So you bought a vent free gas log or a vented gas log to retrofit your fireplace from wood burning into “clean” gas burning, and you wonder can I plug a gas fireplace chimney?
You read all about how your “clean” burning gas log can operate at 99% efficiency, because it doesn’t need to be vented through a chimney to the outside. Now, you are wondering how to plug a gas fireplace chimney, so you can keep all that heat in the house?
Honestly, I don’t know how installers or manufactures of gas log fireplaces can in good conscience sell gas log retrofits anymore. Vented gas logs are a setup for drafty rooms and high gas bills with no heat to show for it. Vent free gas logs are promoted as “clean burning”, even though they have been proven by a University of IL study that shows they put high levels of NO2 fume contaminants into your home.
Just google “vent free gas log dangers” and you will see hundreds of articles on that topic. Some US states have banned them entirely, for good reason! You will notice all the “Pro” gas log articles are by places that benefit from you buying one, and the “Con” articles are health agencies or building science agencies.
Personally, If I bought a house with a gas log of any kind, the first thing I would do is pull that gas log out and plug a gas fireplace chimney afterward.