In which mode does an air-to-air heat pump extract heat from the outside air?

In heating mode, an air-to-air heat pump extracts heat from the outside air and transfers it indoors, even when the outside temperature is relatively low. This is made possible through the refrigeration cycle, where the refrigerant absorbs heat from the outside air, evaporates, and is then compressed, leading to a significant increase in temperature. The heated refrigerant is passed through the indoor coil, releasing heat into the living space.

This is the primary function of a heat pump in the winter months or cold climates when heating is required. It efficiently utilizes ambient outdoor air to provide warmth indoors, making it an energy-efficient heating solution compared to electric resistance heaters.

In contrast, in cooling mode, the heat pump operates in reverse, removing heat from indoors and transferring it outside. Defrost mode serves to prevent ice build-up on the outdoor coil by temporarily reversing the system, while idle mode indicates that the heat pump is not currently in active operation to heat or cool the space.