Z-VENT Commercial reduces total installed vent system cost. Patented factory-fitted fail-safe sealing gaskets install in half the time of field-sealed systems. The precision-engineered close tolerance construction ensures an air and water tight fit. Leakage tested to 2½ times UL pressure rating of 8-inch W.C. Z-VENT Commercial Special Gas Vent System is tested and listed by Underwriters Laboratories to UL 1738 venting systems for gas-burning appliances, Category II, III and IV.