Building Horizontal Gravity Feed

[Texasbowhunter]

I have been contemplating a Horizontal Gravity Feed unit to see if it could be done successfully
I thought I would reach out to you guys that has more understanding then I on things I should consider when fabricating this Unit and would like to get some feed back from you...
I'm visualizing a round unit and the unit being insulated...Trying to get the door and tight as possible would seem to be a goal
The firebox would be insulated as well...
The thinking here is I'm going to keep as much of the Gravity Feed Vertical as possible
So if I use the BBQ calculator to determine the the size of heat opening to where it goes into the Cook Chamber based on the Cubic inches that the chamber is would this not suffice?
So if the opening of the heat where the fire is made to be sent into the CC was based on the size of the CC would it, per the calculations, do you think it would work?
So once I put the numbers in and got all the sizes required from the Calculator could I not just build a HGF unit and if not what would I need to also consider???
Also is there a reason that would be beneficial for the end of the CC to have that BOWL like a Propane tank has vs. a flat?
Thoughts on being a reverse flow vs. an offset...Pros and cons
I'm kind a new at Smoking so there may be allot of stupid questions asked since I have and only smoked on one style of Smoker and that is my Gravity Feed Vertical I finished a couple years back thanks to this forum and design...
I have a friend that built a offset smoker that has been insulated with 3" of insulation so I figure it may not be to over whelming but as mentioned above I'm kind of seeing the Gravity Feed Portion added...
I'm kind a seeing this project perhaps happening when the temperatures are cooler here in the south...It would also give me the opportunity to gather up as much of the bigger materials as possible from time to time...
I was kind a leaning towards something with a 24" CC and something perhaps in the neighborhood of 48"- 60" long with at least 2 racks but may entertain 3 racks if possible and your thoughts and feed back...
Thoughts on doing 1 door or 2 doors whether it be 48" or 60"...I'm thinking 2 doors so I don't loose to much of the heat and there fore should be able to build back up rapidly...Thoughts here on doors?
So lets start here for now and well discuss this before I continue on with more conversation on what to add and perhaps how to add...
Thanks
Paul
As an added bonus I'm cheap
So is there a FREE and EASY software I can down load to start the design of this project and if there isn't is there software out there that is EASY to use and and wont break the back and note EASY would be the keep word here...

[Pitmaster Big D]

I've been looking at the same thing. From what I have been told you will need around 100cfm of air flow. I have looked at some of the miron mixon gravity feeds and they have some that are similar and use 2 x 25 cfm blowers. I've have also looked at the "throw away" big box store ones trying to figure out how to replicate one that will hold up for a few years.

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[Texasbowhunter]

100 CFM of air flow??? Is this the air coming in to the fire pit? the ball valve? because I was considering using a forced fan to help with stoking and regulating the fire uniformly...but from time to time using the ball valve...
Would this not be based on the size of CC?
The actual square inches of firebox where all the magic is made vs. Cook Chamber is @1% of total CC
So working with a 24" round 60" long the CC volume is 27129
So logic would give a firebox where the magic(fire) is made should be 271.29 square inches...which could be around 18x3x5 = 270
or I figure out what the square inches are with a moon cut on the barrel just like making a offset and using those measurements to size my fire box area...
When I speak of Firebox area I speak of where the fire (magic) is sitting only...

[Texasbowhunter]

So I looked at the Myron Mixon Horizontal Gravity Feed Smokers and have a question...
First let me state this and again forgive me for not knowing the actual terminology needed to discuss this but I have heard there is a PLUS to having the round CC...Something about the way the Heat flows inside the CC as apposed to the a square or hard sided CC...
Thoughts
Is it really that much of a benefit to have the round CC over a square CC
Having the square or rectangular CC would certainly be an advantage in building as compared to the round CC
Thoughts

[tinspark]

Is it really that much of a benefit to have the round CC over a square CC
Having the square or rectangular CC would certainly be an advantage in building as compared to the round CC
Thoughts

My thoughts are that it prolly doesn't matter much round or square as far as circulation in a GF, especially since you are dealing with so little airflow..
On that note, 100 CFM (CFM= Cubic Feet Per Minute of airflow) and is way out of whack for a smoker of this size. Pete may be able to answer that question better though.. Unless someone is sizing a 6" round Air Conditioning duct (6" round at .1in. static pressure) lol!! I think it was a typo.

Once a GF heats up and produces smoke, it is pretty uniform and fills up with smoke fairly evenly throughout the cook chamber, at least mine seems to.
So a GF My only concern with a long round (horizontal) cylinder as you are describing is the transfer tube. It will be very long. It also acts as a heat sink. And since it is not closed like a traditional RF smoker which forces the hot air and smoke along the bottom course of the cooker, which also heats the BP evenly and is what a lot of pitmasters here like about theirs. With a super long channel open bottom channel (aka transfer tube TT) the smoke follows the course of least resistance, which may exit the tube and never heat the far end of the TT and may give cold a cold spot at the far end of teh cooker.. Truth be told, I have never seen one like you want to build, but that is what came to my mind when you were describing what you want to build. I think that you may be able to control the heat better if you go vertical gravity feed with the traditional transfer tube.

[Pitmaster Big D]

The 100cfm for blowers was not a mistake. I have been talking about one if these with Frank for a while and that was the number he came up with. I was looking at a 24"x48" tube with a gravity feed shot on the side. The BBQ Guru controller kit that is recommended for the second to largest Myron Mixon one uses 2 x 25cfm fans and the largest uses a special fan box that I have not been able to get a good look at. It has something to do with the fact that it is horizontal and not vertical. With the vertical cook chamber the heat/air has less to travel across, and natural heat rising helps the process so you can run off of just a ball valve. With a vertical it needs the extra air flow.
I'll try to tag frank and see if he can jump in with some additional info.

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[tinspark]

The 100cfm for blowers was not a mistake. I have been talking about one if these with Frank for a while and that was the number he came up with. I was looking at a 24"x48" tube with a gravity feed shot on the side. The BBQ Guru controller kit that is recommended for the second to largest Myron Mixon one uses 2 x 25cfm fans and the largest uses a special fan box that I have not been able to get a good look at. It has something to do with the fact that it is horizontal and not vertical. With the vertical cook chamber the heat/air has less to travel across, and natural heat rising helps the process so you can run off of just a ball valve. With a vertical it needs the extra air flow.
I'll try to tag frank and see if he can jump in with some additional info.

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Wow sounds interesting. Must need a lot more air through it for some reason. A typical GF without a blower and a 2" ball valve will only pull approx 10 -15 cfm I am guessing through that small of an opening. My flameboss max's out at 21 CFM at 100%. It usually runs about 15% (less than 4 CFM) which keeps me at about 225 degrees. If I were to run it wide open, my smoker would likely spike at over 500 degrees. I wonder why a horizontal that small would need 1000 cfm? Man if it doesn't work you can always turn it into a forge... LOL!! post some pics when you get that thing going.

What would be cool is to run a BP along the bottom like a regular RF smoker and attach the GF section to the side. Maybe that is what he is talking about. That'd actually be pretty awesome . but the 100 cfm still has my head scratching a bit, unless it were a 500 gallon tank or something..

Yeah please give more info on this when you find out..

[Pitmaster Big D]

The 100cfm for blowers was not a mistake. I have been talking about one if these with Frank for a while and that was the number he came up with. I was looking at a 24"x48" tube with a gravity feed shot on the side. The BBQ Guru controller kit that is recommended for the second to largest Myron Mixon one uses 2 x 25cfm fans and the largest uses a special fan box that I have not been able to get a good look at. It has something to do with the fact that it is horizontal and not vertical. With the vertical cook chamber the heat/air has less to travel across, and natural heat rising helps the process so you can run off of just a ball valve. With a vertical it needs the extra air flow.
I'll try to tag frank and see if he can jump in with some additional info.

Sent from my SM-G998U using Tapatalk

Wow sounds interesting. Must need a lot more air through it for some reason. A typical GF without a blower and a 2" ball valve will only pull approx 10 -15 cfm I am guessing through that small of an opening. My flameboss max's out at 21 CFM at 100%. It usually runs about 15% (less than 4 CFM) which keeps me at about 225 degrees. If I were to run it wide open, my smoker would likely spike at over 500 degrees. I wonder why a horizontal that small would need 1000 cfm? Man if it doesn't work you can always turn it into a forge... LOL!! post some pics when you get that thing going.

What would be cool is to run a BP along the bottom like a regular RF smoker and attach the GF section to the side. Maybe that is what he is talking about. That'd actually be pretty awesome . but the 100 cfm still has my head scratching a bit, unless it were a 500 gallon tank or something..

Yeah please give more info on this when you find out..

I agree. I'm still looking into it. It's definitely something I would like to try even as an experiment.

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[Big T]

It has been done before on the forum by another member. He built a 24X67 RF cooker and he built a removeable gravity chute that he could attach to the top of his FB. He ran it without any type of forced air control device and he said that it used about 50-60 lbs of charcoal to maintain 250 degrees for about 10-11 hours. I'll post a link to his build so you can read the details but all of the pictures were lost when they updated the forum several years ago. It was a really neat looking pit. https://smokerbuilder.com/forums/viewto ... =11&t=3929

[tinspark]

It has been done before on the forum by another member. He built a 24X67 RF cooker and he built a removeable gravity chute that he could attach to the top of his FB. He ran it without any type of forced air control device and he said that it used about 50-60 lbs of charcoal to maintain 250 degrees for about 10-11 hours. I'll post a link to his build so you can read the details but all of the pictures were lost when they updated the forum several years ago. It was a really neat looking pit. https://smokerbuilder.com/forums/viewto ... =11&t=3929

That's a bunch of charcoal. that could add up quick $$. Especially if doing just for back yard enjoyment.
My stick burner is cheaper to run than my GF. I have been paying about $20 for 40 lbs. So that adds up to $30 for a 10-11 hour cook.
mucho denaro!! (big bucks) unless being done at a restaurant or catering service and built into the cost
I did 16 racks of ribs and 20 tritips on less than a 20 lb bag of charcoal ($7-$10 fuel cost) and a few chunks of oak in the ash pan for my sons graduation party last month.
Edit: I posted a few pics of this cook in my GF build thread on the last page...
https://smokerbuilder.com/forums/viewto ... 30#p114730
Edit: 14 trii tips not 20, but I think I had the room for the extra 6 (tight fit tho)

[Big T]

He said that he only used it as a GF a couple of times because of the fuel consumption. Stumps builds a 6' horizontal cabinet GF but it doesn't say what the burn rate on it is on his website.

[Frank_Cox]

Hey fellers!
Thanks first of all to PitmasterBigD for hollering at me about this post!
Been talking abou this for years ever since the thread that BigT mentioned earlier.
I remember meeting Terry... the guy that built it in person at the wildwood bash in st louis years ago.
he said it was a fuel hog.
He swung by the shop a year ago and we talked about it a little more. still the same results.
Now on his build the GF chute was mounted to the top of the firebox.
I believe this was the biggest part of the fuel usage issue.

So I'll talk a little on the 100 cfm number that bigd mentioned.
So for the best average number for wood to completely combust and taking into consideration moisture content of the wood and the different wood types, wood requires an average of 130 cfm per pound to get a clean thin blue smoke and also a good BTU capacity.

Since wood is not refined like charcoal it has a much lower BTU capacity per pound that charcoal which is a lot higher.

Now for a stickburner we require a lot more air flow to get complete combustion, but not all the air moving in the smoker is used for combustion...
since the fire is offset from the cooking chamber, we need a media of some kind to carry the heat and smoke produced by the fire to the cooking chamber.
kind of like a water heater. burning gas in the water heater then we carry the hot water to the rest of the house.

so for the amount of heat required to heat a horizontal cooking chamber we need enough air for complete combustion and also enough air to carry the heat from the firebox to the main cooking chamber.

this is why the firebox is sized as big as it is.

moving on to charcoal...
as tinspark said that much air would make a forge!

yep for real. since the gravity feed chute on Terry's offset was mounted in the firebox... offset from the main cooking chamber , it required a lot more air flow to carry the heat into the cooking chamber.

looking at some fluid dynamics related stuff- air is a fluid and has mass.
when it is heated it's mass per volume is also changed.

100 cfm of air sounds like a lot possibly but in an offset smoker it is not a lot at all.
100 cfm of air in a 6 inch round duct in your house feels like it is "blowing real good"
100 cfm of air in a 24 or 30 inch duct is barely enough to "feel" blowing.

this is because of the "cubic feet" per Minute. you have a lot more room for that 100 cfm to move through so velocity and pressure are a lot less.

20 cfm of air from a blower on a GF cooker would not even be noticeable over a 48 inch span in a 24 inch diameter cooking chamber.

there would not be enough air flowing to carry enough heat through the entire length of the cooking chamber.
matter of fact, 100 cfm might not even be enough.

charcoal requires very little air for combustion.
in the vertical cook chambers like insulated cabinets, the shorter length and vertical direction of flow and close-direct flow of air into the cooking chamber makes it much more efficient.

so what would be a good design for the GF Offsets?

1- keep the chute as close to direct into the cooking chamber as possible.
2- less direction changes for the air mass is best.
3- I recommend a centerfeed design with a transfer tube perpendicular to the throat opening. so the chute would be mounted back dead center of the cooking chamber.

Hope this helps!

[Texasbowhunter]

I have read and re-read to get a better understanding of what each of you were discussing...
So let me provide a bit here on the direction I was considering going...
1st off I was considering a reverse flow...Most all that has owned both seem to prefer the reverse flow over the conventional offset...

So let me ask "With the Offset smoker what type of heat source best describes?
With the Gravity Feed what type of heat source best describes it? Is this one referred to more of a direct source?
I thought I had read where this was talked about with the various types of heat and actual terminology for them...

So if we were to build a Reverse flow offset with a plate ran most of the length in the bottom to direct the flow of heat from the firebox to the CC and this plate was at a max from the bottom of the CC - 25% and welded on all 3 sides...How far from the end should the plate stop? The same amount as to the half moon hole I cut"...So just hypothetically if the half moon was 400 square inches should the distance at the end of the plate be the same? Hope that makes sense...

And if I was to design the size where the actual fire was at 1% of the total Square Inches of the CC would it be enough heat to do the job?
This is 1 of my concerns where I would hope if would be 100% fuel efficient...
It seems that when I plug the dimensions in the calculator the half moon hole isn't much bigger then what I had come up with on the 1% sized accordingly

Again Hypothetically if the half moon hole was going to be a total of 400 inches and 1% of the GF firebox was sized to the CC and those measurement's of the firebox was figured at 250 square inches should one increase the fire box to accommodate the 400
Now as described above if I was to use a 25CFM fan would it be adequate to do the job

I may be slow but my thoughts is, all I'm doing is laying the CC on its side and so theoretically it should work...If not lets start a discussion and design one with the thoughts for those of us that have tossed this design around one of us or several of us may take it on...

Also where should the bottom portion of the vent be located for both racks?
I was thinking a Angle cut and sit close to the lower rack with the upper portion of the angle cut helping to draw some of the heat towards the upper rack...Thoughts?
Lets design one
paul

[Pitmaster Big D]

The best place to start would be taking a look at the ones that are pre-made. Master built, chargriller, and myron mixon make some. Chargriler and master built are smaller but you might be able to get some dimensions and the amount of airflow they have to use. I'm pretty sure on Myron's they use a controller with 2 x 25cfm fans. I've drawn up some designs for a smaller one but none of them seem to scale very well. The chargriller size is about the biggest I can see working with just a single 25cfm fan.

Personally I'm wanting at trying to make one from a 24"x36" or 24"x48" pipe, but I have some more designing to do to try to get even heat distribution as well as have the cook chamber at the proper temp without using a ton of charcoal. On a regular gravity feed the entire cook chamber is insulated so once the chamber is up to temp there is not much heat lost, it just burning fuel to maintain.
Adding a gravity feed chute to a standard reverse flow without insulation would require the fan to constantly be running to keep the temp accurate.

I really want it to work also. If I can come up with a design I'll share it.

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[Texasbowhunter]

Pitmaster D
Thanks for the reply
I understand the same as to insulated vs non insulated...My design and game plan forming in my mind is it will be insulated both the CC and the firebox just like the Vertical GF
As we all know with the building of our own Gravity Feed Smoker there is allot of work and cost so getting the Firebox sized appropriately when fabricating would seem to be the biggest hurdle...But lets not forget the OVAL Design since the thoughts were going to be a Reverse Flow Design...
Paul

[Dirtytires]

There is a calculator on the front page of the forum. You plug in your cook chamber size and it will help you find the proper dimensions for the firebox, throat, gap, chimney and air intakes. The calculator is well tested and will result in a well tuned pit if you follow it.

Another thought is to look for a set of plans from Frank. He has quite the selection and you can be certain the pit will operate properly. As a bonus, Frank is available for consultation during your build.

My reverse flow thrives on log splits. I had a small offset that was too erratic on logs that I could only use lump charcoal but I imagine that was due to the size of the pit. The bigger offsets you see on this site will run wood splits just fine.

[Pitmaster Big D]

There is a calculator on the front page of the forum. You plug in your cook chamber size and it will help you find the proper dimensions for the firebox, throat, gap, chimney and air intakes. The calculator is well tested and will result in a well tuned pit if you follow it.

Another thought is to look for a set of plans from Frank. He has quite the selection and you can be certain the pit will operate properly. As a bonus, Frank is available for consultation during your build.

My reverse flow thrives on log splits. I had a small offset that was too erratic on logs that I could only use lump charcoal but I imagine that was due to the size of the pit. The bigger offsets you see on this site will run wood splits just fine.

I've talked to Frank and Tom about this design quite a bit and some of the logistics are still not there quite yet. Smokerbuilder had tons of plans and some very great ones for traditional offset and standard gravity feed, but not a hybrid.

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[Dirtytires]

It sounds like you may be doing a lot of experimentation then....sorry I couldn't help.