The axial fans connect to the domestic control box facing out. They keep the control box contents (burner, blower motor and electrical components) cool.
I need a little more information in order to get you the correct axial fan. Please ask another question and include the manufacturer, model number and serial number of your equipment. If you do not have this info, I need to know the hole centers and fan blade direction (clockwise or counterclockwise) of the fan you are trying to replace.