Two Types

• You'll need to determine what kind of vent the fireplace has. Two standard types of vented fireplace are available for purchase and installation: the direct vent and the natural vent, or B-vent. The natural vented fireplace is the traditional fireplace, featuring a vent that leads smoke straight up through a chimney and out into the environment. This is the model installed on older homes. Newer homes feature a direct vent system that uses a series of pipes and vents. Unlike natural vent fireplaces, which require chimneys at the roof of a house, the outlet for a direct vent can lead to the side or the top of a house.
  
  

Combustion Air

• The most important thing a fireplace must do is burn. Whether gas or wood, air is required for combustion of the material and the generating of heat. Different types of vented fireplaces get their air from different places. The natural vented fireplace draws air from the room, and this air feeds the fire and radiates heat out into the room after burning the oxygen. Because of this, natural vents work better in homes with good airflow. New homes have a more insulated and airtight design and do not have the air to spare without making the room uncomfortable. Direct vents are better here since they feed the fire air from the outside using an inlet pipe.
  
  

Radiation

• Both direct vent and natural vent fireplaces emit heat through radiation, although they may not do so equally. Because natural vent fireplaces draw oxygen from an enclosed space, they tend to burn slower and lower than direct vent fireplaces, which feed their fire a constant source of fresh air from the outside.
  
  

Exhaust

• The drawback to a fireplace is exhaust. Fires create not only smoke, but also scorched particulate matter that is lifted into the air by radiating heat. Direct vent fireplaces use the exchange of air to suck the smoke and particles out through a vent located on the top or side of the unit. Natural vents use a combination of suction and heat radiation from the fire to push smoke up through the chimney for removal.