If you want to upgrade your old windows, be sure to check out the benefits of triple-pane windows as well as double-pane. In cold regions, such as New England, triple-glazed windows can save 2 to 3 percent of your heating bill, compared with double-glazed windows. From a cost standpoint, it'll take a few decades to recoup the 10 to 15 percent upcharge to go from low-e double-glazed windows to triple-glazed. For example, if you pay $1,000 per year in energy bills, have 20 windows in your house, and 22 percent of your energy is lost through your windows (which is average), then each window is losing $11 worth of energy per year. A triple-glazed window will reduce that loss by about $1, so it'll take 35 years to cover a $35 upcharge for triple-glazing. Of course, if your energy bills and energy loss are greater, you'll recoup the cost sooner.
However, the investment may be worth the cost in terms of comfort. Triple glazing will reduce condensation, which will allow you to maintain a higher indoor relative humidity in cold weather. These windows also reduce cold drafts. If you don't want to pay for triple-pane windows throughout the house, get them for the north- and east-facing rooms, where you'll get the biggest payoff.
Most of the major window manufacturers in the United States don't offer triple glazing. But here are two that do: Marvin and Weather Shield. Many Canadian window manufacturers offer triple glazing.