Country Fireplace Inserts - A fireplace glass door is installed on a hearth to keep the area warm when the flames die down. Whether a wood burning fireplace or a gas burning fireplace, heat radiated to the area escapes. One doesn't notice this while the fireplace is burning brightly, mainly because of the heat in the flames that radiates into the room.
When the fire starts to die down, the hearth becomes chilly rapidly as the heat escapes through the fireplace opening. A fireplace glass doors blocks the opening, maintaining the hot air from leaving the room, to stop this from happening.
Besides keeping the heated air the doorways act to keep the hearth clean as a fireplace display used to do in the olden days. With the doors closed, embers and ashes do not scatter about the room, keeping the carpet or rug scorch and clean -free. The doors also have built in gadgets that divert air to the bottom of the hearth.