The present invention provides a water vaporizer including a first flow path connected to a water inlet, a second flow path for receiving superheated water vapor from the first flow path and being connected to a vapor outlet to exhaust the superheated water vapor, and a third flow path extending between an exhaust inlet and an exhaust outlet and being oriented to transfer heat from an exhaust flow to the superheated water vapor. The water vaporizer can also include a first convoluted fin positioned along the second flow path, and a second convoluted fin positioned along the second flow path adjacent to and separated from the first fin to define a gap extending between the first and second fins along a length of the first fin in a direction substantially parallel to the exhaust flow along the third flow path.