The paper deals with methods to establish a source function describing the density of hydration heat. As a thermal loading, the function results in nonhomogeneity of the heat conduction equation to be solved in order to find the temperature field inside a concrete block on curing. On the background of existing methods a new one is proposed to establish the source function. Analytical form is given and a way to derive suitable test coefficients is described. Appropriate system of conditions is shown and its solvability is discussed. Illustrative examples are given.