A Computer Aided Engineering (CAE) model has been developed to predict vehicle heater system warm-up performance for quasi-transient (standard wind tunnel warm-up) and fully transient (city traffic) test conditions. The transient responses of the heater system in terms of three metrics, coolant temperature at the heater inlet, discharge air temperature, and average vehicle interior temperature, are calculated. Predicted results are validated by comparing to experimental test data. The base CAE model can be expanded to evaluate any duty cycle.This analytical tool can be used to provide component selection information during the early design stages before conducting physical tests or to evaluate the performance impact of a design change (“A” to “B” comparison). This can reduce development time and cost by reducing the required number of prototypes and physical tests.