Condensation on the inside of your windows is simply a product of the humidity IN your home and the temperature of the class on which the humidity (water vapor) is condensing. It is a normal natural phenomenon as long as it is occurring on the surface of the glass where you can wipe it off. It is NOT a normal occurrence if it is happening between the vacuum sealed panes and you cannot get to it to wipe it off. This indicates that the vacuum seal has been ruined, either in manufacture or during installation. It is VERY common for carpenters to bind, bend or otherwise destroy this vacuum seal and manufacturer's reps are good at detecting this problem.