baffle shelf on gas kiln exhaust port

[docweathers]

I understand that some people place an extra shelf about 5 cm below the exhaust port on updraft kiln such as my Olympic 2827G. Can someone explain to me if, how and why this works?

 

Why would this be any different than putting a brick partially over the exhaust port?

 

Thanks Larry

[Brian Reed]

I have a updraft gas and I do put a shelt about 2 inches below the lid. The directions said to do it becuase of the way the gas heat moves, not sure exactly why, but makes sense. Perhaps it allows for a certain amount of downdraft of the heat prior to going out.

 

 

 

Sorry I cannot explain why, but thought I would let you know that I do it.

 

 

 

I have a Crucible 10CF Updraft with 4 burners that I fire with two 100lbs propane tanks plumbed together.

I am able to fire to ^10/11 in reduction. Getting reduciton in this little updraft was a labor or love and patience, but I am getting decent reduction everytime now.

[Mark C.]

The reason is to slow the exhaust heat down to promote even heating. My small 12 cubic foot updraft always has a cold top(not as hot as bottom) and this gets the top a tad hotter as the gasses slow down before the exit damper lets them out.

Also On certain glaze fires it reduces better.

Hope this helps.

Mark

[docweathers]

I don't doubt that this procedure works. I just have a compulsion to know why things work. Essentially my question is, How is the shelf different from restricting the exhaust port slightly with a brick?

[neilestrick]

Think of it as creating a smaller heat chamber within the kiln. It helps to hold heat in, but doesn't really affect the draw of the exhaust. Gas kiln fire by moving heat through the kiln, not trapping it in. Blocking the exhaust/damper affects the draw and prevents the air from being able to move through the kiln efficiently. The shelf near the top acts as a heat baffle, but not a draft baffle.