Fireplace doors are meant to be closed when the fireplace is in use as well as when it is cold. The reason for this is that the doors are meant to be a safety feature. The fireplace doors will keep sparks and embers from flying out of the fireplace and onto any person or object that is close enough to the fire. Without fireplace doors, there is a strong possibility of an ember falling onto a carpet in front of the fireplace and starting a house fire. Because they need to be closed when a hot fire is burning, some materials are better than others are for fireplace doors. Fireplace glass doors are usually the best choice. First, the glass can withstand very high heat before you have to be concerned about anything melting or cracking, especially ceramic glass. Second, ceramic glass will let heat radiate through the doors so that you still enjoy the heating effects of the fire and the heat is not just trapped inside the firebox. Finally, glass fireplace doors are beautiful. You can have beveled glass or glass etching on the fireplace doors to enhance the aesthetic of this decorative element.