(57) A hot air drier has a heat exchanger (25) for transferring heat to a first flow path (45) from a second flow path (30). The first flow path (45) has a blower unit (14) and an electrical heater (22) for pre-heating outside air and discharging it into a confined space where clothing or body drying is carried out. The humidified air is drawn out of the space and into the second flow path (30). A motor (40) controlled by a temperature or humidity detector (70 operates a pair of fan impellers (41,42) at the entries of respective passages through the heat exchanger. During a start-up phase the motor (40) is not operated and a by-pass circuit allows the blower unit (14) to re-circulate air through the confined space so that the air temperature rises rapidly to optimum drying conditions prevail.The motor (40) is then operated. The drier operates economically without discharging hot humidified air into the surrounding room.