The cost of electricity incurred for providing a thermally comfortable living space in big cities like Jakarta, by using fans and air conditioners, takes up to 32,41% of the overall utility cost per low-income household. The use of air conditioners by the low-income residents of a number of rusunawas in Jakarta, however, is clearly observable from the outside. This condition not only emphasizes the importance of a thermally comfortable living space but also the impact of the architects’ decisions in designing affordable vertical housings on the economy of the occupants. The aim of this study is to find the impact of the architect’s design decisions as reflected in the building shape and orientation as well as the opening dimensions on the thermal comfort as experienced by the residents and how it further affects their economy. This study uses rusunawa Pengadegan in South Jakarta as its research location. The study was conducted by developing a thermal comfort simulation and an observation on the evidence of use of air conditioners followed with a predictive calculation on the affected electricity cost. The aim is to examine the suitability of the rusunawa design toward the economic livelihood of the residents in the long run.