Question: I am considering purchasing a vent-free gas fireplace. What happens to the carbon monoxide ? Are there any other health concerns that I should be aware of regarding gas fireplaces? Answer: Any gases from a vent-free fireplace go right back into the home, similar to a gas range. Although they burn quite clean, there is still some CO and CO2 produced. For this and other reasons, vent-frees are not designed for full-time use..just for a few hours per days. Used this way in most areas, there will not be any problems. Also, regarding health concerns, if anyone in the house has asthma and/or other sensitivity problems then a vent-free may not be the best idea.