ZEP-1 Zilmet USA Stainless Steel Expansion Tank Introducing the NEW Zilmet USA ZEP-1 Stainless Steel Expansion Tank and Shock Arrester for Tankless and POU Water heaters with 2 gallons or less of total water volume.Most tankless water heater manufacturers require a thermal expansion tank with their water heaters when a backflow preventer is required. The compact ZEP-1 is the perfect solution for providing thermal expansion protection in tight places. Stainless steel construction and NSF 61 certified. Tank has a 50 PSI factory prechargeAir charge can be adjusted, and is serviceableEntire tank is constructed of 304 stainless steel1/2 in NPTM 304 stainless steel connectionUV resistant and approved for outdoor installationButyl membrane diaphragmNSF61 Certified