... it has more words...

[Squiggle]

BTU'd

[A_Stubbed_Toe]

Excellent summation Frank, but a tad way over my head.

I'd always just looked at it from the viewpoint of hot air rises (in the case of a smoker, out the chimney) creating a draft which pulls cool air in from wherever it can. Probably overly simplistic, but it seems to match my thought process which is generally a tad simple.

I think I do like your explanation better... it has more words...

A_Stubbed_Toe,
I'll explain best I can... here we go...
lets define some measurements of pressure first.
we measure pressure at sea level at 0 psig (psi gauge) when actually it is 14.7 psia (psi absolute) also, 1 psi is equal to 28 inwc (more precisely 27.707 inwc... Inches water column). negative pressure is measured as "inhg" (inches mercury)
so when you hear someone say "static pressure" (in this case anyway) we are talking about the difference between the pressure inside of a space and the pressure outside that same space. in a residential hvac system typically the duct is designed for less than 1 inwc static pressure... more like .5 inwc. that is a very slight amount of pressure.

keep in mind 2 more things...
-air is always trying to move from an area of high pressure to an area of low pressure.
-air is a fluid and has mass to it. so to keep pressure constant in a space, the only way air can come out is if more air goes in or something else fills the space to replace it. if the amount of air volume or mass in the same space changes then so does the pressure.

so to make my point, the fire is consuming air for combustion so for air under a natural draft to move from outside the firebox to the inside of the firebox it will need to be in a lower pressure than the exterior of the firebox.
now going further along the path of airflow the cook chamber would then also need to be under a "draft" or a slightly lower pressure.
at this point we are seeing what is referred to as the "chimney effect". the chimney effect in a smoker is caused when the cook chamber heats up and the smoke stack also warms up and the warm air mass wants to rise up and out of the cook chamber then pulling the remaining air mass out with it which continues to increase in velocity and draws harder on the air mass below it as the stack gets warmer.
so if the air outside the firebox is at a higher pressure than the air inside the firebox and the pressure outside the firebox is 0 psig then the pressure inside the firebox must be less than 0 psig. once we get into a negative pressure we start to measure this as "inhg" or inches mercury.

hope this helps and I didn't confuse anyone. [emoji481]

Thanks a ton Frank for diving into this with me. So basically I was somewhat on the right path in earlier posts. Environment=0 and the smoker is working towards equilibrium. So next question is, why is there smoker, or what makes the smoker a lower atmospheric pressure than the outside? Is it inherently lower, or does the presence of heat, causing air to leave the firebox, therefore reducing the mass inside the area cause the pressure to be lower?

For the purpose of example, if we were to close the chimney dampener, let's assume the fire just stays lit, the mass of air within the CC would cause the pressure in the CC to rise enough to force air against it's natural path and out the FB intake. And, if we were to crack the chimney dampener just "enough"....... Wait, is that what a "backdraft" is? And a backdraft only lasts until the pressure in the CC, "behind" the fire, drops below the amount of pressure in the fb.

So only if the above is correct, do you mind moving on to step 2? Which would be how the ratios and openings effect the chimney effect. Actually I think I can deduce it, however I don't know what the ideal smoker flow would be. .5?

Sent from my Moto Z (2) using Tapatalk

[bigbook]

Excellent summation Frank, but a tad way over my head.

I'd always just looked at it from the viewpoint of hot air rises (in the case of a smoker, out the chimney) creating a draft which pulls cool air in from wherever it can. Probably overly simplistic, but it seems to match my thought process which is generally a tad simple.

I think I do like your explanation better... it has more words...

A_Stubbed_Toe,
I'll explain best I can... here we go...
lets define some measurements of pressure first.
we measure pressure at sea level at 0 psig (psi gauge) when actually it is 14.7 psia (psi absolute) also, 1 psi is equal to 28 inwc (more precisely 27.707 inwc... Inches water column). negative pressure is measured as "inhg" (inches mercury)
so when you hear someone say "static pressure" (in this case anyway) we are talking about the difference between the pressure inside of a space and the pressure outside that same space. in a residential hvac system typically the duct is designed for less than 1 inwc static pressure... more like .5 inwc. that is a very slight amount of pressure.

keep in mind 2 more things...
-air is always trying to move from an area of high pressure to an area of low pressure.
-air is a fluid and has mass to it. so to keep pressure constant in a space, the only way air can come out is if more air goes in or something else fills the space to replace it. if the amount of air volume or mass in the same space changes then so does the pressure.

so to make my point, the fire is consuming air for combustion so for air under a natural draft to move from outside the firebox to the inside of the firebox it will need to be in a lower pressure than the exterior of the firebox.
now going further along the path of airflow the cook chamber would then also need to be under a "draft" or a slightly lower pressure.
at this point we are seeing what is referred to as the "chimney effect". the chimney effect in a smoker is caused when the cook chamber heats up and the smoke stack also warms up and the warm air mass wants to rise up and out of the cook chamber then pulling the remaining air mass out with it which continues to increase in velocity and draws harder on the air mass below it as the stack gets warmer.
so if the air outside the firebox is at a higher pressure than the air inside the firebox and the pressure outside the firebox is 0 psig then the pressure inside the firebox must be less than 0 psig. once we get into a negative pressure we start to measure this as "inhg" or inches mercury.

hope this helps and I didn't confuse anyone. [emoji481]

Thanks a ton Frank for diving into this with me. So basically I was somewhat on the right path in earlier posts. Environment=0 and the smoker is working towards equilibrium. So next question is, why is there smoker, or what makes the smoker a lower atmospheric pressure than the outside? Is it inherently lower, or does the presence of heat, causing air to leave the firebox, therefore reducing the mass inside the area cause the pressure to be lower?

For the purpose of example, if we were to close the chimney dampener, let's assume the fire just stays lit, the mass of air within the CC would cause the pressure in the CC to rise enough to force air against it's natural path and out the FB intake. And, if we were to crack the chimney dampener just "enough"....... Wait, is that what a "backdraft" is? And a backdraft only lasts until the pressure in the CC, "behind" the fire, drops below the amount of pressure in the fb.

So only if the above is correct, do you mind moving on to step 2? Which would be how the ratios and openings effect the chimney effect. Actually I think I can deduce it, however I don't know what the ideal smoker flow would be. .5?

Sent from my Moto Z (2) using Tapatalk

Made from 1-1/2 " angle. Squared up and cut into end of tank. Flat plate for door . Works wonders

Sent from my XT1585 using Tapatalk

[Rodcrafter]

The lower pressure in the FB comes from the fire in the beginning. Then after the whole smoker was heated up it all contributes to the lower pressure as it becomes draft. This is why in the beginning you may need to leave the door of FB open until things begin heating up. If you have leaks in your CC door it robs draft from the FB circumventing the process.


Making memories!

[Frank_Cox]

Thanks a ton Frank for diving into this with me. So basically I was somewhat on the right path in earlier posts. Environment=0 and the smoker is working towards equilibrium. So next question is, why is there smoker, or what makes the smoker a lower atmospheric pressure than the outside? Is it inherently lower, or does the presence of heat, causing air to leave the firebox, therefore reducing the mass inside the area cause the pressure to be lower?

the air mass is lighter since it is being heated by the fire and expanding. also its properties are changed since now there is byproducts of combustion added after the air mass leaves the firebox. the lower pressure is caused by the draw of the hot air mass leaving the cook chamber. the cook chamber would continue to pull lower in pressure until it finally was in a vacuum unless air is drawn in to replace what had been exhausted.

For the purpose of example, if we were to close the chimney dampener, let's assume the fire just stays lit, the mass of air within the CC would cause the pressure in the CC to rise enough to force air against it's natural path and out the FB intake. And, if we were to crack the chimney dampener just "enough"....... Wait, is that what a "backdraft" is? And a backdraft only lasts until the pressure in the CC, "behind" the fire, drops below the amount of pressure in the fb.

so, a backdraft as I think of it, like in a house fire anyway, (please correct me if i'm wrong cuz I'm no firefighter...) is when you have a rip roaring fire going and close off the exhaust or the place the fire is exiting the structure, but the fire still has an air supply feeding it, the space will pressurize until there is no where else to go and you will have a superheated air mass that is now highly pressurized and also contains gassified particles so much that it finally becomes explosive then for a period of time overcomes the original path and relieves the pressure backwards? in the case of a smoker you wouldn't necessarily have a big enough fire to cause the explosion but you would see the smoke and products of combustion and heated air mass try to come out through the air inlets and also the doors would start leaking. until the fire is finally quenched by lack of oxygen. I would say your statement is correct.

So only if the above is correct, do you mind moving on to step 2? Which would be how the ratios and openings effect the chimney effect. Actually I think I can deduce it, however I don't know what the ideal smoker flow would be. .5?

Sent from my Moto Z (2) using Tapatalk

so, I've never actually measured the pressure in each area of the smoker... would like to do that tho... but as much as I mess with air balancing and air movement (my other full time job/ life) I would say that a half inch of water column is very close.
so in a reverse flow we design the air inlets big enough so that in the worst case scenario when trying to get a good bed of coals and the temperature of the smoker "up to temp" we will have adequate air available for combustion.
the throat opening is designed to not restrict the airmass at the cook chamber so we move the total amount of heat from the heated airmass to the inside of the space to be heated... the cook chamber.
the space under the baffle plate must be equal to or slightly greater than the throat opening so we do not restrict there either. if it is too big then the velocity of the airmass would get to be too slow which would directly effect convection in the cook chamber.
now at the baffleplate gap, we need to cause just the right amount of restriction to hold the volume of heated air just long enough to heat the baffle plate evenly so that we get an even amount of radiant heat across the cook chamber.
now that the baffleplate gap adds restriction, the air mass picks up velocity and starts to cool off slightly, since the baffle plate absorbed heat from it...
now we have the radiant heat from the baffle plate and the heated air mass moving through the cook chamber and winding around the objects in the cook chamber randomly. the moving air and the radiant heat all works together more evenly in the cook chamber giving us a more consistent product.
If we keep the stack even with the top of the cook chamber, the stack damper all the way open, and the proper length then we will have the correct air flow and velocity established to prevent condensation in the air mass collecting in the smoke stack and also will have proper combustion.... thin blue smoke.
If you close the damper of restrict combustion air supply to the firebox then it will directly effect proper combustion and could cause the coal bed to go out etc.
only time I close down or completely shut the smoke stack damper is when I need to drop the cook chamber temp or quench the fire.
I only use 2 methods to control cook chamber temps...
control the size of my coal bed... fuel
open and shut air inlet dampers to supply more or less air for combustion.


Holy crap.... Hope I said it right!

[A_Stubbed_Toe]

I definitely came to the right place! I can't thank you enough for letting me pick your brains. When you say that the area underneath the baffle plate needs to be the same size or slightly larger than the throat opening, does a shadow plate not significantly enough slow down the rate of speed of the draft? How does the fluid (heat, smoke, and byproducts of combustion) travel once it reaches the end of the shadow plate? Could you theoretically make a "center feed" smoke out of a horizontal offset design but at the end of the shadow plate tack a piece of angle that sticks out facing the bottom of the smoker, leaving two equal sized gaps at the ends of the baffle plate? ( then placing exhaust at the center of the CC)

I am picturing it much like an eddy in a river where there is a rock or sudden squeeze in the river followed by an opening on the back side of it. I understand that you would have to somehow shield the amount of heat nearest the FB, but in this instance a ceramic refractory would do the trick, I think..........tweaking the size of the angle iron would be the difficult variable.

I am planning on insulating the firebox and I believe ceramic insulation and a ceramic refractory coating, something like https://shop.clay-planet.com/itc-100-ht ... ating.aspx should be more than enough to justify using an interior FB thickness less than 1/4." I think it would be also incredibly unique to make a smoker than is finished out in wood, have a bit of Ipe laying around which would be perfect. I just worry about the heat transfer from the standoffs to attach the wood. Thoughts?

Sorry to get off topic but I didn't want to start a new thread since I seem to have your attention here.

[Frank_Cox]

I definitely came to the right place! I can't thank you enough for letting me pick your brains. When you say that the area underneath the baffle plate needs to be the same size or slightly larger than the throat opening, does a shadow plate not significantly enough slow down the rate of speed of the draft?

a shadow plate is what we refer to as the plate under the baffle plate. so on a centerfeed reverseflow the throat opening is directly under the center of the baffle plate. this would make an intense hot spot in that place. a shadow plate would be directly over the throat opening and 1 inch or so below the baffle plate. so in this case I don't know if I understand the question. If you were speaking of the underside of the baffleplate then we would call that "friction loss" in this situation it is minimal but a good compensation for that is why we keep the baffle plate at least the same height as the throat opening or slightly above it. this way the restriction is at the opposite end of the baffle plate.

How does the fluid (heat, smoke, and byproducts of combustion) travel once it reaches the end of the shadow plate? Could you theoretically make a "center feed" smoke out of a horizontal offset design but at the end of the shadow plate tack a piece of angle that sticks out facing the bottom of the smoker, leaving two equal sized gaps at the ends of the baffle plate? ( then placing exhaust at the center of the CC)

perty much... the firebox would need to be in the center of the cook chamber directly underneath. then divide the throat opening SQ inches between both open ends of the shadow plate and keep the shadow plate 1 inch below the bottom of the baffle plate. one more thing to consider is making the shadow plate 2 inches or so bigger than the opening of the throat.
if you attempted this design with the firebox at one end then you would need to do some serious math or make a really good guess to get the gaps at each end tuned correctly. the one closest to the firebox would be much smaller. but then it would be better to just do a regular reverse flow and get it over with.

I am picturing it much like an eddy in a river where there is a rock or sudden squeeze in the river followed by an opening on the back side of it. I understand that you would have to somehow shield the amount of heat nearest the FB, but in this instance a ceramic refractory would do the trick, I think..........tweaking the size of the angle iron would be the difficult variable.

right, if I'm understanding your statement, you would be better off with a standard reverseflow or move the firebox to the center of the cook chamber.

I am planning on insulating the firebox and I believe ceramic insulation and a ceramic refractory coating, something like https://shop.clay-planet.com/itc-100-ht ... ating.aspx should be more than enough to justify using an interior FB thickness less than 1/4." I think it would be also incredibly unique to make a smoker than is finished out in wood, have a bit of Ipe laying around which would be perfect. I just worry about the heat transfer from the standoffs to attach the wood. Thoughts?

Sorry to get off topic but I didn't want to start a new thread since I seem to have your attention here.

if you cut a square standoff and cut out the center of it so you minimize the heat transfer surface but still have a standoff it would work fine. so cut a squre with a smaller square hole in it maybe?

great conversation!

[Rodcrafter]

[The Czar]

Well you just got BTU’D!!!!


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[Dirtytires]

That was amazing...but to super over-simplify....air leaks are bad.