On Demand System 1738® is the first engineered PVC Flue Gas Venting (FGV) System certified to UL 1738. The safety concern today is in the use of plumbing Solid Wall Schedule 40 or Cell Core DWV pipe and fittings in FGV applications. These products were never intended to be used in FGV applications, but they have been chosen because they are often the least expensive materials available. Simply put, plumbing DWV products are NOT designed to meet the life safety standards of FGV applications.