Are ventless gas fireplace inserts energy efficient?

Ventless gas fireplace inserts convert 70 percent or more of gas energy into heat. Green building advocates argue the energy efficiency rating is offset by side effects of the exhaust fumes staying in the room, including health concerns and too much condensation in the room.

Experts debate the safety of gas fumes in the home, with some saying the effects are negligible and others saying they are a health concern. Newer ventless gas fireplaces and inserts have sensors that automatically shut off the gas if high carbon monoxide levels are detected, but the exhaust fumes still remain in the room and create condensation.