I couldn't help but respond. Please check with a home improvement expert or your local utility company for precise information. But I will tell you this. There are many different types and models of double pane windows. Some are merely vacuum sealed and less expensive the most expensive "e-glass" windows are filled with Argon gas to be more energy efficient. There maybe some filled with nitrogen but that would be new to me. You absolutely can have one pane replaced at a specialized shop because I have done so a a much reduced price. You must take the window to them but mine were the tint in type douple hung and was easy to remove and take to the shop. Everyone on the internet is an "expert" with all the answers but many are ill informed or just plane wrong. Again please go to your local electric utility and get the correct information. This I promise, double pane of any variety is much more efficient than single pane and your energy bills will be significantly reduced by having them.
