Vented Gas Logs

• Vented gas logs produce carbon monoxide, which must be exhausted with a flue or chimney, according to Ask the Builder.com. When using vented gas logs, fireplace dampers must be kept locked or clamped in the open position, says Ask the Builder.com.
  
  

Non-Vented Gas Logs

• The burner elements of non-vented gas logs burn gas with little carbon monoxide production, according to Ask the Builder.com. Non-vented gas logs that are certified by the American Gas Association have oxygen-depletion sensors that go off when the oxygen in the room drops to a certain percentage. When this happens, the sensor shuts off the gas supply to the logs, according to Ask the Builder.com. The burners of non-vented gas logs use technology similar to that of a kitchen gas range to produce a clean, smokeless flame, according to Hearth.com.
  
  

Aesthetics

• Vented gas logs have traditionally offered a more realistic appearance. This is partly because they burn "dirty," according to Hearth.com, producing a yellow flame that effectively simulates a wood flame. In many cases, as well, vermiculite and clumps of rock wool are placed over the sand beneath the logs, which creates realistic glowing embers, according to Ask the Builder.com. According to Hearth.com, non-vented log sets now produce a yellow flame as well and also use glowing embers, but they remain less realistic than vented gas logs because of their clean-burning design and their smaller BTU rating.
  
  

Energy Efficiency

• Although non-vented gas logs consume less gas (a maximum of 40, 000 BTUs per hour, according to Ask the Builder.com), they are more energy efficient than vented gas logs because the fireplace damper remains closed. According to Hearth.com, non-vented gas logs achieve more than 99 percent efficiency. Both sources affirm that non-vented logs can provide a backup emergency heat source in case of a power outage.
  
  

Water Condensation

• Both types of gas logs produce 1.5 gallons of water for every 100, 000 BTUs of gas burned, according to Ask the Builder.com. With non-vented gas logs, this water vapor can condense on cold surfaces such as windows and in a newer, air-tight home they can create severe moisture problems in the attic and exterior wall cavities, according to Ask the Builder.com.
  
  

Prohibition

• According to Ask the Builder.com, certain states, , including Alaska, California, Massachusetts, Minnesota, Montana, New York, Utah and Colorado, prohibit the sale and/or use of non-vented gas logs. Municipalities also may prohibit the use of non-vented gas logs. Before you purchase, check with your local building department, recommends Ask the Builder.com.