Question about wood stove insert set up - Vents in bedroom of second floor above catalytic wood stove insert

[Mattman079]

I have a question I am hoping someone can figure out based on probably not enough information. My wife's parents house has a catalytic wood stove insert in their living room fireplace. Directly above their living room is the master bedroom and in the master bedroom on the same wall above the wood stove there are two large grates. When they run their wood stove, it some how uses the vents to heat up the master bedroom as well as the living room. Does anyone know how they were able to do this? It works well and I wanted to use the same process in my house to help heat the second floor, however, my father-in-law passed away and he was the only one who was involved when they were originally building the house. If anyone has any ideas of how this might have been done or any suggestion on ways to find out I would be grateful!