answer:Depends on what you’re going from and to. If you have a single pane glass window and are upgrading with double pane insulated with a gas like argon, you’re going to be saving money on heating your home in the winter, as well as keeping it cool in the summer. That being said, remember windows aren’t the only ‘leaks’ of heat in your house. Check your door seals and skylights and any other structural elements that may cause a draft, because you may just end up negating the benefits of your expensive window replacement by not ensuring your entire home is tight. You may want to check around in your area to see if anyone has some form of thermoscope that’ll allow you to see the cold spots, since they may occur behind walls and such as well!