In traditional buildings many climatic strategies have been used to provide indoor thermal comfort in south and central parts of Iran. A common element is called an iwan. This study investigates the indoor thermal comfort of a room adjoined to a talar in a traditional house which has an iwan, in Shiraz, Iran. The data related to the temperature and relative humidity of the room are used to calculate the thermal comfort index of PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) by considering the following two cases: a talar room with an iwan and one without an iwan, by means of DesignBuilder software. For the purpose of validation, the air temperature and relative humidity of the talar room with an iwan were measured over 10 days and compared to the results of the simulation. Having a valid simulation, computation was conducted for the selected house in various cases for an annual passive operation of calculating PMV and PPD. The numerical results revealed that the talar room adjoined to an iwan located in the south front of the courtyard had relatively good conditions during the hot months, including June and July. In addition, it could provide fully satisfactory comfort conditions during August and September. According to the results, it is found that the iwan makes a talar room 62% more desirable for the hot months in comparison with a talar room without an iwan.