What type of heating does a forced-air system primarily use?

A forced-air heating system primarily utilizes circulated air as its method of heating. In this system, air is heated by a furnace, which can burn fuel or use electric elements, and then the warmed air is pushed through a series of ducts and vents into various spaces within the building. This circulation of heated air allows for rapid and efficient warming of rooms, making it a popular choice in many residential and commercial heating systems.

The other options do not accurately describe the core functionality of a forced-air heating system. Hot water and steam systems, for instance, rely on liquid or vaporized water to transfer heat through radiators or pipes, which is fundamentally different from the air circulation method employed by forced-air systems. Electric heating, while it can be a component of a forced-air system, does not encompass the overall principle of how a forced-air heater operates, as it does not specifically describe the medium through which heat is distributed. Thus, the choice of circulated air correctly identifies the primary heating mechanism within a forced-air system.