Why is it calculated not according to the volume space, but to the area?
This approach is explained by the fact that while radiant heating air is not a heat transfer agent, so, in order to heat the room, there is no need for heating the
air contained inside. Our heaters
do not heat the air, but the
surface of the object to which
the heat rays fall. The first is the floor and walls of the room. This principle is called the direct radiant electric heating.