Abstract: An evaporator assembly for a heat transfer unit comprises a sealed thermally conductive container and a duct mounted in the container. Channels are formed between the walls of the duct and those of the container and thermal transfer fins are attached to the inside surfaces of the walls of the container and located in the channels. An evaporator extends transversely across the width of the duct and a defrosting heater bank is located downstream from the evaporator in the duct. Suitable fans and a drive motor are mounted at one end of the duct to circulate air or other gas through or across the evaporator, through the duct, and through the channels. During use of the assembly, heat is transferred from the container walls and the fins to the circulating air and the heat is then extracted from the air or gas by thermal transfer through the evaporator. The assembly provides a buffer between the heat source and the evaporator in order that the evaporator may operate in a near moisture free environment.