Newer prefabricated fireplaces are more energy efficient than traditional masonry ones.
Must use a venting system. In a conventional, open-face fireplace, the chimney serves as the vent. The drawback is that it pulls warm air up the chimney and out of the house.
A prefabricated fireplace has an enclosed firebox made of a material that will hold some of the heat from the flue gases so more heat is radiated back into the room.
Fireplace systems will incorporate a damper in the flue, which can be closed when the fire is extinguished. Otherwise, the warm air will continue to flow out of the house through the draft that is created.