In countries with extreme hot weather, the majority of the heat gain in residential buildings comes through thewindows. Exterior shutters are extensively founded in residential buildings in these countries to reduce the heat gain.Typically, the shutters are completely closed during the daytime, and such a condition creates a strong natural convectionflow in the space between shutter and window, which reduces the thermal effectiveness of the shutter. In this research, thethermal characteristics of a completely closed shutter are evaluated numerically and validated with experimentalmeasurement. A parametric study is conducted to assess the effect of natural convection flow in the space between theshutter and window, for month of May. The numerical results indicate that heat flux at the indoor surface of the glass isnearly independent of the thickness of the air space due strong natural convection flow in the space between the shutter andwindow.