Where does the air come from in the firebox?

The firebox introduces combustion air through 4 sources. 1) Immediately beneath the door opening below the window is a Lower Primary Air Orifice. 2) The primary air inlet control (center control lever) brings air into the firebox and controls the rate of burn and amount of heat the stove radiates. 3) The high burn duct control (right control lever) provides additional air for maximum burn rate. 4) The secondary air tubes at the top of the firebox. There are also small openings under the hearth bricks that circulate the combustion air within the stove.