Upgrading

Adding another layer of glass more than doubles the R-value of the window, but that’s still not great. You can have your windows triple-glazed, but this is extremely expensive and rarely cost-effective. Another way to add another layer of glazing other than buying double or triple pane windows is by installing storm windows or sheets of plastic over them. Windows allow so much more heat to escape than a well insulated wall that surrounds them. If you have many windows, your best option may be to insulate them rather than replace them.