Made in the USA from AL29-4C steel and meets UL1738 standard. Z-Flex vent pipe is specifically designed for Category III (standard efficiency/non-condensing, power vented) and Category IV (high-efficiency/condensing, power vented) appliances, including ALL tankless water heaters and wall-hung boilers, as well as storage type water heaters and floor-standing cast iron boilers. Note: we also carry NovaVent pipe by Z-Flex which meets the same high standards as Z-Vent pipe, but is more affordably priced.