An Innsbrook Direct-Vent Insert turns your drafty wood-burning fireplace into an efficient gas-fired heat source. A wood-burning fireplace sends more than half of its heat up the flue, creating negative pressure in your home, which draws in outside air through gaps in doors and windows that actually makes your home colder. A wood-fire can also create ash and fumes that dirty your home and aggravate your allergies. The Innsbrookâs direct-vent system uses readily available 3-inch flexible co-linear vent pipes. One draws air from outside your home, and the other sends flue products directly outdoors. The flexible metal venting allows the insert to install easily in a site-built or manufactured fireplace. The Innsbrook is available in three sizes to fit most wood-burning fireplaces.