What type of furnace uses a fan or blower to circulate cool air through the heat source?

The correct answer is the forced air system. This type of furnace operates by using a fan or blower to push air over a heat source, such as a heating element or heat exchanger, and then distributes the warmed air throughout the living space via ductwork. This method effectively circulates and evenly distributes heat, making it a popular choice for many residential heating applications.

In contrast, a hot water system typically operates with heated water flowing through pipes to radiators, relying on convection rather than a blower to deliver heat. A radiant system emits heat directly from a surface, such as floors or walls, without any air circulation involved. A steam system heats water to produce steam, which then travels through pipes to radiators for heating, also without utilizing a fan or blower for air movement. These differences highlight why forced air is distinguished by its reliance on a mechanical component to distribute heat efficiently.