If you think the multiple windows in your house need to be replaced - changing their size, moving them or just revising their design - keep in mind that you'll change the whole look of the house. So choose carefully and don't scrimp. This is a serious architectural decision in Belvedere Tiburon, California.

Besides appearance, other good reasons for spending on replacement windows are energy efficiency and ease of maintenance. The array of window replacement options today makes those important goals relatively easy to achieve. But it's still a complicated job. Poor installation can negate any advantages multiple windows will offer.

New windows won't solve structural problems unless the problem is in the window itself. But if openings are precisely measured, and windows are properly constructed and installed with care, a replacement project can reduce heat and air conditioning loss by up to 50 percent for a typical house.

If you live where it's cold in the winter and hot in the summer, new windows will pay for themselves in five to 10 years. You can roughly calculate the payback by multiplying your heating and air conditioning costs per year by 17.5 percent.