A parametric study is carried out numerically to investigate fluid flow and heat transfer characteristics in double, triple and quadruple pane windows considering various gap widths together with different emissivity coatings. A comprehensive numerical study has been conducted to investigate fluid movements and conjugate heat transfer of natural convection, conduction and radiation in the multiple pane window arrangements. Computations are performed for both air-filled and argon-filled windows. Indoor and outdoor temperatures are kept constant and convective boundary conditions are applied on the inner and outer pane surfaces of the window units to reflect realistic conditions. Computations show that the most reasonable gap width is 12 mm for all cases considered in this study. The effect of gas filling on the U-value is more pronounced for the windows coated with low emissivity materials. Installing quadruple pane windows having low emissivity coatings and low conductance gas filling, the U-value can be decreased to the level of 0.4 W/m(2) K. The main contribution of this study is to present correlations for predicting the glazing U-value considering the number of the panes, emissivity of the glass surfaces and gap width of the cavities for air-filled and argon-filled multiple pane windows. (C) 2014 Elsevier Ltd. All rights reserved.