5. Plant deciduous trees

Plant trees now on the south, east, and west sides of your house, and you can picnic under them in a couple of years. In five years, they may provide enough shade to let you run your air conditioner less frequently. And when the trees mature, they could save you as much as 40 percent on your cooling costs. Beyond shading your property, trees also help combat the "heat island" effect that occurs in urban areas, where concrete and asphalt absorb and hold in heat. Two popular varieties are red oak for large lots (it grows to 70 feet) and trident maple for small ones. But before you buy any saplings, check with your city's public works department; some trees have invasive roots that plug water or sewer lines.

*Total: $35-$50 per tree

6. Install a programmable thermostat

With an estimated annual savings of $100 and an initial outlay of only about $50, few upgrades pay for themselves as quickly as this one can. With a programmable thermostat, you can automatically adjust your heating and air-conditioning systems to match your family's seven-day-a-week schedule. During the winter, for example, you can set it to turn off the heat after everyone's snug in bed, switch it back on in time for a warm wake-up, then putter along at a lower temp until the kids get home from school. The most advanced models let you program up to four settings for each day of the week. For every degree you lower your thermostat for an 8-hour period, you cut energy use by about 1 percent. Set it back 10 degrees overnight, and that's a 10 percent savings right there. And we bet you won't even feel the difference—except when you're paying the bills.

*Honeywell T8112 Seven-day Thermostat: $49

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