Flapper At Combustion Chamber Door Bottom PF100

My PF100 pellet furnace has what appears to be a small damper flapper at the bottom outside of the combustion chamber door bottom. Why is that there?

Got the answer by emailing Harman:
It supplies additional combustion air to the firebox and also creates an air wash for the glass in the ash door. Most of the combustion air is supplied through the back draft damper on the rear of the feeder body.