With growing population and rapid urbanization, energy demand for heating and cooling systems has increased substantially, driven primarily by the need to maintain thermal comfort for building occupants. Among building envelope components, transparent facades are major contributors to thermal energy loss: windows increase cooling loads in summer by allowing unwanted solar heat gain, and raise heating loads in winter through conductive heat transfer. Since cooling energy consumption typically exceeds heating demand, relying solely on energy intensity metrics is insufficient; thermal comfort needs must also be accounted for. This challenge is particularly significant in cities like Kashan, where both cooling and heating are required throughout the year. This study evaluates glazing optical properties and window-to-wall ratio (WWR) across different façade orientations of a residential apartment in Kashan, using the Predicted Percentage of Dissatisfied (PPD) index and Energy Use Intensity (EUI) as performance indicators. Results show that the optimal WWR is 30% for all three façades (south, north, and east), but the optimal glazing type differs by orientation. Low-E double-glazing was selected for the south and north façades, while tinted glazing was selected for the east façade. Following optimization, EUI decreased from 182.51 kWh/m² (energy grade C) to 159.66 kWh/m² (energy grade B), and PPD improved from 38.32% to 37.65%, with the south façade contributing most to this reduction. These findings demonstrate that analysing each façade's behaviour through the PPD index enables more accurate identification of occupants' thermal needs and supports the development of more effective thermal comfort strategies.