Ceiling-mounted radiant heaters can be efficient heating choices for small spaces or rooms that are used rarely. However, radiant heaters have poor efficiency when heating larger spaces.
Radiant electric heaters work by emitting infrared radiation that is directly absorbed by objects and people in the path of the beam. This allows them to heat specific people or small areas quickly, meaning that they can often be run for a shorter time than other heaters and thereby use less energy. This property is also what makes radiant heaters inefficient for heating large spaces, as the air in the room is not heated efficiently and cannot circulate heat well to areas outside of direct line of sight to the heater.