Abstract: The preheater for a clothes dryer preheats ambient air taken into the dryer by heat transfer from hot air discharged from the dryer, thus reducing the energy requirements of the dryer. The preheater includes a box with a heat conductive partition defining a first passage for flow of ambient air into the dryer and a second passage for flow of hot discharge air from the dryer reverse to the ambient air flow so that there is a relatively high temperature difference between the passages for effective heat transfer. Heat is transferred through the partition from discharge air to ambient air, and the partition has a serpentine configuration for increasing its heat exchanging surface area, thus improving heat transfer.