In order to evaluate comfort conditions inside a room it is necessary to estimate the mean radiant temperature (Tmrt) distribution on it. The generally accepted method to calculate radiation exchange within non-participating enclosures is the Radiosity Intensity Method (RIM). However it is very difficult to compute mean radiant temperatures with this method. This paper proposes the use of a new version of the Discrete Transfer Method (DTM). The DTM has been used before inside combustion chambers and furnaces but rarely in non-participating enclosures, such as a room. However, the Discrete Transfer Method can be used in these kind of enclosures, as this paper demonstrates, to compute the mean radiant temperature. The types of building enclosures examined are ones with with radiant heating panels, windows, and direct solar gain.