Direct-Vent fireplaces are now the most popular type of fireplace sold nationally. These units have a sealed glass front face, and the double-wall chimney provides combustion air for the fire as well as exhaust from the burning process.
Direct-Vent fireplaces are popular because of their high efficiency and their beautiful burn characteristics. Their design as a sealed combustion system results in a clean, efficient fireplace that does not communicate with your room air.
The chimney can be vented vertically with a short stack through the roof, or it can be elbowed 90 degrees and vented horizontally out of a vertical wall and terminated.
Because the Direct-Vent fireplaces are vented, they can burn dirtier than a vent-free fireplace and the result is burning characteristics more like a natural wood-burning fireplace in the traditional models. The long, narrow, contemporary linear-burn models have become very popular as well.