Volatile constituents can sometimes condense in the early preheat or early cooling in certain tunnel kilns. At times, the condensates fall on the product and cause dirt defects. Sometimes the condensates are so chemically reactive that it damages the kiln lining by fluxing the refractories in both the preheat and cooling zones. In either case, undesirable precipitation of volatiles can cause serious product loss or even kiln damage.

Tunnel kilns account for the bulk of worldwide ceramic firing. For many products, a tunnel kiln offers the potential for better temperature uniformity and product quality—with an energy consumption that is typically half that of periodic firing systems.