Abstract: A regenerative air preheater with cylindrical regenerator chamber and sealing frames at its axial ends with adjustable automatic thermal compensating devices for uniformly maintaining a constant sealing gap by adjustable means under different heat distortions of the regenerator chamber. The sealing frames are movable on spring-loaded pins and the axial travel of said frames is automatically equalized to the axial distortions of the regenerative chamber by said automatic thermal compensating devices in such a way, that they may follow the axial distortion movement of the regenerator chamber in a constant distance of a predetermined sealing gap, which had been adjusted, said compensating devices are controlled by their temperature-responsiveness, preferably in accordance with the mean temperature difference across the mass. As shown, they are made up by partially compensating thermal expansive devices, tied to a lever linkage with adjustable means.