Final answer:
The indoor coil in a Dual Fuel System must be located in the airstream of the indoor unit, which is usually above the furnace for upflow systems or below for downflow systems to ensure efficient operation.
Step-by-step explanation:
In Dual Fuel Systems, the indoor coil must be located in the airstream of the indoor unit, typically either above the furnace in an upflow application or below it in a downflow setup. The positioning of the coil is critical as it is an interface between the heating and cooling components of the system. When part of a heat pump system, this coil acts to either release heat into the home during the winter or absorb heat from the home during the summer. Therefore, proper installation and location of the indoor coil are essential for efficient energy use and optimal performance of the dual fuel system.