If you are referring to Daguerreotypes, the process required development of the silver coated copper plate in mercury fumes. The plate would be suspended over a crucible of warmed mercury and the latent image was rendered visible. The only reason to heat a paper print is to make it, as an object, perform an aesthetic function, ie be arty, but there is no other process that involves heat than the daguerreotype that I can recall.
The first practical photographic process was the daguerreotype process. No film but a silver plated copper plate. This plate was hovered in a chimney of a lantern, just above the flame. A teaspoon filled with iodine was heated by the flame. Iodine vapors drifted up the chimney, the iodine interacted with the silver forming the light sensitive compound silver iodide. This plate was then inserted into the camera and exposed. After the exposed plate was developed and fixed and washed, a finished beautiful photograph resulted. Even with all our technology we can