I have always been aprehesive about flexible gas lines. The home I just moved into has a new ventless natural gas fireplace. The gas comes into the fireplace via a flex line which is connected from the main gas line nearby. My question is... are the flex lines rated and approved to be used INSIDE the firebox itslef? (connected to the burner pan). It is a small fireplace and does not get to hot, however I was wondering what the rating on these things are when it comes to nearby flame.