A high-precision high-voltage resistor must be cooled to ensure an adequate operation. The resistor consists of an arrangement of 3x10 resistances that dissipates 4W, disposed in a flat plate collocated at the center of a metallic electric shield. The resistor-shield system is placed in a metallic cylinder containing a fan at one end, to force air flow through the uniformlyperforated shield, in order to refrigerate the resistances. With this system, temperatures reached at the resistances were above the requirements. The aim of this work is to improve the ventilation system, in order to obtain the required values of temperature at the resistances, to ensure that its resistance remains virtually unaltered. Due to electric field restrictions, only the modification of the number (not increasing) and location of the holes was considered. Numerical 3D simulations using CFD&HT techniques were performed to test possible holes configurations. Moreover, experiments were performed for some hole configurations with the purpose of measuring the air flux and validating the model. The best configuration consisted of fewer holes than in the original design, placed in such a way that the flow at the interior of the capsule impacts directly on the resistances. Although the reduction of the number of holes causes a reduction in the total air flow, simulations show that the air velocity near the resistances is higher, resulting in higher cooling and temperatures being in an acceptable range.