Heat can be transmitted through EM radiation (of all frequencies, but IR is predominant for temperatures we're accustomed to) but also by direct contact between materials. For typical temperatures, radiation doesn't transmit much heat. Vacuum makes for a pretty good insulator. If you want to remove 20kW of heat from a small space, you'll need to do most of that removal by transferring the heat to a fluid of some kind, e.g. by putting it into the air.
To see the difference in practical terms, pick an item that's noticeably warm, but not hot enough to burn you. Hold your finger very close to it. The heat you feel there is radiated. Then touch it, and feel the heat that's conducted through touch. You'll feel much more heat with the latter.