Abstract: A microwave furnace having an impervious housing with an inlet and an outlet and a fan or blower for inducing within the housing a moving air stream. Supported within the housing within the air stream is a body of microwave lossy material. Also within the housing upstream of the body of microwave lossy material is a microwave source and a transmission line for transmitting the microwave energy from the source to the body. The body is configured with respect to the cross sectional shape of the air flow path such that the moving air passes through a relatively small gap between the body and the inner surface of the housing, thereby affording sufficient residence time for the air to be heated by radiation from the body.