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Do Kilns Fire Cooler on the Bottom?


Do Kilns Fire Cooler on the Bottom?

Recent Q&As: A kiln’s maximum firing rate; shelf placement in the Fusion-10 glass kiln

Tornadoes ---------------

You may remember from eighth grade science class that heat rises. This is called convection. Many years ago it was a common belief that large kilns fired cooler in the bottom because heat rises.

Kilns tend to fire cooler on the bottom, but not because heat rises. Movement of heat through convection ends at around 1100 degrees F. At 1700 F, a cubic foot of air has only about one-tenth the number of molecules as at room temperature. This is why there is little airflow in an electric kiln at high temperatures.

The bottom and top tends to stay cooler because the brick bottom and lid are large thermal masses that absorb energy. Paragon compensates for this by making the bottom and top elements fire hotter than the center elements.

You can improve heat distribution inside the kiln by loading less ware in a cool section and more ware in a hot section. Slowing the firing also helps.


Q. I got an error code FTH (Failed to Heat). When the temperature climbs to 1200F-1300F my kiln fires at a maximum rate of 440 F; at 1400F-1500F the maximum rate is 360, and at 1500F the maximum rate is 300. I don't understand why my kiln fires at a progressively slower rate as the temperature climbs.

A. Kilns slow down as they go up in temperature. Their fastest firing rates are in the lower temperature range.

The maximum firing rate of a kiln depends on the type of insulation, element design, amount of wear on the elements, the size of the kiln, the voltage available at the wall receptacle, and other factors. Ceramic fiber kilns fire faster than equivalent firebrick kilns. Our fastest kiln is the QuikFire 6, which can reach 1000 degrees F in five minutes. The larger kilns fire much more slowly.

The FTH (Failed to Heat) error message is to let you know that your kiln could not keep up with the rate you programmed. The kiln will continue the firing, though. It is not necessary to turn off the kiln when FTH appears.

It is good that you have determined your kiln's fastest firing rates for each temperature range. You should program rates that are no faster than your kiln will fire. Otherwise you will get the FTH error message again.

Q. What is the best height for the shelf in the Paragon Fusion-10 glass kiln? It has side elements in addition to the large top element.

A. We recommend 1/2" tall posts under the shelf in the Fusion-10. This height aligns the shelf with the side element for even heating. But you should feel free to experiment with shelf height too.


This week we had another tornado. It touched down between Dallas and Ft. Worth. But the tornado stayed away from Mesquite.

I've seen funnel clouds, but I've never seen one touch down. They look like a "V" when they begin taking shape, extending downward from a dark cloud mass.

After I had been working here a couple of years, a tornado came within four miles of the Paragon factory. Tree branches were strewn across the roads, and daylight turned almost as dark as night. The power went out. People in the office huddled together in a bathroom, lit by a candle. One woman prayed out loud, her voice barely audible over the roaring wind and the creaking of the steel building. A moment later the wind died, and all was calm again.

Thank you,

With best wishes,

Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 /

PRIVACY NOTICE: Under no circumstance do we share or sell your email address.

Copyright 2007, by Paragon Industries, L.P.

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