PPP: Venting Electric Kilns

If your kiln is in a basement, garage, studio or classroom, exploring kiln ventilation is a good idea.

A hood-type vent.

After seeing the title of this article, you might be asking why anyone would need to vent an electrically fired kiln, since there are no products of combustion like those found with gas-fired kilns. It used to be a common practice to prop open the lid of an electrically fired kiln at the start of the firing cycle, and there’s a good chance that you’ve noticed the unpleasant odors arising from those kilns during the first part of the firing process.

If your kiln is located outside in a lean-to with ample natural ventilation, you probably don’t need to be concerned. If your kiln is in a basement, garage, studio or classroom, though, exploring kiln ventilation is a good idea.

Vent mounted on the floor. (Courtesy of Jim Bowling, assistant professor, Otterbein College, Department of Art, Westerville, Ohio.)

Understand the Oxidation Process

Let’s consider the sources of the odors that are emitted in your kiln during the firing process. Clays and glazes contain various amounts of organic material. During firing, these carbonaceous materials oxidize, consuming the free oxygen in the kiln. Depending on the temperature, firing rate, and amount of available oxygen in the kiln, carbon dioxide and/or carbon monoxide will form.

If you combine high-organic-content clay with a heavy load in the kiln and a rapid firing rate, you can create a situation where there is insufficient oxygen available to oxidize all the carbonaceous material in the body. As a result, as the clay body begins to seal, the trapped gases can cause black coring and/or bloating to occur.

The old-school approach to preventing insufficient oxidation is to keep the lid of the kiln open while it is warming. Once the kiln reaches a point where odors are no longer emanating from it, the lid is closed. When used within reason, this practice works fairly well, as long as the room is large enough to dissipate the odor, or you simply exit the area and come back later.

The downside to this approach is that, after time, any windows in the area become frosted, any exposed metal prematurely corrodes, and the room is unbearable to work in when the kiln is firing. You also need to remember to shut the lid!

Vent mounted on wall and used to vent two kilns. (Courtesy of Halee Rogers, art teacher, DaVinci Academy of Science & The Arts, Ogden, Utah.)

Evaluate Better Options

Thankfully, through a little ingenuity and the desire to fire more efficiently, better ways to vent kilns have been devised. Two schools of thought exist regarding how to best exhaust electric kilns. The macro approach requires whole-room ventilation: a large hood is placed over the kiln to catch the odors as they escape, and a fan is mounted within the duct to collect the odors as they rise with the heat and blow them outside.

This method can require an expensive make-up air system due to the high volume of air that must be re-circulated to remove the kiln exhausts. Greater expense can be encountered from higher heating and cooling costs due to the amount of makeup air needed, as well as the initial cost to install the required ductwork and exhaust hoods. This approach also limits the location of the kiln to one specific area or room (where the hood is located) and does not eliminate the need to prop the lid open to allow for the influx of air.

On the other hand, the micro approach continuously removes a small amount of air from the kiln during firing. A low-volume fan attached to the bottom of the kiln creates suction on the inside of the kiln. Fresh air is drawn into the top of the kiln while the fan draws the byproducts into an exhaust duct. To keep the system from getting too hot, the kiln exhaust is mingled with the cooler room air and blown outside. The fumes are never allowed to enter the room.

This approach ensures that the atmosphere inside the kiln remains oxidizing, which promotes the complete oxidation of any organic compounds found in raw materials, binders and decorating mediums like waxes. Additional benefits include longer element life; improved temperature uniformity; better glaze color development and gloss; location flexibility; the ability to remain in the work area during firing; a much quieter work area; and the freedom to fire the kiln without having to prop open the lid.

The kiln exhaust is mingled with the cooler room air and blown outside. (Courtesy of Jim Bowling.)

Effective Venting

Choosing to install a vent that operates under the micro approach presents distinct advantages. In today’s economy, getting the best value for your purchase is more important than ever. Given the many benefits associated with utilizing the micro approach to venting kilns, your best value can be realized by installing a vent that operates under that principle.

For additional information regarding kiln ventilation, contact the Edward Orton Jr. Ceramic Foundation, 6991 Old 3C Highway, Westerville, OH 43082; (614) 895-2663; fax (614) 895-5610; e-mail infor@ortonceramic.com; or visit www.ortonceramic.com.


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