Adjusting Kiln Draft

Noticed some problems in the last firings regarding evenness of temp. I think I’ve always had them, but just recently started to take notice of them as something that needed fixing. I’d noticed that temp from top to bottom was more than a cone in difference, with the top back even hotter. I tried raising the bottom shelves a bit to get more draft moving through. This resulted in a couple of firings that were mostly throw aways. Temp was all over the place, not just top and bottom, but front to back as well. (I was getting pretty fed up at this point)

After asking around (my mentor as well as some very nice folks at the Claycraft email list), the general concensus was that I needed to reduce draft in the rear so the heat would come up front. The idea being that the kiln gets hotter where the flame flows. This ran contrary to how I’d understood this issue in the past (I was thinking in terms of heat alone, not in terms of heat as a by product of the flame, perhaps because I’ve never fired a wood kiln. In a gas kiln it is nigh impossible to view the flame movement in the kiln) but since my way of thinking wasn’t resulting in solutions to the problem, trying something new was a no brainer, especially considering the experience of the advisers in question.

I reconfigured the shelf setting configuration so that it was now divided front/back, rather than left/right. (The manufacturer set the shelves up in left/right pairs when they installed the kiln and I never thought to change.) In addition, I lowered the back pair about a centimeter lower than the front, and layed some old posts sideways between the shelf and the car at the back and sides.

I loaded the kiln leaving less space between levels on the rear setting, and packed things in a bit tighter. In front, I packed more openly and left more headroom above the ware on each level. The results were great. For the first time ever, I fired with less than one cone difference from top to bottom, and the back was actually a bit cooler than the front. A little tweaking should bring it up to match the front.

With the exception of some experiments in the top rear, just about everything is a keeper. This was my best firing ever in terms of results of firing process.

2 thoughts on “Adjusting Kiln Draft”

  1. hey,
    i came over to visit after reading a post on claycraft. nice stuff. how big is yoour kiln? do you fire with gas or wood?

  2. Hi Trisha,

    This kiln is gas, and about 10 cubic feet of stacking space, so I have the chance to fire frequently. I’m working on plans for a wood kiln that I hope to have a kiln building workshop for in 2010. I want to do a combined workshop: Kiln building/pottery techniques/kiln firing.

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