Vented gas logs are the most popular type of gas logs as they often have a more realistic and natural looking flame than vent free gas logs. The flames wrap around the logs like real wood, increasing the resemblance of a real fire. Unlike vent free gas logs, vented gas logs are able to be repositioned since the flame actually comes in contact with the logs. The heat output is similar to burning wood, so vented gas logs must be installed in a fully functioning wood burning fireplace. This limits their heating efficiency as the majority of heat is lost as it goes up the chimney.
Vent free gas logs (also known as ventless gas logs) are often preferred for their heat output, which greatly surpasses that of vented gas logs. The heat circulates the room instead of going up the chimney, creating a highly efficient heat source. Vent free gas logs do not have to be installed in a fully functioning wood fireplace and are designed to burn cleanly. However, they cannot be repositioned like vented gas logs. The logs need to remain in the manufacturer’s specified position – if the flame touches the logs, soot and exhaust gases will be produced. Vent free logs are required to have an ODS (Oxygen Depletion System) that measures the amount of oxygen in the room and turns the burner off before the oxygen in the room reaches an unsafe level. Be sure to check local codes as certain states and cities do not allow the use of vent free gas logs.