other fluid to be heated enters the heat exchanger through an inlet duct and is discharged after flowing over the heated material 16 through an outlet duct to which an induced draft fan is usually connected after passing over the heated material the cool air absorbs heat therefrom and is then directed to a place of ultimate use a cylindrical housing encloses the rotor in spaced relation thereto to provide an annular space 18 therebetween sector plates 26 intermediate ends of the rotor and the adjacent housing structure lie intermediate spaced apertures that admit and discharge the streams of gas and air in order that the streams of gas and air do not bypass the rotor it is customary to affix flexible sealing means 30 to the end edge of the rotor to confront the adjacent surface of the rotor housing to preclude the flow of fluid therebetween in a standard heat exchanger of the type herein defined the hot has enters the top of the heat exchanger and transfers its sensible heat to the heat absorbent material of the rotor before it is discharged as cool gas from an outlet duct inasmuch as the inlet for the cool air lies at the bottom of the heat exchanger adjacent the cool gas inlet the bottom of the heat exchanger is termed the 34 cold 34 end while that lying adjacent the hot gas inlet is called the 34 hot 34 end it will be evident that the 34 hot 34 end of the rotor is subject to maximum thermal variation while the 34 cold 34 end is being subjected to a lesser amount thus maximum thermal expansion of the rotor housing and the adjacent end of the enclosed rotor occurs at the top.