The best example for radiant heat is the sun, source of all life on our planet. While the temperature inside the sun is almost 16 Million °C the surface temperature is “only” about 6.000°C. And although the sun is about 150 Million km away we can still feel the warmth of the infrared radiation. The kachelofen gets around 1.000°C inside and around 100°C on the outside. The energy is the same natural radiant heat with the same wave length and at a level human beings need for perfect bodily comfort.
All life on this planet evolved and depends on the natural radiant heat provided by the sun. Imagine the sun shining on a stone wall all day long. After sun set you pass that wall and immediately you can feel the stored radiant energy. The kachelofen has exactly the same effect on your house: all day long the energy of a fire burning for only about 1 hour is emitted over the surface and stored in the structure of your house. After some time the floors, walls and ceilings start to radiate back the energy. We call that activating the structural mass of the house. Now the warmth comes equally from all sides.
Mark Twain says about the kachelofen: “All day long and until past midnight all parts of the room will be delightfully warm and comfortable […] in a German room one is comfortable in one part of it as in another. Nothing is gained or lost by being near the stove”.