Recessed spaces outside high-rise residential buildings of public-type in Hong Kong often contain a large number of condenser units of window-type air-conditioners that during summer reject heat into this space at the same time. For four condenser units per story, a computational fluid dynamics (CFD) code is used to predict temperature and flow fields inside the recessed spaces that differ in heights and condenser-unit locations. The results show that a powerful rising hot air stream and one vortex pair are formed in the space near to its corner wall. In addition, the results show that condenser units will suffer more when they are placed inside the taller recessed space, and at locations higher at this space and nearer to its corner wall. Then, these units would draw less air at an elevated temperature, and therefore become less energy efficient and de-rated in output capacity and sometime have interrupted operation. However, the condenser units at lower levels may benefit because they will draw more air at nearly environmental temperature.