Abstract: The invention concerns the design arrangement of the cap for the inlet of fluid into the fluidization bed which is heated or cooled by the methods described in U.S. Pat. Nos. 3,897,546 and 3,908,284. The cap is formed by an inlet pipe closed at its upper end on which are formed two or more mutually separated chambers, while in this pipe a number of holes is drilled for the inlet of fluid into the chambers. Into these chambers a number of holes are drilled for the outlet of fluid from these chambers into the fluidized-bed. The vertical distance of the inlet holes from two neighboring chambers of the cap either equals or is smaller than one and one-half times the height of the heat exchanger situated in the particular fluidization bed formed between these two neighboring chambers of the same cap. The caps were used for the inlet of the combustion air into a fluidized-bed combustor, while the pressure drop of the lower part of the cap did not exceed 10% of the pressure drop of the upper part of the caps.