Gas inserts are designed to increase a fireplace's efficiency. An insert is basically a fireproof box that's surrounded by steel or cast iron and fronted by insulated glass, creating a closed combustion system.
Gas logs offer the ultimate in realism and convenience. Vented gas logs operate in a traditional fireplace with an operable damper, which must be open while the logs are burning. Vent free gas logs do not need to be vented to the outside and offer greater heat and efficiency.