The Eastman? 4.5-Gallon Thermal Expansion Tank has a secure connection to water heaters that prevents dangerous build-ups of pressure. This water heater expansion tank stops hot water from backflowing into the cold water line and it also prevents hot water from escaping through the pressure relief valve and onto the floor. Constant fluctuations in water pressure can be dangerous and they can damage the water heater properly installing a thermal expansion tank can solve all these issues. This product comes with a 6-year warranty and is factory pre-charged at 40 psi. Complies with NSF-61 and Lead Free law. UPC approved.