Airflow is airflow (Is this true?)

stemc33 · January 2015

I often read about airflow is airflow in reference to temp control. Is this really true? What is optimum? Any fire science guys on the forum?

Sometimes my egg rocks along with tiny openings in the vents and sometimes it requires big openings. I'm not one to light my fire with the exact same OCD process that some of you do with every lighting, so I often get different results. What I do know is that I have left my bottom vent about half open a few times and the fire snuffed out by just using the ceramic cap. I realize that it probably took longer than if I closed it, but it proves airflow is not airflow. Intake and exhaust must occur. I know my coal stove always acts differently depending on outside temp and barometric pressure. If it's above 50° outside, I need to run it hot to keep enough draft going up the chimney to keep the house from filling with smoke. Just seems like so many variables when it comes to fire and am hoping one of you Eggheads is an arsonist or a Fire Marshall and can explain the science of fire.

Also, are EggHeads telling the truth about certain vent settings always produce the same results? I've gotten much better since switching to OO, but I still have an occasional fire issue.

SmokeyPitt · January 2015

IMO there will always be some variance because small pieces of lump/ash can block the air flow. I have a setting that I know "should be" about 350, but some days at that setting the egg will seem locked in at 225 degrees. The high-Q grate definitely helps but even with the high-q I still experience this from time to time. So, I open the vents to what "should be" 500 to get to 350. What I have found is that the clog usually clears itself and the temp will jump up. If I'm in a hurry I will sort of force the egg to the temp I want and keep an eye on it. If I'm not in a hurry, I set it to the "should be" vent settings and usually it will eventually reach that temp.

fishlessman · January 2015

ive never paid much attention to all the vent setting advice, i just open and close til the temps narrowed in close enough. lump burns easily unlike coal though, i dont burn coal until i get three days in a row under 50 degrees. no problem with coal burning right now though, my pile is disappearing quicker than i want

ive burnt 2 tons so far in the little camp

gdenby · January 2015

Temp control is all about air flow, and in my experience, the external temperature doesn't make much difference. If an Egg has been sitting in cold and damp, it may take longer to come to a desired temp, and in warm weather, somewhat quicker, but the vent settings are pretty much the same.

The vent settings are approximate, and seem to vary slightly depending on the size of the Egg. For instance, for a long low and slow, I know the bottom vent will only be about 1/8" open. As the meat heats up and shrinks, I may need to close the vent down to a 1/16th to keep the temp from rising. If the lump is running low, or getting ash covered, I may need to open to 1/4".

But don't fuss too much. Anything within 15F either way of a desired dome temp has negligible effect on the results. FWIW, most home ovens do not keep a specified temperature as steady as an Egg. Depeding on the sensitivity of the interior thermometer, how air tight the stove is, etc, a on oven may be running up and down around the temp setting way more than an Egg with a particular airflow.

hondabbq · January 2015

In one of my earliest post I mentioned this phenomena. The vent settings depending on season, temp, humidity, IN MY EXPERIENCE have an effect.

Of course wind speed has a major effect for me, as I am not sheltered from the wind like some. It can be calm or windy when I start the cook and will need to be changed sometimes if the wind dies or comes up.

Again IN MY EXPERIENCE, someone's vent settings in Texas will be different than mine up in Central Canada. I remember a post that someone never has their DFMT on and only adjust with his loser vent. I cant get below 350 that way.

In either case I am a firm believer that weather and climate have an impact day to day on the settings of the egg.

lousubcap · January 2015

As mentioned above, you have to have fuel, air (oxygen) and a heat/ignition source to get fire. Once the fuel is burning you do need air-flow (intake and exhaust) or you will eventually starve the fire of air(oxygen) and the fire will go out. Regarding settings for temperature control, there are many variables that go into the quantity of air-flow needed to maintain a certain temperature (+/- 15 *F close enough). FWIW-

anton · January 2015

To add some feed back for you, I do use both top and bottom vents, and original DFMT to regulate temps, I do use memorized standardized opening adjustments that typically bring me to next to exact temps each time, it was a long time learning curve also. I use a medium egg, and after a few months, got a HI-QUE grate, due to airflow issues. Have been happy, and consistent since. Easy to get to my desired temp now.

JNJGoeders · January 2015

This is a very good direction. I am also interested in the variances in temperature, humidity, intake and exhaust to maintain good temp control. I have had some big differences in "should be" settings and temp results... Please keep the experience and advice coming!

bigalsworth · January 2015

stemc33 said:

I often read about airflow is airflow in reference to temp control. Is this really true? What is optimum? Any fire science guys on the forum?

Sometimes my egg rocks along with tiny openings in the vents and sometimes it requires big openings. I'm not one to light my fire with the exact same OCD process that some of you do with every lighting, so I often get different results. What I do know is that I have left my bottom vent about half open a few times and the fire snuffed out by just using the ceramic cap. I realize that it probably took longer than if I closed it, but it proves airflow is not airflow. Intake and exhaust must occur. I know my coal stove always acts differently depending on outside temp and barometric pressure. If it's above 50° outside, I need to run it hot to keep enough draft going up the chimney to keep the house from filling with smoke. Just seems like so many variables when it comes to fire and am hoping one of you Eggheads is an arsonist or a Fire Marshall and can explain the science of fire.

Also, are EggHeads telling the truth about certain vent settings always produce the same results? I've gotten much better since switching to OO, but I still have an occasional fire issue.

Airflow is airflow, intake and exhaust is airflow, but there are many factors that come into play that effect airflow and the size and layering of your lump is a big one. Have you paid much attention to your lump, do you layer it with big, med, then small on the top? Probably most of the people who get consistent results with vents probably do bit of lump organization. When you stuffed out your fire with the bottom vent half open maybe you had a lot of the bottom of the bag snickle fritz blocking air flow.

The amount of ash in the bottom can have an effect, the wind can have an effect such as Honda has mentioned. Your natural draft, which is difference in "air" density from the bottom vent to the top vent makes a difference, but ultimately with 3' difference on the egg I don't know how much effect it has. Draft and barometric pressure will play a much larger role in your stove, that is why your chimney goes so high its to get a higher difference in density to get a better natural draft, if you want less problems with smoke in your house make your vent taller and put in a more precise draft control louvers.

Basically everything has to do with airflow

johnkitchens · January 2015

hondabbq said:

In one of my earliest post I mentioned this phenomena. The vent settings depending on season, temp, humidity, IN MY EXPERIENCE have an effect.
Of course wind speed has a major effect for me, as I am not sheltered from the wind like some. It can be calm or windy when I start the cook and will need to be changed sometimes if the wind dies or comes up.
Again IN MY EXPERIENCE, someone's vent settings in Texas will be different than mine up in Central Canada. I remember a post that someone never has their DFMT on and only adjust with his loser vent. I cant get below 350 that way.
In either case I am a firm believer that weather and climate have an impact day to day on the settings of the egg.

I totally agree with this. This has been my experience since day one. Some days my lump is a lot harder to light than others as well.

@anton I also got the Hi-Que grate, and it has sped things up a lot for me. I won't be going back.

hondabbq · January 2015

@bigalsworth

I have oriented my lump as you have described, and I do a clean out each and everytime I start a low and slow. I had a cook go out on me 1 time and I related it to improper airflow, so now I reset my egg for long cooks. I find this has more of an effect when the temps need to be in the lower specifics of the egg. When I am doing a 350+ cook I don't reload it.

I don't believe there is 1 generic setting for a pork butt for 275 degrees that matches up for everyone that owns an egg.

BigGreenGator · January 2015

Bottom line always clean your ashhole for good air flow

bigalsworth · January 2015

@hondabbq I agree with your above post that settings in texas will be different than settings in canada, or anywhere else. I just never included a response to every persons response here, I was just trying to explain that all the things discussed effect airflow and managing his lump may help him with a more consistent vent result not give him the exact same vent results as others.

If you live on a hill or in a valley, or flat land that is way higher above sea level than others, this all effects draft.

stemc33 · January 2015

@bigalsworth‌, I knew we had somebody on the forum that had a little arson knowledge. I don't do the lump organization thing. Just dump and light. If I get a bunch of tiny pieces, I toss em into the ash can. The EggHeads that talk about 1/8" opening baffle me. I've only had a few times when the vents were even close to that and that's after the temp has been at 500-600° and I closed them down to bring the temp down and then it'll rock steady as long as I don't mess with it. Most of the time to get 350°ish, the bottom is about an 1” and the DFMT is with petals wide open. With that said, I've reached and maintained 350° wide open bottom and petals wide open. On my long cooks, I hollow out the center and dump lit lump in the well.

The one thing I find consistent though is that when the Egg hits about 450° with the bottom and the top vents wide open it goes nuclear in the blink of an eye.

tgkleman · January 2015

It also depends on how much lump is burning when you decide to change the vent. I'll start my fire with vent wide open, and after the fire gets going, I'll adjust my vent to what I think should be right for, say 350. If the fire is large by the time I adjust the vent, I'll make the opening much smaller. If the fire is not so large, I'll adjust the vent to say half way. So it is about air flow, humidity, etc. but also about the quantity of charcoal lit... IMHO.

Jeepster47 · January 2015

Ambient air temps do have an affect on settings. A 100 degree raise in temp will result in approximately a 20% increase in air volume. A 100 degree difference in ambiant air temps from summer to winter is not uncommon in may parts of the country. Even if you argue that the inlet setting is the same, the outlet has to be open an additional 20% in the winter.

I think @anton is the idea candidate for being able to dial in temps automatically. First he has one egg and he cooks on it a lot ... thus, it's his friend. The weather conditions in his area don't range too far afield. Many of the rest of us live in areas where the humidity and temps can vary quite a bit ... as do our vent settings. He probably can't understand what the fuss is all about.

The end of the dome thermometer on my large is only 5.5 inches above the felt line. If temps in an egg were as even as we imagine them to be, then the dome temp and the raised grill would be very close ... or at least maintain a constant differential. And, they do tend to approach each other after the egg has been percolating for an hour or so. But, that condition doesn't always exist.

Case in point ... my last cook was with the DigiQ and a plate setter. For 4.5 hours the grill and the dome temps were tracking each other closely. Then the dome temp started climbing, but the DigiQ and a Maverick pit probe both said the grill was staying at 250 degrees. What I noticed was that the fire had burned towards the front of the egg. One leg of the plate setter was towards the rear, thus a gap was directly under the dome thermometer and it was now catching the majority of the hot gases. Had I been monitoring only the dome temp, then I'd of starting choking down the egg and the ribs would not have been done on time. At the end of six hours, the dome temp had climbed to 350 degrees and the grill temp was still at 250 degrees.

Our assumption is that the air inside the egg is steady and even, but I'm beginning to believe that it really is very turbulent with a wide temperature gradient. We don't see the fluctuations because the dome thermometer is slow to react, and thus, in a crude way, does a temperature averaging. For direct cooking, the dome temp is probably a good indicator of what's happening inside the egg ... and vent settings are probably more repeatable. But, throw in a flow deflector or two (plate setter, double racks, etc) and the dome temp might be a little more suspect ... and consequently our vent settings will vary more from cook to cook.

My experience, so far, is that a vent setting yesterday will not produce the exact same results tomorrow ... maybe close enough for a good cook, but still not the same. That's where expectations probably come in to play. When the recipe calls for 350 degrees, a longtime egger is happy with +/- 50 degrees and says s/he got it with the same vent setting as last week. A newbie is trying for +/- 5 degrees and can't understand why the vent settings vary from week to week.

Hmmm, maybe we should throw the thermometers away and simply paint three colors on the vents for Smoke, BBQ and Grill. Or, maybe I've got to find my meds.

hondabbq · January 2015

@bigalsworth

My post wasn't on the offensive. I was just stating that having done your suggestions I still had similar results with vent settings . No harm no foul.

gdenby · January 2015

There isn't a specific "dial in" setting, but try a search on "grandpas grub vent setting" His pictures don't match what i usually have, but I would certainly call them close.

The reason I have a problem with the notion that ambient temperature and Rh has much of a bearing is that the differences between cold dry air and hot humid air is really quite small. Assuming I did the math correctly, I looked at the weight of water in air at different temps and Rh as listed in the engineering toolbox. Did some conversions, did a rough calculation on the interior volume of a large Egg, and found that heavily saturated warm air has around 7 grams of water in it.

I'm not familiar enough with the units that describe how much energy is needed to convert that vapor to steam, or how much lump would be needed to generate that heat. In part, the problem is due to lump having different amounts of carbon depending on the type of wood used and the way the lump was made.

Considering that a drip pan will catch more fluid than that, and boil off the water w/o a vent change inclines me to think humidity doesn't have much of a difference compared to rate of air flow.

This is not to say the moisture or lack thereof in the Egg ceramics don't have an effect. If there is a lot of water soaked into the ceramic, it will take quite awhile to bake out unless the vents are open wide. But I have done some experiments based on a comment that former member stike made about just setting the vents as desired from the start, instead of shutting them down as the desired temp neared. If I use my usual setting for a dome of 250ish, it takes between 1 & 1.5 hours to get to "good smoke" and 250.

Little Steven · January 2015

I dump lump. Don't remove ash often. Probably have a pantload of ash behind the fireboxes...wouldn't know. Live where temp ranges from-30 to +95 yet my vent settings for 250 never change. Just saying.

Jeepster47 · January 2015

@gdenby ... once the egg stabilizes, I don't think the moisture that's contained in the air inside the egg affects the required airflow ... that stays reasonably constant. The moisture that comes in from the outside as a part of the combustion airflow is what would affect the vent setting. That moisture gets warmed up to internal temp before it exits the egg in the exhaust stream ... and that takes more lump burning, and thus, more airflow. I don't know how to measure/calculate airflow, so can't comment on how much it affects the vent openings. Maybe an HVAC guy could add some insight.

Grampas grub vent settings were/are a fantastic reference. They really helped me understand how small the bottom vent opening was for a 350 degree temp ... probably prevented me from carbonizing a few chickens.

Jeepster47 · January 2015

Little Steven said:

I dump lump. Don't remove ash often. Probably have a pantload of ash behind the fireboxes...wouldn't know. Live where temp ranges from-30 to +95 yet my vent settings for 250 never change. Just saying.

Will you trade eggs with me? Mine is not as well mannered. It'd be nice to have someone train it to behave and stop screwing with me.

Oh wait a minute ... nope ... then I'd have learn to talk to it in Canadian: "Hey egg, cook good, eh!"

Carolina Q · January 2015

Wow. Lotsa words written here. Didn't read most of them. I'm with LS. except way more of my cooks are at 400 than 250. Always the same settings though. Air is air. Just stir old lump, dump more in if needed and use a wiggle rod.

gerhardk · January 2015

In my opinion the people that have airflow issues are the micro managers of the temperature. I agree with Little Steven the ambient temperature seems to have little effect on the vent openings required.

Gerhard

johnkitchens · January 2015

gerhardk said:

In my opinion the people that have airflow issues are the micro managers of the temperature.

Micro manage my temp??? Just because I like to cook at 387.1 not 387.2 doesn't mean I am a micro manager!

Little Steven · January 2015

Jeepster47 said:

@gdenby ... once the egg stabilizes, I don't think the moisture that's contained in the air inside the egg affects the required airflow ... that stays reasonably constant. The moisture that comes in from the outside as a part of the combustion airflow is what would affect the vent setting. That moisture gets warmed up to internal temp before it exits the egg in the exhaust stream ... and that takes more lump burning, and thus, more airflow. I don't know how to measure/calculate airflow, so can't comment on how much it affects the vent openings. Maybe an HVAC guy could add some insight.

Grampas grub vent settings were/are a fantastic reference. They really helped me understand how small the bottom vent opening was for a 350 degree temp ... probably prevented me from carbonizing a few chickens.

Kent is from the high plains of Idaho or Wyoming or some such. Thin air out there apparently. His settings are way different than mine.

Little Steven · January 2015

Jeepster47 said:

Little Steven said:

I dump lump. Don't remove ash often. Probably have a pantload of ash behind the fireboxes...wouldn't know. Live where temp ranges from-30 to +95 yet my vent settings for 250 never change. Just saying.

Will you trade eggs with me? Mine is not as well mannered. It'd be nice to have someone train it to behave and stop screwing with me.

Oh wait a minute ... nope ... then I'd have learn to talk to it in Canadian: "Hey egg, cook good, eh!"

I don't understand all this trouble. When I refer to the egg I mean the large. The mini, small, medium and XL are different.

And you would have to use superfluous u's in places where they shouldn't be.

Little Steven · January 2015

gerhardk said:

In my opinion the people that have airflow issues are the micro managers of the temperature. I agree with Little Steven the ambient temperature seems to have little effect on the vent openings required.

Gerhard

Or maybe they don't wait long enough? Maybe expect the egg to cool quickly if they overshoot. Dunno.

Carolina Q · January 2015

Kent is in Utah. But yeah, altitude.

Wonder how he's doing. Haven't heard from him in ages.

caliking · January 2015

You're overthinking this. As stated above, fire in the egg needs air, fuel, and ignition. After that, there are lots of variables that come into play, and its not worth trying to account for all of them.

When I first started egging, the permutations of the DFMT and intake vent to maintain a given temp was driving me batty, and the damn thing would slide around and cause trouble after a few beers (clearly the DFMT's fault), so I stopped using the DFMT. Took it off and controlled temps with just the intake, like I do with my kettle grills. Then I bought the Smokeware cap and love it. But even with the cap, I still slide it all the way open and control the temp with the lower vent. Some folks do the opposite - intake open all the way, and control using the top vent (smokeware or DFMT).

It may take some practice/experimentation, but that's why God made beer, to keep you company while you figure out what works best for you

bigalsworth · January 2015

Jeepster47 said:

@gdenby ... once the egg stabilizes, I don't think the moisture that's contained in the air inside the egg affects the required airflow ... that stays reasonably constant. The moisture that comes in from the outside as a part of the combustion airflow is what would affect the vent setting. That moisture gets warmed up to internal temp before it exits the egg in the exhaust stream ... and that takes more lump burning, and thus, more airflow. I don't know how to measure/calculate airflow, so can't comment on how much it affects the vent openings. Maybe an HVAC guy could add some insight.

Air (kg per kg of fuel) = [8/3C + 8(H2 - O2/8) + S]100/23

C = Carbon per Kg of fuel
H2 = hydrogen per kg of fuel
O2 = oxygen per kg of fuel
S = sulphur per kg of fuel

Also the vaporization of water into steam decreases efficiency more than anything, the latent heat of vaporization of water is 2257KJ/Kg and the sensible heat used (taken) to help with the physical change in water to steam would be negligible.

I have the same settings most of the time until I get to the bottom of a bag. I don't throw out any of the small pieces, I just dump them on top. I have had to keep my vents open wider and longer to reach my desired temp but as the lump burns I will eventually have them shut to my normal settings. I am with @hondabbq I cannot have my vent off without it going out of control, and wind really effs it up.

I also think this has been way over thought and admittedly am helping way over think it. But I also find the discussion interesting so add to it. 20 different things may all effect the what draft is needed but each of them on their own are negligible. Maybe the sum of their parts can make a noticeable difference.

anton · January 2015

@Jeepster47, you are right, I do have the ideal temp and no humidity to speak of here in Ca. I know you guys with wind chill factors, wind, humidity, etc, all plays a part. And I can testify to your suspicions that the air is turbulent inside, remember that picture of my funky daisy wheel? I put it in the egg to clean it on a clean burn, and it made circular burn marks on it! Proof that the air is twisting and turbulent during a high heat clean burn at least. I imagine it winds around a little bit from the round shape of the egg. We need a high temp camera inside one of our eggs to see it in action now!

Airflow is airflow (Is this true?)

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