This allows the air to drop down and form a barrier behind the glass. Since the air entering the stove is relatively cool, it falls quickly and is sucked into the hot combustion zone at the base of the fire. When reloading this type of stove, be careful about placing very large logs in the very front of the firebox. Such a log could close off the airflow to the fire. This burning creates intense heat, which is then transferred to the stove and room.
All catalytic stoves employ a bypass damper, which is opened when starting or reloading the fire.
When this damper is opened, the smoke can escape directly up the chimney. When closed, the smoke is routed through the catalytic converter. A decent fire MUST be built previous to closing the bypass damper. Catalytic converters require temperatures of 500 degree in order to start doing their thing. Take care not to let the fire burn down too low.