Moisture

• According to AskTheBuilder.com, natural gas emits about 1.5 gallons of water per 10,000 BTUs of gas used. Since the air vents inside the home, this moisture can get into walls and cause problems such as mold.
  
  

Legality

• As of 2010, ventless gas logs are illegal to install in the states of California, Wisconsin and Montana. In addition, some local counties and cities, such as New York City, have banned vent-free gas logs, even though state law allows them.
  
  

Aesthetics

• The technology used to make vent-less gas logs highly efficient produces a dark-blue flame instead of the traditional orange flame, a downside for people who want to use this type of heater for decorative purposes.
  
  

Price

• The typical vent-less gas log system will run about $800 to $2,400 -- much more than a vented log system, which usually ranges from $300 to $600.
  
  

Tip

• Some companies make vent-less gas logs with a ceramic lining around the combustion chamber that turns the blue flame to a bright yellow.