This system cycles air into the CHE where it passes over fins in the passage reducing the   temperature of the fins which removes the heat. On the inside loop, the air in the case is brought   into the CHE raising the temperature of the fins. The heat is passed from the inside loop to the   outer loop via the fins (passive connection). The heat dissipation capability depends on the   position of the case (stand alone, positioned against wall, stacked). It works most effectively   when there is a temperature differential between the inside and outside of at least 20°C.