A linearized formulation of the basic fluid conservation equations for describing the dynamic behavior of nuclear steam generators is presented. The model utilizes a movable boundary spatial discretization technique in one-dimensional geometry and is capable of representing the transient behavior of integral-economizer once-through steam generator (IEOTSG) units in the time and frequency domains. A generalized boundary treatment algorithm is developed to place and track boundaries between heat transfer regimes on the secondary side of a steam generator. An enthalpy transport model is incorporated in a manner consistent with the movable boundary formulation to reduce the nonphysical representation of the in-cell distribution of enthalpy with long axial regions and weighting functions. Results of transient calculations performed with the linearized model agree well with other computational results, as well as with the experimental data obtained at a 19-tube IEOTSG test facility.