The furnace is the largest component of an HVAC system. It is the biggest part of the space. It’s usually in the basement since it’s considered the most central element. The primary function of a furnace is to circulate air through the heat exchanger to its air pipes. The furnace may be misinterpreted as a boiler. However, boilers are a separate class of HVAC systems.
The heat exchanger can be found in the inner part of furnaces, however that does not mean that it is a component of it. Its main function is to generate heat for the furnace.
The same can be found in the furnace, and it absorbs the heat that is absorbed when air moves across it. The refrigerant cools air, and the cool air is blown out of the pipes.
Every HVAC system is comprised of different parts which each carry out different functions. Every component depends on the one to work efficiently.