What happens in a heat pump during heating mode?

In heating mode, a heat pump operates by extracting heat from the outside air, even when temperatures are low, and transferring that heat indoors to warm the living space. This process utilizes the principles of thermodynamics, specifically the refrigeration cycle.

The heat pump contains a refrigerant that absorbs heat from the outside air as it evaporates in the evaporator coil. The compressor then raises the temperature of this refrigerant to move it indoors, where the heat is released into the living space through the condenser coil. This method is energy-efficient compared to traditional heating systems that rely on electric resistance heating or combustion methods because it essentially moves heat rather than generating it from raw energy sources.

In contrast, other options incorrectly describe the heat pump's function. For instance, removing heat from indoors and releasing it outdoors describes cooling mode. Using only electrical resistance heating does not apply to heat pumps in heating mode, as they primarily rely on heat extraction from outdoor sources. Cooling indoor air effectively corresponds to the heat pump's operation in cooling mode rather than heating mode. Thus, the correct understanding is that, during heating, a heat pump extracts heat from outside air and transfers it indoors.