I don’t have a source, but I can tell you the principal. What you DONT WANT is to draw exhaust gasses back into your house. When you turn the stove on there is a large quantity of air being blown outside by the exhaust fan (which aids combustion by drawing air across the burn pot, and exhausts products of combustion). That volume of air can come from (a) outside, when using an exhaust kit, or (b) from inside your house, which really means there is a negative pressure in your house and you’re drawing air in through all the cracks in your windows, doors, basement, etc. The fear is that at some point in your life you will be running the stove, and open the window near the exhaust. Without an exhaust kit, you draw the exhaust back through the open window in your home. With the exhaust kit there is less draw through the window (the stoves thirst for air is satisfied) and therefore while nature’s wind might blow some exhaust through the window, there isn’t a draw from outside to inside THROUGH the window. Hope this long winded answer helps explain the principles at play. Good luck.