What is the difference between Fire Glass and Gas Logs or Lava Rocks?

Adding any type of decorative media onto an open flame reduces the flame temperature as it comes into contact with the media, resulting in lower burn efficiency and less heat. Fire Glass, on the other hand, has very little effect on the flame efficiency and resulting heat output because combustion takes place above the glass, not below it. Thus the flame is not cooled or impaired, resulting in maximum heat output.