Whenever something burns, carbon monoxide is present. Direct-vented gas fireplaces use a sealed combustion venting system that expels all combustion by-products to the outside, including carbon monoxide.
However, some older gas fireplaces and all gas log sets installed into a wood-burning fireplace use a different type of vent system that is not entirely sealed up. This "silent killer" is odorless, tasteless, and colorless. The best defense for a homeowner? Have your fireplace professionally serviced regularly, and ensure you have a carbon monoxide detector with fresh batteries.
