Generally speaking, a convector heater generates and circulates warm air currents without any obvious sign of heat glowing red from the heater. They are ideal for heating “air spaces” and the things in the room.
A radiant heater generates heat-waves from a heated surface (often glowing red) and this heat-wave heats objects in its path. Waves can be short, medium or long. Short are more intense but lose their strength over shorter distances, long are less intense (gentler) and maintain their strength over longer distances. They are ideal for heating “objects” within the heat wave.
In a convection heater, heated air convects around a room and provides warm air currents. The colder air near the floor is drawn through the heater. This heated air will circulate up and then down and around a room. Walls, carpets and furniture, as well as humans, will eventually feel warm due the convected warm air current transferring its heat. This is determined by the size, shape and insulation qualities of a room, the number of air changes taking place, the size/setting of the heater, and location of the heater.
In a radiant heater, heat-waves are emitted directly from the heater and these waves heat all objects in their path. This is similar to light waves, think of a torch light and anything inside the light waves receives light, anything outside remains dark. Radiant heaters can be ‘aimed’ directly at the object to be heated. This is a more efficient way of heating people directly in large open spaces with lots of air changes.