A Radiant Heating System emits heat similar to that of the sunshine. If you were to stand outside on a hot summers day then you would feel warm and comfortable as the Radiant Heat from the sunshine is traveling through the air and warming your body temperature. However, if a cloud were to prevent the sunshine from reaching you then you would immediately feel colder, even though the air temperature hasn't changed, this is because the cloud is preventing the Radiant Heat from reaching your body.

This works the same way if you think about a Radiant Heating System in an office environment. The Radiant Heat that is being emitted from the Radiant Heating System travels through the air and heats its surroundings of a lower temperature.