When oil or gas auxiliary heat is utilized, where must the indoor refrigerant coil be located?

The indoor refrigerant coil must be located in the outlet stream when oil or gas auxiliary heat is utilized because this positioning allows the warm air to be effectively heated as it exits the heat pump system. By placing the coil in the outlet stream, the warm refrigerant can transfer its heat to the circulating air efficiently, maximizing the heating capacity and ensuring that the home receives the appropriate amount of warmth.

When auxiliary heating is employed, it typically provides additional heat to support the heat pump during colder conditions. Having the indoor coil in the outlet stream ensures that the air being circulated back into the living space is already pre-heated, resulting in more efficient operation and comfort in the home. This placement enables a more effective integration between the heat pump and the auxiliary heat source, ensuring that the desired temperature can be achieved without unnecessary strain on the system.

The other options do not align with the operational principles of heating in a residential air-to-air heat pump system and would lead to inefficiencies or inadequate heating. Therefore, the correct answer emphasizes optimal placement for effective heat transfer and system performance.