By Steve Jordan (hyperlinked from oldhousejournal.com)

Does the return of cold weather tempt you to consider high-powered ads for new windows that promise to lower your energy bills and add value to your home—all for "one-time-special" offers? Well, think again. Your old, sticky, low-tech windows are probably more cost-effective than they seem. They simply need a little tender loving care to provide efficient, trouble-free service for another half century or so. Cleaning off old paint drips and tightening up the stops works miracles, but adding efficient, top-of-the-line weather strips can make your windows competitive with the best of replacement systems.
 

Look for Problems
First, take time to assess the working condition of your windows. Before examining the window itself, look for drafts with the time-honored smoke test—that is, on a windy day, pass a smoke source (a cigarette, incense stick, or candle) around the frame and see if you can pinpoint any conspicuous air leaks...more

Adjust Sash Stops
Sash stops—the two vertical mouldings just inside the window—serve two functions: They hold the sash in place, but they also adjust to secure the sash against wind infiltration. When sash stops are attached with nails, they cannot be adjusted, so their initial placement must be a careful balance—not too tight and not too loose...more

Weather strip Lower Sash
When upgrading historic windows in cold climates, combining weather strips with the above mentioned tune-ups creates the most energy efficient installation. Although there are many methods and materials used to weather strip windows, I generally choose durable metal weather strips. When pliable weather strips are called for, I use only EPDM rubber because it lasts longer than inexpensive vinyl alternatives and is not vulnerable to temperature changes...more
 

Install Storm Windows
Energy studies conducted by the federal government and many universities indicate that the combination of an adjusted prime sash and good storm sash is as efficient as most replacement windows. The best storms—thermally and aesthetically —are wood-framed but, alas, these have worn out their welcome with all but a few die-hard preservationists...more