Which of the following does NOT describe a characteristic of radiant heating systems?

Radiant heating systems are designed to provide warmth through the direct transfer of heat from a surface to a person or object, rather than through air circulation. Option A is correct because radiant heating does not rely on ductwork for heat distribution; instead, it typically operates through methods such as embedded hot water pipes in floors or electric heating cables.

The remaining options highlight key characteristics of radiant heating systems. Option B is accurate as these systems can indeed be installed under floors, allowing heat to rise naturally into the living space. Option C is also valid because radiant heating systems are known for providing even heat distribution across a room, minimizing cold spots. Lastly, option D reflects how radiant systems can operate either with hot water (in hydronic systems) or electric coils, both of which are common methods of producing the heat that radiates into the space.

Thus, the distinction of not using ductwork clearly defines why option A does not describe a characteristic of radiant heating systems.