'94 Avalon 745 insert questions

According to sales information he found in his house, my buddy has an Avalon 745 wood insert installed in 1994. He has the manual, but is looking for more information about the insert. It has one air control lever(secondary air), but no levers to operate any other air adjustments. Where does the air enter the firebox to feed the fire? He thought it was the bottom, but can't feel any openings or mesh down there. Does anyone have one of these or know anything about them? He has been burning it successfully for years, but he just wants to try and get more out of the insert if he can. Thanks in advance.

How big is that stove? It should be a similar design to yours Kevin. Have him call Travis Industries, the will answer any questions he has.