You'll pay: Aluminum double-track interior storm windows start about $40 each; basic doors are a few hundred. Qualified exterior storm windows, often used for historic windows, are about $100 each.
You'll save: As much as 15 to 20 percent on heating and cooling, especially in cold climates.
Why do it now? For historic homes, where replacement windows or new doors might give an owner pause, storms go a long way toward improving efficiency and comfort. Exterior storm windows can also help seal out moisture and protect wooden sash.
What to look for: Requirements for qualifying products vary for different windows and regions. Many storms are now made with low-E coatings, like exterior windows, and double-track windows are available with enamel coatings, which are easier to slide up and down than aluminum ones.
Bottom line: If you lack the bucks for new windows or want to preserve the originals, storms are an excellent intermediate measure.