What is a characteristic of an unvented room heater?

An unvented room heater is characterized by its freestanding, nonrecessed design. This means it does not need to be built into a wall or structure, allowing for greater flexibility in placement within a room. Because it is designed to operate without an external venting system, it can be positioned in various locations without the need for ducts or flues to exhaust combustion gases outside. Unvented heaters typically rely on the ambient air in the room for combustion and do not require external ventilation, making them distinct from vented models that must exhaust combustion products outside.

While the other characteristics mentioned in the options refer to different types of heating appliances or requirements for vented heaters, they do not accurately describe unvented room heaters. Understanding these specific traits is essential for ensuring compliance with safety regulations and effective heating practices.