The system and method spatially predict the condensation of water and acid from the flue gas in the condensing heat exchanger installed in fossil power plant flue gas treatment system or similar environment. By modifying the operational conditions, the heat exchanger can control rates and areas of condensations. The system and method adjust either the cooling water temperature or the flowrate ratio of flue gas to cooling water to control the condensation rates of water or acids. The system and method also estimate actual coverage areas to apply for anti-corrosive coating onto the tube or duct surfaces to resist corrosion due to acid condensation. The system and method also optimize or customize condensation rates of water and acids in boiler flue gas under operating conditions given at a power plant.