Hi All, I have not been able to find any documentation on how the Fireplace Xtrordinair - firebox air intake system functions and where the air is pulled from. It is not even discussed in the Travis Industries installation manual. My Fireplace Xtrordinair is about 20 years old. I would like to inspect the firebox intake. There is no duct piping to the outside of the house. I suspect that air may be pulled from the space between the inside and outside chimney pipe space. The firebox is not burning well. It may be caused by clogged catalitic converter but I have the bypass open. I am considering removing the catalitic converter since I prefer to burn with the chimney wide open and full air intake . Thank you in advance for any insights or advance you may be able to provide.