First build + vlog

[av8bdriver]

For those of you have have utilized an upward angled baffle, have you noticed that it requires a stack with an increased draft potential in order to have the same amount of pull as you would have without a baffle at all?

I was experimenting with some things using forced air through a simulated throat opening, which I understand is different from what happens with a stack and a fire, but I noticed an obvious increase in back pressure when using a baffle. Obviously the back pressure also increased as the baffle was positioned to become more parallel with the simulated throat opening while maintaining the same maximum distance with it.

The goal of the experiment was to see if I could place an obstacle in front of the throat that would yeild similar results to what the Franklin smoker claims it achieves with the bimetal shelf above the throat. If you not familiar with the claim, they basically say the bimetallic shelf bends from the heat and creates a swirling of air in the cook chamber; Scattering the smoke and aiding in convection.

Hey there... I just finished my pit referencing Dave's throat/baffle design. CC 60X24X3/8", FB 24X24X3/8". I definitely have some back pressure associated with what I think is the baffle design. My baffle is a little different from Dave's, in that mine is completely vertical and in front of the throat. Mine also forces air up to the top. I get amazingly even temps along the bottom grate. The top grate sees 100deg hotter by the FB and middle, and 50deg by the stack. This gives me options and I do love it. But when I open my top FB dampers to what my calculations call for, smoke comes out of the holes. My stack is 5" pipe, 36" above the cook chamber. I'm still learning this pit, only 3 cooks so far. I'm not sure if a taller/shorter stack would solve the issue. Don't really plan on making changes at this point bc it cooks so well. Probably just not gonna run quite as efficient as it could. Still makes amazing BBQ! Good luck! This forum has done wonders for me. Thanks to everyone btw!

[ThinBlue]

Thanks for that response av8bdriver. I was beginning to think I was never going to get any feedback on that question.

[ThinBlue]

I'm having a heck of a time finding a 6" pipe for my stack on the salvage market. I did find some 8.5" O.D., not sure exactly what the I.D. is on it. Would it present any issues if I were to use that large of a pipe for my stack and still have it be 2-3ft above the cook chamber so that the smoke is exhausting above the eyes? For reference, if I make the assumption that the I.D. is right at 8" the calculator tells me a stack height of 8.5". I do intend to put a damper on the stack.

[Dirtytires]

You can use any diameter you want but still need to follow the stack volume as given in the calculator I order to have a properly tuned pit. So, in this case, an 8" diameter pipe needs to be 8.5" high.

[Back9Q]

You can definitely go to narrow on ID but a lot of leeway going larger. 8” is fine and you dont need to only do 8.5”. Remember calculators are starting point. You can easily go 36” on that stack if you wanted to.

Some say that are will cool if too long but I have never seen that to be case on a reasonably length stack. Metal/air will be hot enough to prevent this from happening. I added a 6ft duct extension on my current offset to test and air temp stayed close to CC temp.

I wouldnt go over 8” just from appearance factor on backyard model but go ahead and make it desired height

Edit: look at Franklin Pit. Assuming his stack is 6” with his CC 42” calculator would have his stack at 13-23” depending on diameter. That stack is well over 3ft and his pits have some of best airflow out there

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[ThinBlue]

I love the different points of view. I was inclined to follow the same belief as Back9Q for essentially the same reason as he stated. Seems to me that just about every big builder technically has an oversized stack based on the calculator which would mean that every $2k+ pit is built poorly. Although I have no experience with those pits I don't believe that to be true.

The caveat I will throw in here is that I live in Arizona which means the ambient air temperature is somewhere between good golly it's hot and Freddy Krueger's melted face. My understanding of the science is that as the ambient air temp and the air temp in the stack are closer together the draft potential decreases. Along with that I seem to recall friction playing somewhat of a role in this which was tied to I.D. of the stack and causes the system to draw less air.

Anyone care to weigh in on the science of it for me? I just don't want to shoot myself in the foot on this one.

[Back9Q]

There is definitely science behind it that I dont fully understand. Been to AZ many time to visit friends and yes it is hot but not 225f CC hot. The air temp leaving stack will likely be slightly leas than CC temp near exhaust opening. Worst case scenario you will still have 80-100 degree difference. And that is if your smoker sitting out in sun. You may have it closer to house or under cover which would help

Yea friction plays a lot into it but not the point where if you are off on your stack by a few inches its going to adjust CC temp drastically. Dont over think it. 8” stack with damper at height you want it to be. Then make sure your FB air inlet and FB to CC open fall in line and are there are no points for air to be restricted

After typing above I just noticed backline posted pic of their smoker on IG. Im guessing this is 24x52ish with an 8” stack. Using 150% volume on FB this would put stack length at 12”. What do you think length is in photo? 48”?





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[ThinBlue]

[hogaboomer]

This is what it says on Feldon's in the chimney section:

• A chimney that is too short may produce insufficient draft (drawing of air). A chimney that is too long may cause the air to cool before it exits, reducing effective draft and worse, dripping of exhaust materials onto food!
• Many horizontal smokers have an exhaust between 30-40 inches in length, but there is no hard and fast formula.

[av8bdriver]

Thanks for that response av8bdriver. I was beginning to think I was never going to get any feedback on that question.

you bet!

[ThinBlue]

I found some more information on the subject from another forum. It had a scientific explanation that I admit that I haven't fully wrapped my head around but that's ok because there is some quick and dirty takeaways from it and I believe that's all that's really needed.

1) As stack diameter increases the flow rate also increases even if the overall stack volume is the same as a smaller diameter but longer stack. (Example: a 100 gal CC with a 3" x 6' stack will have the same volume as a 4" x 3.4' stack but the 4" stack will have a 2.75x higher flow rate.)

2) The larger the diameter of the stack, the less the stack diameter will apply friction to the flow rate, hence the increased flow rate. But, over a certain diameter there is essentially no friction impeding the flow rate and there will be no additional increases in flow rate by sizing up further. In this case the pipe wall is no longer providing any dampening and will rely solely on a mechanical dampener for controlling the flow rate.

The thread I'm referencing goes back and forth on and off the rails as members squabble a bit about who's right or wrong but my overall takeaway from the science is this:

Size your stack at a MINIMUM of 4" and make it as tall as you like as long as it looks good to you and is at least as tall as the calculator recommendation. The bigger the diameter the more draw you will have but also the more that you will need to rely on your damper to find your sweet spot. Once you go over say 6" you have likely achieved maximum potential flow rate unless you have a 250+ gallon smoker and will soley rely on your damper control prowess to achieve optimal draft. My own assumption from here is that the larger the diameter is past the point of maximum flow rate, the better the "resolution" you will have when make adjustments with your damper.

The over simplification:
Go "big", put a damper on it, and make it as tall as you want to make it look "right".

Eh? Sound about right guys, or does this somehow contradict your real-life experience?

[Back9Q]

Way too much science for me but yes I agree with min 4” and go up based on appearance and size of pit. The whole too long lets air cool is ridiculous. I would like everyone put a 10’ extension on their smoke stack and measure air temp coming out. Its still very hot and no way cool enough to cause issue IMO

With that said go as tall as you like


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[ThinBlue]

Here's the latest: https://youtu.be/7kVus_c5kh0

[Brewmaster]

Good video, keep 'em coming!

Like you, I'm in the large stack/large firebox camp since most builders seem to be going that way. I once ran different pit builders' numbers through the calculators and found most of their stacks were ~ 6" or so longer than the calculators recommended (rather than "a lot" longer) Either way best of luck with your build, can't wait to see some food coming out of that sucker!

Cheers

[ThinBlue]

can't wait to see some food coming out of that sucker!

Cheers

Thanks man.

Yeah you and me both. My wife has been stocking up on meat whenever she sees a decent price on something and it just makes me that much more hungry. I'm still cooking on my WSM in the meantime just to get it out of my system and so I don't go crazy. Although it might be too late for that. I've been trying to up my grill game as well since that is so much less time consuming than smoking.

[ThinBlue]

I'm so happy to start seeing some progress on this. We got the base all framed up and on wheels.

Check it out the progress, if you'd like: https://youtu.be/s5kfRcZ0v9Q

[Olibinoui]

Keep the good work! Its fun for you that you can work outside
on your smoker project. Here’s its winter with -20 -30 celsius so i work in the garage

[ThinBlue]

Very different here in Arizona. The weather here has been what most places would consider spring time almost all winter this year. Just have to worry about the wind blowing through and messing welding process when it outdoors. If we were doing this in the summer it would be a rather uncomfortable project.

[ThinBlue]

I hit a little road block while working on the firebox and I am back to looking for some materials so I'm going to be shifting focus towards the cook chamber once I get back to it in the next couple weeks. I know I have a little bit of spring in my cook chamber door. What is the point at which you guys will try to jack and chain it back to perfection and what is acceptable to not worry about that and just put a gasket on?

Also, when putting on the gasket do you only need to shim the hinge side or do you shim all the way around the same amount?

Any brand or type preferences for gaskets for a cook chamber?

One last thing to note - if you ever come across salvage metal that has been powder coated and you don't want that powder coat on there, don't try to grind or burn it off. It smells horrid and is probably doing terrible things to your lungs. Instead just get yourself some KleanStrip Adhesive Remover, pour it out on your piece and spread it around nice and even and let it sit for about an hour. Comes up very easy with minimal effort.

[Brewmaster]

I hit a little road block while working on the firebox and I am back to looking for some materials so I'm going to be shifting focus towards the cook chamber once I get back to it in the next couple weeks. I know I have a little bit of spring in my cook chamber door. What is the point at which you guys will try to jack and chain it back to perfection and what is acceptable to not worry about that and just put a gasket on?

We try to get them straightened out without thought of using gaskets, and keep at it until the fit is close enough. None of them are perfectly tight-fitting in my experience, I mean perhaps as much as 1/16" gap here or there on the chamber door fitment. Some smoke may leak out the tiniest bit when starting the fire, but soon as the draft is established there are no longer micro smoke-leaks.

Also, when putting on the gasket do you only need to shim the hinge side or do you shim all the way around the same amount?

Any brand or type preferences for gaskets for a cook chamber?

If I were fixing poor fitment with gasket I'd use something highly compressible, possibly a high temp foam type gasket. I'd first cut the hinges off, apply the gasket and set the door in place, apply pressure to the door or wait a few days to allow the weight to compress the gasket, then weld the hinges back on. Beyond that what I've done on a few cookers is to use Ultra Copper silicone and plastic food wrap. Do a super clean on the area to apply gasket, apply a good thick bead of the copper silicone, with the area around the door opening totally covered/laminated with plastic food wrap, promptly close the door/silicone gasket onto the food wrap. This will allow a ton of squeeze-out and a good seal all the way around in both thick and thin areas. Let it cure a solid 2 days before opening the door, remove the plastic food wrap, and trim away any access squeeze-out with a utility knife. Ultra Copper is rated to 700 F and I've never seen it fail on an offset cook chamber, the firebox is a completely different story

Oddly, I don't have any decent photos of the process, other than that one time I tried it on a firebox (along with the chamber door)

Good luck brother!

[Dirtytires]

I like to use 0.25 inch thick, self stick, felt gaskets from lava rock. As long as you clean the metal properly, the gasket will stick great....I've got over 8 years on mine. With that in mind, you need to keep the gaps to less than 0.125 inch. If your gaps are bigger, you need to use a thicker gasket as most are designed to compress about half their thickness.

Yes, you have to put the gasket all all four sides. To keep the hinge from binding, shim the door exactly half the thickness of your gasket all around and then weld your hinges on. This will give you a "crush" clearance for the gasket and keep the door from binding when closed.

[Iwishicouldcook41]

Subscribed to channel and thread. Looking forward to progress. Mind if I ask what design software you’re using for those renderings?


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[ThinBlue]

Subscribed to channel and thread. Looking forward to progress. Mind if I ask what design software you’re using for those renderings?


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Thanks for all of that. I hope you enjoy!

The program I'm using is Adobe Illustrator, but any vector based drawing program can do the same thing. I believe there is a couple of free ones out there that should be acceptable for simple stuff like that. You could also use Microsoft Word, if you already have access to that, and utilize the shapes drawing options (Google docs might work too). If you do that you'll want to come up with a sizing ratio (scale) since you can't make a document large enough to accommodate the actual size of your smoker. So for example, 1 foot in the real world might equal 1 inch in MS Word or whatever works for you.

A lot of folks will use 3D rendering software like SketchUp, and I can use it as well, but I'm not nearly as proficient. I think the learning curve is a little steeper with 3D rendering softwares. It's worth it though if you are type type that likes to dabble and learn new things and want the best representation of whatever you're looking to model/design. The rendered results are much more impressive with 3D vs vector.

As you can see, there's more than one way to skin a cat. I should mention that good old fashion graph paper and a ruler works too.

[ThinBlue]

Sharing a few progress pictures. With the FB on pause we started working on the CC last weekend. Cleaning the inside of that thing was a 5 hour job just to get it to where it is now. I hit it with a wire wheel to knock to the crusty rusty surface and then started taking a zirc wheel to it. I got the gnarly weld going all the way around the CC smoothed as much as I could. We are still deciding if we want to go back over it with some welds and grind it back down again to get a smooth surface or just leave it gnarly and "textured". On the FB we tacked the door on to try to minimize any warping that might happen when we cut out the door out on that. Hopefully between now and two weeks from now when we reconvene I will find the materials I need to finish what I want to do with the FB.

[Dirtytires]

Looks great but 5 hours with a grinder is more than I have patience for. I would have hauled it off the media-blast shop and happily skipped the sore arms, ringing ears and numb fingers.

Of course, I have gotten wiser as I've gotten older and probably would have been guilty the same at one time or another. It does look good, tho. Keep in mind that it does not need to look showroom quality and the imperfections add character. A good trick when deciding if the work of rewelding and regrinding is worth it is to hit it with a quick coat of black spray paint. It's amazing how imperfections blend away when it is all one color and often I just leave it alone.