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Kiln Pointers

The Downdraft Vent Intake Holes

The Orton Vent Master.


The Downdraft Vent Intake Holes

A Pointer from Steve Mills: Improving element performance

Recent Q&A: Kiln fires glass to wrong temperature


The downdraft vent system is used on larger kilns (not the small tabletop models). It pulls a small amount of air from the kiln, dilutes it with room air, and vents the air to the outside of the building. There are several brands of vents available. An example is the Orton Vent Master.

Most top-loading kilns with the downdraft vent have 1/4” air intake holes drilled in the lid. Try not to place ware directly under these vent intake holes. The room temperature air coming in through the holes can cause small areas of glaze imperfection such as crazing, cloudiness, or even cracking of the ware. The intake holes should be drilled near the outer edges of the lid so that they won't interfere with ware placed toward the central area of the top shelf.

One way to protect ware from cool air under an intake hole is to position a small scrap of shelf over the ware. Support the shelf with a post. Do not block the intake hole with the shelf.

Another method is to temporarily plug the intake hole with ceramic fiber and re-route the air into the kiln through a drilled peephole plug. The hole in the plug should be no wider than 1/4”. Keep ware at least 3 inches from the drilled peephole plug.

Sometimes a loose peephole plug allows the vent to pull enough air into the kiln to cause glaze blemishes. In this case, keep ware 3 inches away from the peephole. Or wrap the peephole plug with a little ceramic fiber to make it fit snugly. (Ceramic fiber is available from ceramic suppliers.)


Steve Mills of Bath in South West England wrote, “This actually goes back a long way to the early '80s when my wife and I were running a ceramic supply business alongside my production pottery. I fired a four cubic foot electric kiln virtually every day.

“When one day I suddenly had a very slow firing, I asked around and was advised to vacuum the kiln out. The result was an immediate cure, and I clocked that for future reference. Since then I vacuum every four firings, advising our customers to do the same. The advice has also helped others with slow firing kilns.

“Every time a kiln is fired, it increases fractionally in size and shrinks again as it cools. With any brick, but in particular with soft brick, this movement creates dust by abrasion--admittedly very small amounts--but it adds up and can affect the operation of the elements.

“As we all know, a bisque explosion creates loads of dust very suddenly. This is more insidious yet can go unnoticed.”


Q. My digital kiln fully fused glass at a programmed temperature that should have only lightly fused it. How do you correct a kiln that is firing around 50 degrees too hot?

A. If the kiln overfires by the same amount every time, lower the programmed temperature by 50 degrees or whatever temperature is necessary to compensate for the overfire.

If the kiln is firing inconsistently, check the thermocouple wires. They should be securely connected at the controller and the thermocouple. Make sure the wires are connected to the correct color-coded terminals. The thermocouple should extend into the kiln by around 3/4". If all of that checks out okay, then replace the thermocouple.


My niece Alina just had a baby girl in Hawaii. I remember as if it were last week when Alina was a five-year-old taking ballet lessons.

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 2008, by Paragon Industries, L.P.

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