One of the fundamental human requirements is a working environment that allows people to perform their work optimally under comfortable conditions. Given that buildings and air conditioning systems are designed on the basis of a certain level of discomfort, this raises the key question ‘What is the effect of the level of comfort on the productivity of people working in office environments?’ The purpose of this paper is to quantify this relationship as an aid to making choices regarding the working environment at strategic level within the facilities management process, with particular emphasis on thermal conditions.