A method and system for predicting heat exchanger blockage in an aircraft is provided. The method includes generating a reduced order model (ROM) that predicts a ram air fan (RAF) surge margin that correlates to a heat exchanger blockage parameter, calculating, using the ROM, a predicted RAF surge margin value using a sensor signal received from a sensor connected to a ram air fan (RAF), calculating the heat exchanger blockage parameter using at least the predicted RAF surge margin value, and reporting, to a user, the heat exchanger blockage parameter that indicates when a heat exchanger blockage condition is present.