Intake styles?

[rikun]

Hi,

I'm currently building my first RF smoker out of 160 gallon tank. Everything has been sized pretty much by what the calculator said, my FB is going to be around 108% oversized and the throat is also a bit oversized.

I need to cut my FB plates soon. But I can't really decide on intake style, locations and number of them!

I've read that you'd want a lower and upper intake to fine-tune the combustion (Ribwizzard). Here's my plan, have a stab at it :)

The first picture is the side of my FB (both sides would be identical). There's a "texas slide" vent on both sides, under the fire level, together they're around 63 square inches which is a lot more than the 41.40 square inches the calculator calls for.

Is that a bad thing? I think it wouldn't matter, since you can always close down your intakes.



The second picture is the back of my firebox, there's a large pie vent centered on the door. It's above the fire level. This would be mainly to get more draft without increasing heat. Is it big enough compared to the other intakes (it's 30 square inches by itself), or should the upper- and lower intakes be roughly the same size?



I considered making all the vents pie vents since I have access to cnc plasma, but getting the pie vents under the fire grate level proved to be challenging...

My fire grate level is drawn about 6" off the bottom, is that ok?

 

[daveomak]

The upper air vent doesn't need to be over 10%-15% of the recommended total air intake....

Under the fire grate.... Ribwizzard put them on the bottom of the FB..... Check out his builds.....

 

[txsean]

lol the Texas slide... haven't heard that one. Here is what I am doing on mine though. I put one 4" x 7" intake on either side of my firebox with a sliding damper. This is nearly double what I need but like you said, you can always close them off, and I wanted the option to be able to close one side off if needed based on weather (crazy winds) They are located near the bottom of my box, below the fire grate.

sb5.jpg

• txsean
• Feb 4, 2014

sb3.jpg

• txsean
• Feb 4, 2014

 

[daveomak]

lol the Texas slide...


Isn't that a northern version of the 2 step....:biggrin:

 

[ribwizzard]

I think what you have drawn out would work fine, except I'm unsure what you mean by back of firebox. That upper pie vent looks to be a good height, but you want it placed on the firebox wall that would be directly across from your firebox to CC opening. And it does not have to be very big, your just letting a little fresh air flow into the flame portion of your fire. I'm concerned that some builders are attempting to locate them too high on the firebox and may experience draft problems. When I refer to " upper" vent, I mean " above fire grate level".

Picture it like this:
If you stacked logs into the firebox that would represent the amount of fuel that you think your average fire would consist of, then layed a straight edge with one end sitting on the bottom lip of the firebox to CC opening, and the center resting on the stack of logs representing your fire, the straight edge should be angled downward at the far end. Where it would hit the end wall of the firebox should be the HIGHEST point of the upper air vent opening. The taller the firebox, the more angle to the straight edge, and the air vent can be installed lower on the far wall, giving better draft.

 

[rikun]

Okay, that makes sense.

Based on that analogy, mine's probably still way too high. I don't really have a clue how many logs I would need, but I think it wouldn't be too high stack at all...

I know that Ribwizzard puts the lower went on bottom, but I don't really want hot ash falling through the vent while cooking. Unless I'd make an ash pan outside...

 

[ribwizzard]

Yep, you got to install an ash catch pan, nice thing is that the ashes don't build up inside the firebox, you don't have to open the firebox to empty ash pan, and your ash pan is not to hot to handle when you need to empty it. Oh yeah, best part is that it's self emptying at speeds over 25 mph!

See, there are reasons behind my madness!

 

[rikun]

Do you have a picture of your ash pan? I'm not sure how to incorporate it under the FB but still maintain a good flow of air from the vent.

 

[ribwizzard]

not handy, I bought a stainless steel drip pan from reteraunt depot for like $8.00 bucks or something like that, and will set approx 3 inches below firebox, in a rack, and will be removed before trailering. I'll weld a spring handle to it, and it has a nice heavy lip to hold it in place.

On other builds I have used simular pans, and on smaller 1/4 sheet aluminum baking pans as well. On #19, the firebox sat on top of the trailer, so I put a hole in the trailer deck and installed the pan right under the trailer. It worked very well and was hidden from sight but still easy to grab and empty.  This build will be lower to ground, so pan will have to be removed before going down the road.# inches of space is all thats needed to let the air flow good.

 

[sqwib]

20101219436.jpg

• sqwib
• Feb 14, 2014

I have three 2" holes in the back also with a sliding plate (never really needed it.

 

[rikun]

Thanks,

I think I'm going Ribwizzard's way ;)

Let's see how it goes, this is my first stick burner so I'm hoping the learning curve isn't too steep compared to "traditional" vents.

 

[ribwizzard]

See, here is the lower pie vent, them I will do two levels of slide vents on the door, one right above grate level, and one slightly less than mid way up.

image.jpg

• ribwizzard
• Feb 15, 2014

 

[ribwizzard]

I lined the bottom of the firebox with 1/4" plate , tapered down toward the vent so the ashes would not build up.

 

[rikun]

Is there a reason why the bottom vent is more towards the back of the firebox? Draft? I was sketching it dead middle on the bottom plate.

 

[ribwizzard]

It's closer to the door, away from the cook chamber, ....several reasons; easier access to ash pan, shorter swing on slide handle, keep center of fire away from back wall, and always burn " inward", easier to place starter chimney directly over vent if it's closer to door. Etc.etc.

After awhile, I just kind of start doing things to correct what I didn't like about the last one.

 

[rikun]

Well,

How's this looking? I lowered the fire grate level a lot, since I didn't need that extra space without the vents on the side.

This is the bottom of the FB. The 6 segment pie vent is about 75 square inches fully opened.



Here's the backside of the smoker (straight across from the FB to CC opening). It has two small pie vents on the door, around 4.8 square inches a piece. The first one is 0.7" higher than fire grate level (is that enough?), the second one is couple of inches down from the center.

 

[bigwheel]

Well to me a Texas style intake would be a clone of how Klose and Gator does it with the rectangular sliding louver system. I have the Texas style as in one of the pics..with the emblem of the Great State on it. Sorta air infused one side of the fire while the other side suffers. As a dedicated Klose owner explained one afternoon..the fire needs air all the way across from left to right..with as much intake above as below the fire. Meaning the louvers need to hit dead center of the fire grate. I do not know or want to know about the physics of Reverse Flow. Its crazier than offset cooking as far as I can tell. I also dont know what all those extra holes are for in the diagrams. Sorry. lol

 

[ribwizzard]

On your pie vent...#1, 3, and 5 triangle need to be smaller than the outlined segment, so as there is enough overlap to seal, also need to calculate how much your going to leave as an inner circle so you can install a bolt for a pivot point. I recommend at least a 1/2 bolt and go stainless, install a heavy spring on the bolt under the vent to keep it tight but give enough " give " so you can free it up if it gets stuck from sitting.

Here is my door vents I decided to go with...

image.jpg

• ribwizzard
• Feb 23, 2014

 

[ribwizzard]

I would have liked to spread the holes wider, but the way I built this firebox did not allow that.

 

[rikun]

Hmm yeah you're right about the overlap, I once thought about that but forgot about it :D

More Sketching to do then...