An air-to-air heat pump utilizes a compressor, condenser, expansion valve, and evaporator to extract and displace heat energy from air. Heat energy is stored and transferred using refrigerant. The process starts when cool gaseous refrigerant is compressed, increasing its pressure and temperature. Once in a high pressure gaseous state, it travels through a condenser to cool. As it cools, it condenses, turning it into a liquid state before passing through an expansion valve. Passing through an expansion valve causes a decrease in pressure allowing the refrigerant to evaporate. As it evaporates, heat energy is released indoors with the assistance of forced air. After cooling, refrigerant returns back to the compressor to be heated again. The process can also work in reverse in order to cool inside spaces.