Boost your home's value

Payback: 77% to 79%

Cost: $11,000 to $18,000 to replace 10 standard-size windows

When it makes sense: Your windows are starting to rot or degrade, or they're letting too much hot or cold air escape.

Best way to do it: Look for windows certified by both the American Architectural Manufacturers Association (AAMA) and the National Fenestration Rating Council (NFRC). The windows should have a good rating for energy efficiency and a Low-E coating, which bounces back the sun's heat. You'll immediately start reaping the benefits: Energy-saving windows can chop your heating and cooling costs by 30%.

Caveat: Even if you spring for a fancy wood window, if it doesn't match the age or detail of your house, "it's going to make the house look cheap," says Tom Silva, a general contractor and expert on the PBS show This Old House.

Cost-saving move: Buy wooden windows that have vinyl wrapped on the outside. You'll save on maintenance later.

NEXT: Go a little (or a lot) greener