Your house is the biggest waster of energy on the planet. A lot of that energy is in the form of heat, which, literally goes right out the window. There are products out there to help keep all that heat from leaving. Double pane windows are good, and now come standard with houses. Triple pane is even better. Then there are the gases that they stick inside the window to keep the heat in. Let's say you have one of these super windows, a triple pane, low e window, and let's even stick a film on it to help keep the heat in. Great isn't it? You pay all this money and expect it to work well. You have even had your old drafty windows replaced. Because you spent so much on it you want to save money on labor. They put it and it looks great! The heat is all being kept in, right?
Well, the problem was most likely not in the window and how many great things it had in it, but how it was installed. Single pane windows, yes, that is one sheet of glass, not even with a little air gap to help insulate, if properly installed is better than your super window poorly installed. You see, the energy that goes out the window is not the window itself, but those little gaps around the window. Those little gaps are not all bad either. In Germany they have well placed gaps to allow air movement to help with the house and how it is heated and cooled.
So, before you go and spend money to get that super window you think will help, maybe look at the good ones you have now and fix up those happy little gaps. And if you are building new, insist that the windows are installed properly, builders like to get away with things if it means less work for them.