Abstract: A regenerative gas-to-gas heat exchanger having a plurality of superposed spaced, parallel beds of confined metal flakes adapted for gas flow therethrough; four gas plenums surrounding the beds, each plenum communicating with one side only of all the beds; means for supplying a relatively hot gas to one plenum, means for supplying a relatively cold gas to an opposite plenum, each of the remaining plenums communicating with a separate outlet; and sliding gate valve means in each plenum adjacent one side of the beds, means for moving the gate valve means to a first position and to a second position for controlling the directions of gas flow and alternately extracting and releasing heat therefrom.