The down-draft vent system pulls a small amount of air from the kiln, dilutes it with room air, and vents the air to the outside. There are several brands available.
The down-draft vent is used mostly on ceramic studio kilns. But it is also useful in glass kilns if you use fiber shelf paper or any materials that produce strong fumes.
Some vent systems do not use air intake vent holes. For instance, the Paragon Dragon does not need vent holes. But most top-loading kilns with the down-draft 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. The vent intake holes should be drilled toward the outer edges of the lid so that they won't interfere with ware placed toward the central area of the top shelf.
You can place ware near the vent exit holes, however. In most top-loading kilns, the exit holes are drilled in the kiln bottom. The movement of air will not interfere with ware because the exit air is hot.
With the vent, you can mix glazed ware and greenware on the same shelf in the kiln. Because the atmosphere is oxygenated and replenished, glazes are not as affected by surrounding ware.
Leave the vent on throughout the kiln firing and cooling cycle. Turn the vent off when the kiln is cool enough to unload barehanded. The vent will help remove moisture during “candling” at the beginning of the firing. The moisture inside the duct and motor will dry out as the kiln heats.
I hope you're having a great summer.
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 firstname.lastname@example.org / www.paragonweb.com