Final answer:
Gravity warm-air furnaces and forced-air furnaces are the two broad categories to describe furnace heating systems. Gravity warm-air furnaces use natural convection, while forced-air furnaces use a fan or blower to distribute heated air.
Step-by-step explanation:
The two broad categories to describe furnace heating systems are gravity warm-air furnaces and forced-air furnaces.
A gravity warm-air furnace uses natural convection to transfer heat. The heated air rises and forms a convective loop, transferring energy to other parts of the room. As the air is cooled, it contracts and sinks to the floor, creating a continuous cycle of air movement.
On the other hand, forced-air furnaces use a fan or blower to blow air over a heat source, such as a gas burner or electric heating element. The heated air is then distributed through ductwork into different areas of the home or building.