A heater damper is a valve on a heater that controls the airflow allowing for heaters to operate more efficiently. Dampers are used on gas operated heaters, as they control the airflow and gas exhaust, which is not applicable to an electronic powered heater.
The damper works by opening prior to igniting the pilot light. Once the damper opens and the pilot sequence is complete, the burner will ignite in the heater and the exhaust gas will travel out of the heater. The damper closes once the pilot is lit; this eliminates airflow through the flue tube, which reduces heat loss and optimizes efficiency.