The answer to 'what is heat exchanger' is a critical component in a furnace or air conditioner that transfers heat from one medium to another. It is responsible for transferring the heated air from the combustion process (in a furnace) or the refrigerant cooling process (in an air conditioner) into the air that is distributed throughout the home. The heat exchanger is essentially the 'heart' of the HVAC system, as it is the main mechanism for heating or cooling the air.
The heat exchanger is typically made of metal, often steel or aluminum, and is designed with a large surface area to maximize the heat transfer. As the hot air or refrigerant passes through the heat exchanger, it heats up the metal, which in turn heats the air that is blown over the exchanger and distributed through the ductwork. This process allows the HVAC system to efficiently heat or cool the home without the hot or cold air directly contacting the living space.