Direct Vent Gas Fireplaces
Coaxial vent system of a pipe inside a pipe (generally 4"/7") the inside pipe is for exhaust while the outer pipe brings in outside air for combustion. The design of these stoves allows for a completely sealed system that does not compromise the inside air quality of your home. It also lets you vent a product horizontally (great for when an appliance is installed on an outside wall). Direct vent appliances are usually limited to a length of 40ft (with a maximum horizontal length of 20ft) that will allow an appliance to function properly.
ZRB46 featured above.