The important task of the energy sector is to look for the ways of increasing energy efficiency of energy installations. This can be achieved by reducing heat losses. The thermovision technique is a very useful tool in this area. Owing to thermovision inspections it is possible to find the places with excessive heat losses as well as to determine them quantitatively. During the thermovision measurements it is necessary to know the temperature of the surroundings of considered object. A considerable group of energy installations are the objects placed in open air space. In such a case the surroundings constitute the ground and sky which are usually of different temperatures. During infrared inspections only one ambient temperature has to be entered into the camera system. The aim of this work was to develop a method for determination of equivalent ambient temperature representing thermally the surroundings of the object exposed to open air space. The use of long-wave infrared camera for sky temperature measurement has been proposed to carry out this task. Additionally, it has been proposed to use the aforementioned measurement results for the determination of total sky radiation temperature which is useful for radiative heat losses calculation. (C) 2015 Elsevier Ltd. All rights reserved.