The influence of different main design parameters on the heating/cooling potential of a sunspace connected with a building has been investigated in the present paper. The sunspace consists of a glazed enclosure, usually on the south side of a building and it is regarded as one of the most popular solar systems because of its potential as an energy collecting system and also because of its pleasant appearance. The dynamic thermal performance of the system for the winter and summer periods of the year and its operational limits have been calculated using an accurate transient thermal model environment. The simulated results showed that sunspaces can be an appropriate and effective system during the cold period of the year. However, they are, very often, responsible for overheating during the warm period of the year. An extensive sensitivity investigation is performed in order to analyse the impact of various main system's parameters, such as orientation, boundary conditions, glazing material, etc., on the energy potential of the system.