Relationship b/t top and bottom damper

redneck6497

Hi All,

I want to understand more about the relationship between the top and bottom dampers. I was cooking pizzas last night at 600 deg. I realized I really don't know that much about the top damper. My temp went down to 550 after 2 hrs of cooking (expected due to the charcoal level). I had the top wide open. My friend said to close the the damper way down. The temperature went up by about 20 or so deg. I didn't really have time to watch it for a while, but my expectation is that initially it would go up, and then smother the fire even further. Is this the case?

Can someone tell me the relationship between the top and the bottom? I make most of my major adjustments with the bottom, but don't really ever know what to do with the top.

Capt Frank

Go to the search forum and type in "recipes, links & tips". You will get a great post by Grandpa's Grub that among many other topics, has a pictorial explanation of vent settings.
Bookmark the post, it is a terriffic resource
Welcome aboard!

Hillbilly-Hightech

Hi,

I think of it this way - the bottom damper is the air intake, and the top damper is the air exhaust.

Both work in concert w/ each other. Fire needs 3 things - fuel, oxygen, and heat / ignition.

However, it also needs to exhaust the burnt fuel & oxygen gases. The concept is exemplified by how your car engine works - gas is the fuel, which gets ignited & burned in your engine, then exhausted out your tailpipe.

If someone were to put a banana in your tailpipe, it wouldn't be long before your engine stopped running.

This is because as the fuel & oxygen chemically react, they exhaust burnt gases (not sure what all they exhaust, but I think it's CO, CO2, and I'm sure many other gases). Anyway, if you're trying to burn something but don't allow the burnt gases to escape, then eventually those burnt gases will occupy all the volume in your engine (or your Egg, in your case) and will not allow any NEW unburnt air (oxygen) to come in to feed the fire.

Then basically, your fire will get "snuffed out" because you've essentially cut off the oxygen input (again, remember - one of the 3 parameters needed for fire).

I have (accidentally) allowed my Egg to run "full force" before (meaning, bottom damper wide open, and top daisy wheel completely off) - with full air in, and full exhaust out - that puppy will get WELL above 700-800 degrees, usually in less than 20 minutes!!

That's where we, the people doing the BBQing & grilling, come in - to start controlling the input & output, so that you can control the temperature.

I think someone at sometime posted some pics of where the daisy wheel needs to be in relation to how open or closed the bottom vent needs to be for certain temps - and if they care to repost the link or the pics here, that's great.

But remember, that's JUST a guide - the elevation where you live, the type & amount of lump you have, whether or not you're re-using the lump, whether or not the lump has gotten damp, the amounts of fires you have (whether or not you lit the lump in one place, or 3 places, etc), how much wind is going on, the outside ambient temp, etc are ALL variables which can affect where the top & bottom vents should be positioned on any given attempt for a desired dome temperature.

What seems to work for me is that when I first light the Egg, I'll have the bottom vent wide-open, and the daisy-wheel completely off. Then, if needed, I'll take my old trusty fireplace bellows, and place the brass tip of the bellows just inside the bottom vent hole & use them to force more air into the bottom of the Egg. Sometimes I need to use the bellows, sometimes I don't. Sometimes I need to use them for several minutes, sometimes I need to use them only once or twice - again, this is all dependent on the variables I listed above.

Then, assuming I don't go into the house & forget to put the daisy-wheel back on & start closing the bottom vent (as has happened to me on more than 1 occasion) - I can start slowly shutting both the bottom & top vents down until I attain the desired temperature.

Some folks on the forum feel that "overshooting" the temp is a major "no-no" and that it's very difficult to get the temp back down once you've overshot. However, in my experience, sometimes it's quicker & easier for me to overshoot & come back down, than it is to try to "dial-in" the correct temp as it's coming up.

I've done it both ways before, so it doesn't really matter (in my opinion) if you approach the temp coming up from below it, or if you overshoot & bring the temp back down.

And as I said, there's some pics showing the relationship of top to bottom vents, but for me, I just play with each & tweak each. For example, if I know I need to shut the bottom vent down because it looks like I might overshoot the temp, I'll close the bottom vent a little bit - then I'll close the daisy-wheel a little bit as well (maybe just turn the dial on the daisy wheel to cover the little holes). I'll usually cover the little holes before I actually start closing off the large hole on the daisy wheel. Again, this is just my personal preference.

At any rate - hopefully you understand the relationship between the top & bottom vents a bit better, especially if you picture the bottom vent as the intake, and the top vent as the exhaust.


HTH,
Rob

Hillbilly-Hightech

ooops - didn't read Capt Frank's response where he stated that is was Grandpa's Grub who posted the pics showing the vent positions.

I looked it up, and here's that link:

http://www.eggheadforum.com/index.php?option=com_simpleboard&func=view&id=670088&catid=1

And here's the more general, and much more informative, overall link showing all the other "tips & tricks":

http://www.eggheadforum.com/index.php?option=com_simpleboard&func=view&id=770276&catid=1#

HTH,
Rob

stike

no relationship.
you can use one or the other or both

redneck6497

Thanks to everyone for the information!

Hillbilly-HIghtech,
Thanks for writing all of that info. out, and posting the links!