Yeah, and don’t forget lung illnesses, mold and window rot! The amount of water released by an unvented gas burner is pretty staggering, and it condenses on windows and other surfaces causing paint failure, mold, and rot throughout the home. And high humidity also increases the lethal potential of lung diseases like pneumonia.
As for efficiency, I was going to install a gas burner in my fireplace until I did about five minutes of research on the economics of it. I installed a wood burning insert instead and I’ve been very happy with that. (Although admittedly I enjoy chopping wood.)
