I get this question a lot from homeowners wanting to reign in their energy costs. Windows usually account for about a quarter of the heat loss in a typical house. State-of-the-art, triple-glazed windows (with two low-e coatings and krypton gas fill) will dramatically reduce that heat loss, so it would seem that replacing your windows would be one of the most sensible things we could do in buttoning up our homes—right?

Actually, the economics of window replacement are a good deal more complicated. Windows aren’t cheap—as anyone who has priced them recently knows. Top-performing windows with fiberglass frames and triple glazing are significantly more expensive than standard windows. Replacing all the windows in a typical house with such products is likely to cost well over $10,000, and the “payback” for that investment may be longer than the length of time you expect to be in your home.

What to do? I would start by getting an energy audit. A professional will examine your windows and should be able to give you a good idea of whether they need replacement. He or she may also be able to estimate what the energy savings would be from window replacement. (Note, however, that most energy auditors aren’t in the window replacement business, and they sometimes underestimate the benefits of window replacement.)

If your existing windows are in bad shape and need replacement, by all means upgrade with top-efficiency models—borrowing, if necessary, the extra money required to achieve this level of performance. The incremental cost of the high-performance windows (compared with standard windows) will be paid back through energy savings relatively quickly. But if your existing windows are in good shape, take a look at some other options before moving ahead with replacement—your energy auditor may be able to help you evaluate these options.

If your windows are a fairly standard size, it may make sense to replace just the sash rather than the whole windows. Sash replacement is a lot quicker and less expensive than whole-window replacement. If you replace older double-hung sash with new, your contractor may be able to remove the sash weights and insulate those sash-weight pockets (insulate with low-expanding foam sealant).

If your existing single-glazed windows are in reasonable condition and replacing the sash isn’t an option, installing storm windows often makes sense—this isn’t an option with casement or awning windows. Adding storm windows may even make sense if you have insulated glass in your prime windows, though the economic payback won’t be as fast.

I recommend outside-mounted, high-quality, triple-track, aluminum-framed storm windows. Quality is important, as they get a lot of wear-and-tear; triple-track means that there is an integral screen. Look for storm windows with low-e glass to boost performance. Harvey Industries, based in Waltham, Massachusetts, custom-manufactures such storm windows, though they have to be ordered through a builder or remodeler.

Since the low-e coating on a single-pane storm window will be exposed to air, it has to be a “hard-coat” low-e, which is more durable than the more common soft-coat low-e coatings. I have long looked for a quality insulated-glass storm window—so that you would end up with triple-glazed performance—but I’m not aware of any such product.

If your budget is too tight for new, high-quality storm windows, you might want to consider a less expensive, plastic, interior storm panel. If relatively handy with tools, you can make these yourself using materials available from Brown & Roberts or one of the local home centers. You can also order prefabricated, interior storm panels, such as those made by AEP Window Solutions, just across the Vermont border in Hoosick Falls, New York (518-686-9581). AEP custom-makes lightweight, removal, insulated panels (two layers of plastic) to fit your window frames at a significantly lower cost than replacement windows. The most budget-conscious homeowners or renters can simply tape or staple plastic on the inside of the windows—as I used to do—but this isn’t a permanent fix and it’s ugly.

Finally, you might want to consider repairing and air-tightening your existing windows—this can be done whether or not adding storm windows. Tom McLoughlin has recently moved to Brattleboro and set up a business specializing in window restoration. Thomas McLoughlin LLC Window Restoration (254-9370) preserves existing double-hung wooden windows, maintaining the historic character, while making them functional again and adding all-important weatherstripping.