When you think about sealing a house, remember how much frigid air can go through a small opening in a sweater or a jacket. Even a tiny hole in a woolen mitten can make your finger numb with cold. The same thing can happen in a house. We had single-glazed, double-hung windows in that old prairie home where I grew up. In the spring, the windows were nice—we could open them wide to let in fresh breezes and the songs of meadowlarks announcing warmer weather. In the winter, though, that loose-fitting sash was a fright. My mother gave us thin strips of cloth to stuff between the window frame and