This paper proposes a verification and calibration method for thermal imagers that consists in comparing temperature readings obtained by contact- and thermal imaging methods. In order to confirm the reliability of the proposed method, an experimental setup was developed, whose main element comprises an emitting surface in the form of a 330 × 200 × 4 mm rectangular plate covered with paint having an emissivity factor not less than 0.96. The paper presents the results of temperature field calculations on the plate’s emitting surface. The temperature field of the plate’s emitting surface was determined by the contact method using chromel-alumel thermocouples, as well as the thermal imaging method. As a result of the obtained temperature values analysis, it is concluded that the heat exchange of the plate with the ambient air starts to play a significant role when the temperature of the emitting surface approaches 50°C. Therefore, air heaters were applied in order to reduce the dissipation of heat from the emitting surface into the environment. These heaters are two aluminum-magnesium alloy plates attached to the end face of the emitting surface. The metal heat exchanger coils are installed on the surfaces of the plates and connected by hoses to the liquid thermostat. One of the plates heats the air flowing around the emitting surface, while the other prevents the thermal emission into the environment. As a result of the application of the heaters, the heat exchange intensity of the radiating surface of the plate with the environment decreases. Recommendations about the choice of heater sizes are given. The main advantages of the proposed method are the following: ensuring high isothermicity of the emitting surface throughout the thickness of the plate; accuracy of the temperature maintaining at a given level; reducing the transition time of the device to a steady-state regime.