Abstract In view of the importance of the condensation-induced water hammer in various engineering fields, this study performed an analytical modeling and numerical simulation to obtain the map of the onset of the condensation-induced water hammer. Two linear boundaries were experimentally observed for the transitions between no condensation-induced water hammer and non-periodic condensation-induced water hammer and between non-periodic condensation-induced water hammer and periodic condensation-induced water hammer. The analytical modeling based on the energy balance equation was conducted to derive the onset of the condensation-induced water hammer. The analytical model suggested that the map of the onset of the condensation-induced water hammer could be displayed by two essential non-dimensional parameters, such as modified Jakob number and Froude number. The model indicated that the slope of the boundary of the onset of the condensation-induced water hammer was the product of modified Stanton number, non-dimensional interfacial area concentration, and non-dimensional temperature difference. The model could predict the boundaries between no condensation-induced water hammer and non-periodic condensation-induced water hammer and between non-periodic condensation-induced water hammer and periodic condensation-induced water hammer satisfactorily. The one-dimensional nuclear thermal-hydraulic system analysis code, RELAP5, was used for simulating the onset of the condensation-induced water hammer. The obtained boundary corresponded to the experimentally obtained boundary between non-periodic condensation-induced water hammer and periodic condensation-induced water hammer.