A direct vent fireplace or fireplace insert is one that is has its exhaust vented outside through a vent tube that is connected to a chimney or wall.
Direct vent gas fireplaces are the currently the most popular choice used because of their many advantages. The most efficient and safe of all gas fireplace options, direct vent fireplaces work using a vent tube through an outdoor wall in your home. One tube exhausts the fumes from the fireplace out of your home, and in sealed combustion models, brings combustion air from outside the house as well - allowing maximum efficiency and safety because the air within the home is left completely undisturbed. This option virtually eliminates heat loss, and causing no drafts. On top of that, they are tested to operate at approximately 90% efficiency.
If you are looking for an extremely efficient type of gas fireplace, a direct vent fireplace will work very well and keep the air in your home undisturbed. Make sure you have the ability to install the venting properly, and consult a professional with assistance in installation.