The Texas BBQ Forum

Looks really good! Wish mine was that near completed. But, I am determined to finish my chuck wagon box before starting on the UBS.
I have the barrel, but am finding the lid like I want is hard to come by. The lid to my barrel was cut out with a chisel. I attached a strap of metal 4 inches wide and longer than the barrel diameter in order to keep it from falling in the barrel. I am thinking that the crack between the lid and the barrel may be all the exhaust I need and maybe more. What do you all think.
Anyway, I am close to finishing my chuck box.
Stan41

Hey Stan,

How much gap around the lid are ya talking? As long as it ain't too big, I think you thould be OK. Pictures would help!

James.

Not much gap, just what was taken out with the chisel. I'll try to get a picture of it tomorrow. Getting dark now.
Thanks,
Stan

Well, I've collected the supplies for a drum. Grates, steel, pipe, the works. Right now, my plan is 4-3/4" intakes and 2-1 1/2" exhausts. I want to be able to hit ~350°, so I need the intake. I'm wondering if I went a little overboard with the exhausts, though. I could just use 1 and have exhaust=intake. Right now, it's a 2-1 ratio.

Any thoughts from the experienced drumheads out there?

Rob, maybe I'm reading and not understanding this right. But 4 x 3/4" = 3" and 2 x 1 1/2" = 3", so that is the same, not a 2 to 1 ratio. I would have at least the same or more exhaust available to get more flow.JMHO
Having more intake is good, but if it doesn't have enough exhaust you won't get any more draw. the air flow is what makes the temp rise. if you don't have enough exhaust to draw the air in the intakes the fire can't burn hotter because it won't be getting any extra air. Example-- 3" of intake & 1 1/2" exhaust--even though you have more intake size you will still only be drawing the equivalent of the 1 1/2" exhaust. You can only draw in the amount of air that is equal to the amount of air you can exhaust or less if you cut the intake flow.

It's been my experience that more exhaust than intake is a good thing.

James.

I spent yesterday burning off the old paint, brushing off any rust ( inside & out ), and giving it a couple coats of paint on the outside. I was looking for something in the back of the shop when I found a couple left-over things from a commercial kitchen job we did last year and the light went on so I reworked them a little and we'll see if they work today. I got to quit digging around in the shelves back there. Hopefully I'll have it all together today.

Can't wait to see it!

OSD wrote:Rob, maybe I'm reading and not understanding this right. But 4 x 3/4" = 3" and 2 x 1 1/2" = 3", so that is the same, not a 2 to 1 ratio. I would have at least the same or more exhaust available to get more flow.JMHO

It's a number thing. A 2" line is twice as long as a 1" line. But area, OTOH, is length x width. A square 1" by 1" would be 1 square inch (1"x1"=1). A square 2" x 2" would be 4 square inches (2"x2"=4), or 4 times as big.

As for more exhaust than intake, that's always been my plan. My concern is having so much exhaust that the meat only cooks from the bottom, 'cause all the heat is flowing out of the top.

Ah, we'll see. I could be overthinking the whole thing. Wouldn't be the first time.

I understand the numbers thing, I did state it wrong. No symbols on the keyboard so, the area of a circle would be Pie ( 3.14 ) X Radius ( of circle ) X Radius. Pie R squared.
You could always cut back on the flow by closing off part of the exhaust.
Ok, here's one for the brain, if you put in a 90* bend in the pipe, like using a street elbow when using a raised intake, how will it affect the flow of air. Flow and pressure are both affected, it will actually take more exhaust to create the same flow of air as not having the 90* bend. It takes as much pressure to push a volume of air or liquid through a 90* bend as it does to push the same volume through a 20ft straight pipe. Thus, either more intake pressure ( fan or pump ) or more exhaust to pull the air. Many years ago I worked in a plant with tons of piping and we had to figure how much pressure to pump things thru the different runs of pipe. I don't remember the exact formula any more but that is the general rule of thumb.

Thanks for the help, Jim.

I'm planning on 90° elbows at the exhaust. Not for flow reasons, just for looks and protection from rain.

I think what I'll do is put both exhausts near the center of the lid. Then, if I need to, I can cap one pipe for smoking and not jack up airflow direction too much. Or, I could use a reducing cap.

Yep, *definitely* overthinking this thing.

Just some thought here. The area of a 3/4" pipe is .44sq in and the area of a 1.5 in pipe is 7.07 sq in. or about 16 times larger. Knowing that the air will combine with the carbon in combustion yielding carbon dioxide and with the resulting heat greatly expand the intake to exhaust ratio will necessarily be large but I don't know that number (air is mostly nitrogen but it does not expand as much when heated) . Also the exhaust will need to be open ( non-restrictive ) enough to support the proper convection flow for the intake. I guess that it should be easy enough to eyeball a good working example to get that ratio.

TX Sandman wrote:Thanks for the help, Jim.

I'm planning on 90° elbows at the exhaust. Not for flow reasons, just for looks and protection from rain.

I think what I'll do is put both exhausts near the center of the lid. Then, if I need to, I can cap one pipe for smoking and not jack up airflow direction too much. Or, I could use a reducing cap.

Yep, *definitely* overthinking this thing.

I think that the elbow not only is a good idea for rain but also for windy conditions where it might be favorable to "point" the exhaust by turning the lid.

Papa Tom
Outlaw


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Just some thought here. The area of a 3/4" pipe is .44sq in and the area of a 1.5 in pipe is 7.07 sq in. or about 16 times larger. Knowing that the air will combine with the carbon in combustion yielding carbon dioxide and with the resulting heat greatly expand the intake to exhaust ratio will necessarily be large but I don't know that number (air is mostly nitrogen but it does not expand as much when heated) . Also the exhaust will need to be open ( non-restrictive ) enough to support the proper convection flow for the intake. I guess that it should be easy enough to eyeball a good working example to get that ratio._________________

OK - that is way beyond me -- LOL

But - I do have more exhaust than intake. I have my exhaust holes located around the outside of the lid. My thought is that the heat from the firebox will rise, and be forced to expand and escape out of the farthest points. This, hopefully, will equalize the temps inside the drum. I have placed a thermometer on the grate, and found that my middle temp and the temp on my mounted themometer only differ about 20 degrees. I have not checked it using the Weber lid.

PT, you are right on the 3/4" pipe, but you used the diameter instead of the radius on the 1 1/2" pipe, it should be 3.14 x .75 x .75 = 1.76 sq in.
OK, let's just get back to building some smokers. All this math is giving me a headache.

Well the paint dried overnight, so I put everything together this morning except for I still have to build a platform with some steel wheels for the drum to sit on. Since it is going to be on concrete, I think small steel casters will work fine.
The wife made a smart comment so just to fix her I painted a couple things different. She didn't like all black, so I painted the air intake blue for cold air and the exhaust red for hot air. That ought to shut her up.


The blue intake


2 eyelets to run the remote temp wires thru-no sharp edges this way to rub a wire


Found a Spicewine temp gauge on the shelf. Added it to give it some class.


Looking inside, charcoal basket in the bottom, first pic with 1 cooking grate in, second pic both cooking grates in. There is a third set of supports under the lower grate to hold another grate which I may experiment with using a clay pan or some type of heat diffuser to sit on it.


Here she is with her red exhaust.
These are the stainless lid covers I found on the back shelf in the shop. I modified them and the and the hang down shelf so I could use them on the drum. The shelves are 11" X 15"


With the Nu-Temp units on their shelf. Could use it for other tings too.


A little better pic of the wiring and remote units on the shelf.

So, I better get this thing fired up over the weekend and give it a trial run.