In this paper a new methodology for the comprehensive evaluation of the thermal condition of environment based on operative temperature thermal levels, so called decitherms, is presented. It allows an assessment based on the perception of the environment by man. It stems from the impact of the environment on human psyche as described by the Weber-Fechner law. One of its strengths is that it takes into account the fact that a decrease in operative temperature is perceived the more strongly at lower temperatures. The concept of the decitherm allows a direct numerical comparison with decibels, used for noise evaluation, and with deciodors, used for odor assessment, and additionally the total environment can be assessed by adding the individual levels multiplied by corresponding impact factors. Further, concrete values for SBS can be estimated, rating of air-conditioning systems efficiency defined and the degree of danger to man whether by overheating (hyperthermia) or undercooling (hypothermia) can be estimated. This methodology has already been used in the preparation of European standard prEN 4666:2011 Aerospace Series, Aircraft integrated air quality and pressure standards, criteria and determination methods. (C) 2014 Published by Elsevier B.V.