Aside from keeping the warm air from escaping, the doors act to keep the hearth clean just as a fireplace screen used to do in the olden days. With the doors closed, ashes and embers don't scatter about the room, keeping the carpet or rug clean and scorch-free. The doors also have built in devices that divert air towards the bottom of the fireplace. These vents make the fire burn brighter and easier to light.
Again, you will also be fascinated by another modern fireplace which has a toughened surround glass that projects a "disappearing" effect. It has sleek and cool lines. Its steel bench hangs between the glass surround creating the illusion of dancing flames off the reflective glass screens. One more type is a cylindrical shaped "teal light" outdoor fireplace. It is a free standing portable type with a round stainless steel base encasing an ethanol burner. It can be operated by using the lid which puts out the flames when it is in the proper position. The uniqueness of this version is the elevated flame with its brilliant light above the steel base brought about by its raised up tempered glass surround.