Modern Fireplaces Gas - A fireplace glass door is installed on a hearth to keep the room warm when the flames die down. Whether a wood burning fireplace or a gas burning fireplace, heat radiated into the room escapes. While the fireplace is burning brightly, because of the heat in the flames that radiates to the room one does not notice this.
When the fire starts to die down, the fireside becomes cool quickly as the heat escapes through the fireplace opening. To stop this from happening, a fireplace glass doors blocks the opening, maintaining the heated air from leaving the area.
Besides keeping the hot air the doorways act to keep the hearth clean just as a fireplace screen I did so in the olden days. With the doors closed, ashes and embers don't scatter about the space, keeping the carpet or rug scorch and clear -free. The doors also have built in products that divert air towards the base of the fireplace.