Gas logs that burn clean and produce a hot blue flame are known as vent-free, unvented, ventless, or non-vented gas logs. These logs
lack the aesthetic beauty of vented gas logs that burn with a natural yellow flame but burn much hotter and therefore produce more heat. Vent-free gas logs do not need a ventilation system to vent the products of combustion because the gas is fully burnt into heat.
Some vent-free gas log sets come with blowers that actually blow the heat directly into the room. Since the damper can be fully closed while in operation, no heat escapes through the fireplace. All vent-free gas logs come with an Oxygen Depletion Sensor which will immediately shut off the appliance if the oxygen level reaches 18%. Normal oxygen levels are 21%, and this feature that comes standard with every vent-free gas log set insures the safety of the appliance.
Vent-free gas logs are allowed no more than 40,000 BTUs. Although most vent-free gas logs are not approved for bed or bathroom use, those that are are limited to 10,000 and 6,000 BTUs respectively. The flame produced by these logs are extremely hot and even if the minimum required clearance is met, the mantle and surrounding walls may still be warm to the
Vent-free gas logs can be installed in an existing fireplace although it is not required. Some homeowners without a fireplace choose to install the logs in vent-free fireboxes, much like prefab fireplace fireboxes, that have no connection to a chimney. The latter method is highly debated. Codes may change in the future regarding the legality of installing vent-free gas logs in prefab fireboxes, but this change would not affect units previously installed.