Vented Gas Logs (Direct Vent)
Vented gas logs have become more popular than Ventless gas logs mainly because they have a more realistic/natural looking flame. Unlike ventless gas logs, the flames wrap around the vented logs like real wood, increasing the resemblance of a real fire. You have more freedom with vented gas logs when it comes to positioning the logs, because the flame actually comes in contact with the vented logs. The heat output is similar to burning wood, so vented gas logs must be installed in a fully functioning wood burning fireplace.
Ventless Gas Logs (Vent Free)
Ventless gas logs produce more heat than vented gas logs and are therefore better at heating. The heat from the fireplace circulates back into the room instead of out the chimney. This creates a much more efficient source for heat. Vent free gas logs do not require being installed in a fully functioning wood fireplace. They are also designed to burn cleanly. However, they cannot be re-positioned like vented gas logs. If the flame touches the logs, soot and exhaust gases will be produced. The logs need to remain in the position specified by the manufacturer. An Oxygen Depletion System measures the amount of oxygen in the room and turns the burner off before the oxygen in the room gets to low. An ODS is required to use with ventless gas logs. Please check your local codes as certain states and cities do not allow the use of these logs.