Vent-free heaters are commonly considered safe and must pass tests performed by national safety organizations before they can be marketed to the public. Vent-free heaters that are properly installed and maintained do not affect air quality.
Vent-free heaters typically come with a oxygen depletion sensor that alerts homeowners if the oxygen level drops to an unsafe level. Vent-free heaters come equipped with a safety valve designed to turn the gas off to the unit in the event of a malfunction or if the pilot burner goes out. Vent-free heaters are 99.9 percent energy efficient, and they are the number one supplemental heat source for Americans as of 2015.