When the E-Cat is turned off, there is still a hot iron core at 600 - 1000C, depending on who you listen to. It has lead shielding. If there are adjacent cats, they will also heat up, storing additional heat. Depending on the description, this may or may not be in the bottom; it may or may not be connected to the heat exchanger.
This is not a calc but I agree with Jed. I worked some years ago in a steel mill. When water meets 600-1000C metal ka-boom. At lower temps the specific heat of vaporization of water greatly exceeds the specific heat of a metal. Frank Z
