Expansion tank for heater overflow works on heaters up to 50 gallonPowder coated interior shell protects against corrosion, assures long trouble free lifeExterior powder coat paint for long life and anti-corrosion, certified to automotive ASTM standardsProper tank sizing is critical to the performance of your water heaterNSF and IAPMO approvedIf your home was built in 1985 or is newer, you should use an expansion tankThere is a check valve on your meter closing the system and creating negative thermal expansion impact