Gas logs can be retrofitted in an existing fireplace as an alternative to wood, according to the U.S. Environmental Protection Agency, which certifies heating appliances. Although gas logs do burn fossil fuels, they emit significantly lower emissions compared to firewood, according to the EPA on its Burn Wise website.
Gas logs can be vented or vent-free. Vented logs, which operate with an open chimney flue or damper, simulate a wood-burning flame. Vent-free logs won’t give you the roaring fire effect, but provide a little more heat and may have a thermostat to maintain room temperature.