If your fireplace doors are shut oxygen cannot reach the flames.
Gas fireplace doors open or closed for heat.
Allowing your fireplace doors to remain open will promote better airflow.
99 of the time your fireplace doors should be open when you are burning a fire.
If you close the doors the flames pull towards the glass where it can impinge and shatter the glass.
Ceramic glass doors a masonry fireplace and do not care about any heat coming into your room then it is ok to burn a fire with your glass doors closed.
Large 10 class a metal chimney required hefty 1000 lbs of masonry firebox unsealed good radiant heat and open to the room no fans or accessory heat ducts.
This results in a dull blaze with little heat output.
Open no glass doors like isokern or firerock with add on gas burning unit fake ceramic logs.
It is still an open hearth fireplace which is susceptible to aerodynamics.
In the off chance you have.
Designed as a surface mount these track free doors sit outside the fireplace opening against a flat surface and help reduce.