The Eastman thermal expansion tank is designed to prevent dangerous build-ups of pressure in your water heater tank. Stops hot water from backflowing into the cold water line while preventing hot water from escaping through the pressure relief valve and onto the floor, addressing the constant fluctuations in water pressure that can be dangerous and potentially damage your water heater tank permanently. Recommended for homes with a closed-loop water supply system, this product comes with a 6-year limited warranty and is factory pre-charged at 40 psi. It complies with NSF-61 and Lead-Free law.