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Direct vent units use a co-axial vent pipe for operation. In other words, a small pipe within a larger pipe. The small pipe vents exhaust gases to the outdoors and the larger pipe draws combustion air inside for operation. These units feature a fixed pane of glass that seals them from the living space, but is easy removed for cleaning. They may be vented vertically or horizontally, making them very flexible units for a variety of installations.
These units are generally a high efficiency, clean burning design that gives good supplemental heat to a room. They are also available in a wide variety of styles and sizes. The downside to these models is that the glass window can get very hot and cause burns if touched. They must also be installed according to exact specifications to avoid clouding of the glass.
Natural vent units are actually the same as B-vent. The term is used interchangably by manufacturers. B-vent refers to the grade of vent pipe they use, while natural vent refers to the manner in which they operate. They use a single 3-6 inch diameter vent pipe that must be vented vertically. These units are open to the room and use combustion air from inside the house for operation.
These units are lower efficiency and are made more for ambiance than supplemental heat. Being that they are open to the room, they appear to be more realistic than a direct vent. B-vents are only available in a few standard sizes and are becoming fewer and fewer as direct vents begin to dominate the market.
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