In my diploma thesis I analysed indoor work environment in generic business premises, within which I focused both on visual as well as thermal comfort. Using the software tool Comfen, I researched how size, type of window and non-use of shadows or light shelfs affect results. I analysed 5 different sizes and 4 different types of windows. The purpose of this thesis was to find a connection between visual and thermal comfort, which would provide us with the optimal comparisson for both parameters. I defined values of useful daylight illuminance, known as well as UDI, by using calculation of hourly illuminance on average day of specific season. Simulation of illuminance was made in two reference points. Comfen gives us results for thermal comfort as calculations of predicted percentage of dissatisfied users, PPD, throughout the average day of specific season. I collected the results as points in coordinate system, where x-axis is represented as thermal comfort and y-axis as visual comfort. Due to the fact that I analysed 20 different scenarios in 2 different reference points for 4 seasons, my coordination had in total 160 points. In order to make the result more legible I combined the results as points for a whole year and business premises as one entity. In my research I used geometric mean as a tool to combine values of both visual and thermal comfort into one representative value. That way I got for my final comparison only 20 results. At the end I defined the optimal scenario, showing us which size and type of window give us the best results taking into consideration both . I comment on the results based on my input data, presumptions and restrictions and add a perspective on possible further analysis and research of this problem.