We just had new storm windows installed behind the stained glass windows on the staircase landing. They make a huge difference in preventing heat loss, and don't impact the way the glass looks from the inside (before this was done, we were getting frost on the interior of the stained glass!) Fortunately, almost all of the original windows in the house were replaced with new double-glazed windows before we bought it, and the few windows that haven't been replaced have decent storm windows. Our contractors also found that the entire house has blown-in insulation already -- excellent! The heating bill is still substantial, but (amazingly) it's no more than we were paying in our old apartment on Prospect Street, which was a much smaller flat on the second floor of a three-family house. There is definitely more we can do to tighten it up; we'll start with a (free!) Bay State Gas energy audit next month.