A combination fireplace furnace and cookstove is adapted for insertion as a unit into the front opening of an existing fireplace. Such apparatus includes a firebox portion adapted for positioning within a fireplace and a cookstove portion provided with a cooktop, designed to protrude into the room when the apparatus is installed in a fireplace. A sheet metal jacket around the firebox portion encloses an airspace communicating with air intakes at the front of the unit. Heat exchange tubes communicating with the airspace at the back of the firebox pass through the firebox and cookstove portions to discharge openings at the front of the unit so that air warmed in the airspace is further heated in such tubes before discharge into the room. A baffle within the firebox directs products of combustion forwardly into the cookstove portion to heat the cooktop and upper heat exchange tubes before passing up the chimney. The baffle includes a damper movable between an open position to allow combustion products to rise directly up the chimney and a closed position to heat the cooktop. The cookstove portion has a front opening closed by one of a group of interchangeable doors.