A method for measuring mass changes of a heat exchanger bank (1, 2, 3) or the heat exchangers thereof of a steam boiler, which heat exchanger (4) is supported by hanger rods (7) to support beams (5,8) above the steam boiler, wherein at least one hanger rod (7) of at least one heat exchanger (4) is connected a lower measuring element (9) and an upper measuring element (10), and the changes of the measuring length (X) between the measuring elements (9, 10) is measured by a measuring instrument (15) connected between the measuring elements (9, 10) for measuring the mass changes of the heat exchanger (4). The measuring instrument (15) may be attached in between the measuring elements (9, 10) and the change in the measuring length (X) is measured by the deformation of the measuring instrument (15). A connecting member (11) parallel to the hanger rod (7) may be located between the measuring elements (9, 10), which connecting member (11) relays the change in the length to the measuring instrument (15). An elastic member (16) may be attached between the measuring element (9) and the upper measuring element (10).