Abstract: A rotary regenerative air preheater has a preliminary heating stage for the cold air, before it reaches the regenerative mass, constituted by recuperative heating surfaces provided within the ducting which brings the cold air to the regenerative mass and which are heated by exhaust gas which has passed through the regenerative mass but has lost least heat to that mass. The surfaces take e.g. the form of tubes passing through the channel and gas is guided into these tubes by a gas-catching wing extending to close to one face of the regenerative mass.An embodiment of each of a rotating-and a stationary-mass preheater are described.