Abstract: A prefabricated fireplace structure is convertible to function as an open fireplace or an enclosed, solid fuel burning stove. An outer fireproof cabinet for installation in existing building framing or new construction, receives a selected compatible firebox in the form of a log-burning fireplace or a substantially enclosed wood/coal-burning stove. The selected firebox includes a damper and an exhaust outlet therein, which exhaust outlet is connected to a flue pipe in the outer cabinet. A unique connecting device secures the selected firebox in the cabinet and further includes a means for sealing the connection of the exhaust outlet to the flue pipe inlet.