Direct vent gas was invented by Heat & Glo, the number one brand in gas hearths. This exclusive technology is also used in Quadra-Fire and Heatilator fireplace products. This sealed system technology provides safe, convenient and consistently beautiful fires, with the flip of a switch -- every time. Direct vent technology uses outside air for combustion and expels by-products like carbon monoxide, nitrogen dioxide and excess moisture. Terminated to the outside, either vertically through the roof or horizontally through the wall, direct vent technology makes it possible to install and vent a gas fireplace, insert or stove in almost any room. This saves energy and delivers warmth and comfort where you need it most. Direct vent technology revolutionized fireplaces, making them safe and convenient. It is the most requested type of technology for gas fireplaces, inserts and stoves today