This paper describes an advanced monitoring system for fouling phenomenon in a wide range of tubular heat exchangers such as condensers and intercoolers. First, a mathematical model of fouling resistance in tubular heat exchangers is adapted. The model is based on the applied thermal power, the inside heat transfer coefficient, and geometrical characteristics of the heat exchanger under consideration. The resulting model is a function of measured quantities such as water and tube wall temperatures, fluid flow velocity, and some physical properties of the fluid flowing inside the tubes, such as viscosity, conductivity, and density. Second, an on-line fouling monitoring system was prepared, and the heat transfer resistance for selected solutions was measured in real time by this system. The effect of concentration and chemical reactions on fouling was studied experimentally using contaminants such as sodium bicarbonate, sodium chloride, calcium chloride, and a mixture of sodium bicarbonate and calcium chloride. Experimental results provide quantitative information of liquid-side fouling on heat transfer surfaces, and its effects on the thermal efficiency. Experimental data are critical for heat exchanger design and for planning operating and cleaning schedules of the heat exchanger. Uncertainty analysis shows that the experimental results are acceptable and the experimental setup is appropriate for measuring fouling resistance in industrial applications.