When a heat pump is operating in heating mode, how does the indoor coil function?

When a heat pump operates in heating mode, the indoor coil functions as a condenser. In this mode, the heat pump extracts heat from the outdoor air and transfers that heat indoors through the indoor coil. The refrigeration cycle is reversed, causing the refrigerant to absorb heat as it evaporates in the outdoor coil and releases that heat as it condenses in the indoor coil.

In heating mode, the refrigerant enters the indoor coil in a gaseous state and, as it passes through the coil, it releases heat into the indoor space causing the refrigerant to condense back into a liquid state. Simultaneously, this process raises the temperature of the indoor environment, providing effective heating.

The option identifying the indoor coil as an evaporator pertains to the cooling mode of operation, where the indoor coil absorbs heat from the indoor air, causing the refrigerant to evaporate. In heating mode, the function of the indoor coil completely shifts away from absorbing heat and focuses on releasing heat, reinforcing its role as a condenser.